For homeowners, buyers, building owners, and anyone reading a roofing proposal

Roofing glossary

Reference · steep-slope and low-slope · United States

The definitions the rest of this site links to. Grouped by the part of the roof each word belongs to, because that is how the words are actually used — and because a reader who does not know a term rarely knows its first letter matters.

30-second answer

What does this roofing word actually mean?

Roofing vocabulary is inconsistent: the same word can mean one thing in a contract, another in a code, and a third on a job site. This page defines 241 terms, groups them by the part of the roof they belong to, and gives each a permanent link any page can point at. Where a word is genuinely ambiguous, it says so.

Stop — immediate hazard

If you are looking up a word because something is wrong right now

A sagging or dipping roof or ceiling, water running near lights, outlets, or a panel, a burning smell, a downed line touching the house, or active flooding are not roofing questions. Get people out and keep everyone clear of the ground below the affected area.

Nothing on this page needs you on a roof or in an attic. OSHA requires trained workers in residential construction to be protected against falls at six feet, and reports that falls are the leading cause of death in that work. Assessment from the ground, from a window, from photographs, or from a professional is the path this site will always point at.

Leave the area and call your utility, the fire department, or 911 first. A definition can wait; none of the situations above can.

Learning paths and saved lessons

How to use this page

A reference, not a reading assignmentSection link

Search the page for the word you have, or jump to the group it belongs to. Every term has its own permanent link, so a definition can be sent, bookmarked, or cited on its own.

Terms defined: 241Counted from the page itself rather than claimed.
Groups: 12, by part of the roofStructure through code, following how a roof is built and then bought.
Anchors: One per termFor example /roofing-glossary/#drip-edge. Ids are stable even if the wording changes.
What this page is not: Not code, not a quote, not a diagnosisDefinitions describe words. What is required at a property is set by the jurisdiction; what a project costs is set by a signed scope of work.

Tradeoffs

What a definition can and cannot settleSection link

Vocabulary is a tool with a specific reach. Here is where it helps and where using it as evidence goes wrong.

Best when

You are reading a proposal, an inspection report, or an insurance scope and want to know what a line item is.
You are comparing two quotes and need to check that both are describing the same work in the same units.
You want to ask a contractor a precise question instead of a general one.
You are writing or reviewing a scope and want the specific word rather than the approximate one.

Think twice if

You are trying to establish what is required at your property — that is set by the adopted code edition and the authority having jurisdiction, not by a definition.
You are interpreting a warranty or an insurance policy: only that document, read in full, says what it covers.
You are deciding whether damage is functional or cosmetic. That is an inspection finding about a specific roof, and no glossary can make it remotely.
You are about to act on a definition by getting onto the roof yourself. Nothing here is worth that.

What changes the answer

Jurisdiction and adopted code edition, which change what a term such as ice barrier or recover actually requires.
The manufacturer’s published instructions, which govern exposure, nailing zone, slope limits, and what voids a warranty for that specific product.
Region and trade custom — some of these words carry local meanings that are perfectly clear to everyone on one job site and wrong two states away.
The contract in front of you, which can define a term differently from the whole industry and still bind both parties.

Orientation

The words follow the layersSection link

Almost every roofing term names a layer, a junction between layers, a unit of measurement, or a way one of those fails. Learning them in that order is faster than learning them alphabetically.

Jump to a group:

Structure and framing
Shape, planes, and geometry
Layers of a steep-slope assembly
Steep-slope coverings
Low-slope and commercial systems
Flashing, edges, and details
Ventilation, air, and moisture
Measurement, quantities, and units
Fasteners and attachment
Damage, wear, and failure modes
Contract, quote, and insurance vocabulary
Code, testing, and listing terms
The words that carry two meanings — a comparison table
One roof, taken through every unit — a worked example

Section through a steep-slope roof at the eave, drawn to show the order of the layers rather than their real thickness. The numbers are keyed to the glossary entries listed underneath.Original diagram, Understanding Roofing. Layer order follows U.S. Department of Energy Building America Solution Center guidance for asphalt shingle roofs and vented attic construction. Not to scale; not a construction detail.

Key to the diagram: 1. Roof covering·2. Ice barrier·3. Underlayment·4. Roof deck·5. Rafter·6. Drip edge·7. Fascia and gutter·8. Soffit vent (intake)·9. Ventilation baffle·10. Air barrier and ceiling insulation·11. Attic space·12. Ridge vent (exhaust)

Why the grouping is by part, not by letter

An alphabetical list works for someone who already has the word. Most people arrive here with a thing rather than a name — a strip of metal at the edge of the roof, a black band showing under the first course, a line item they did not expect on a quote. Grouping by the part of the roof a word belongs to lets you find a term you cannot yet spell, and it puts the terms you are likely to need together next to each other. Your browser’s find-on-page still works if you do have the word: everything here is static text, in one page, with no tabs or accordions hiding it.

Where the trade genuinely disagrees, this page says so

Roofing vocabulary grew out of several traditions — carpentry, sheet metal, bituminous waterproofing, insurance adjusting, and building science — and they did not standardise before they had to share a job site. Pitch means one thing to a framer and another in a nineteenth-century pattern book. Shake means something to a modern supplier that it did not mean when the roofs those products imitate were built. Where a term is contested, the entry says which usages exist and gives you the question that resolves it, rather than picking a winner and leaving you to be misunderstood.

The three ideas that make the rest of it make sense

First, a roof is an assembly, not a covering: the deck, underlayment, control layers, fastening, and flashings all participate in how it performs, which is why classifications belong to tested assemblies rather than to products. Second, the covering sheds most of the water and the details handle the hard part — the junctions at walls, chimneys, valleys, and edges are where roofs actually leak. Third, everything under the deck is a heat, air, and moisture problem, and a roof that fails from underneath fails in exactly the same way whether or not the shingles are new.

Original analysis

The words that carry two meaningsSection link

A glossary that pretends the trade agrees with itself is not much use. These are the terms where the job-site meaning and the code, standard, or contract meaning genuinely differ — and where that gap costs people money.

Twelve roofing terms with more than one working meaning, and the question that resolves each one. Compiled by Understanding Roofing from the sources listed at the foot of this page.
Term	How it is used on a job site	How it is used in a code, standard, or historic record	The question that settles it
Pitch / slope	Used interchangeably for rise per 12 inches of run.	Historically pitch meant rise over the full span, so “quarter pitch” is a 6:12 roof on a 24-foot span.	Ask for rise in inches per 12 inches of run. Every material limit and code threshold is written that way.
Shingle / shake	Shake means a thick, rough, split-look unit; shingle means a thinner sawn one.	The National Park Service records that historically all wooden roofing units were called shingles, split or sawn, and that “shake” is a recent commercial distinction.	On a proposal, a look is not a specification. Pin it to a product, thickness, and grade.
Square / square foot	A square is 100 square feet of roof surface.	Contracts and material lists mix both units, and insurance scopes work in squares.	A per-square price is 100× a per-square-foot price. Confirm which unit a number is in before comparing two quotes.
Recover / overlay / re-roof	All three get used for “new roof over the old one”.	Adopted codes treat recover as a defined operation with conditions attached, and re-roofing covers both recover and full replacement.	Ask explicitly: is the existing covering coming off? The answer changes price, deck inspection, weight, and what a code permits.
Underlayment / ice barrier	Both called “the paper” or “the felt”.	An ice barrier is a self-adhered membrane with a required extent where a jurisdiction requires it; underlayment is the sheet over the rest of the deck.	They are separate line items with separate products. A quote naming only one of them has priced only one of them.
Flashing / counterflashing	“Flashing” is used for the whole detail, and often for sealant.	Base flashing and counterflashing are two overlapping pieces with different jobs, installed at different times by different trades.	Ask which pieces are being replaced. Reusing counterflashing is sometimes correct; reusing rusted base flashing rarely is.
Deck / decking / sheathing	Three words for the same surface.	Specifications and codes prefer “roof deck”; lumber suppliers say sheathing.	No difference in meaning. There is a large difference between inspecting it and replacing it — that is the line item to read.
“Class 4” / impact resistant	Sold as hail-proof, and sometimes tied to an insurance discount.	A UL 2218 classification from a steel-ball test, judged on a breach seen from the back of the specimen.	It is a laboratory class, not a warranty against hail. IBHS evaluates deformation and granule loss too — the damage people actually see.
“Class A” / fire rated	Attributed to a shingle by itself.	A classification earned by a tested assembly under UL 790 / ASTM E108, in which the deck and underlayment participate.	Ask which assembly. Substituting a component can change the classification the roof actually has.
“1/300 ventilation”	Quoted as a universal rule.	A ratio that applies under conditions set by the adopted code edition — and 1/150 applies in other situations.	Correctly designed unvented assemblies are legitimate too. The ratio needs an assembly, a climate zone, and a jurisdiction before it means anything.
“30-year shingle”	Heard as a service life.	A warranty term describing a limited, usually prorated remedy — not a prediction of how long the roof lasts.	Service life is a planning range driven by ventilation, exposure, slope, colour, and installation quality. Ask for the warranty document.
Membrane / coating	Both described as “a flat roof”.	A membrane is the waterproofing system; a coating is a liquid-applied surface over something else.	A coating over wet insulation or failed seams postpones a replacement. A moisture survey and core cuts are how you tell.

Read this table one item at a time

Pitch / slope

How it is used on a job site: Used interchangeably for rise per 12 inches of run.
How it is used in a code, standard, or historic record: Historically pitch meant rise over the full span, so “quarter pitch” is a 6:12 roof on a 24-foot span.
The question that settles it: Ask for rise in inches per 12 inches of run. Every material limit and code threshold is written that way.

Shingle / shake

How it is used on a job site: Shake means a thick, rough, split-look unit; shingle means a thinner sawn one.
How it is used in a code, standard, or historic record: The National Park Service records that historically all wooden roofing units were called shingles, split or sawn, and that “shake” is a recent commercial distinction.
The question that settles it: On a proposal, a look is not a specification. Pin it to a product, thickness, and grade.

Square / square foot

How it is used on a job site: A square is 100 square feet of roof surface.
How it is used in a code, standard, or historic record: Contracts and material lists mix both units, and insurance scopes work in squares.
The question that settles it: A per-square price is 100× a per-square-foot price. Confirm which unit a number is in before comparing two quotes.

Recover / overlay / re-roof

How it is used on a job site: All three get used for “new roof over the old one”.
How it is used in a code, standard, or historic record: Adopted codes treat recover as a defined operation with conditions attached, and re-roofing covers both recover and full replacement.
The question that settles it: Ask explicitly: is the existing covering coming off? The answer changes price, deck inspection, weight, and what a code permits.

Underlayment / ice barrier

How it is used on a job site: Both called “the paper” or “the felt”.
How it is used in a code, standard, or historic record: An ice barrier is a self-adhered membrane with a required extent where a jurisdiction requires it; underlayment is the sheet over the rest of the deck.
The question that settles it: They are separate line items with separate products. A quote naming only one of them has priced only one of them.

Flashing / counterflashing

How it is used on a job site: “Flashing” is used for the whole detail, and often for sealant.
How it is used in a code, standard, or historic record: Base flashing and counterflashing are two overlapping pieces with different jobs, installed at different times by different trades.
The question that settles it: Ask which pieces are being replaced. Reusing counterflashing is sometimes correct; reusing rusted base flashing rarely is.

Deck / decking / sheathing

How it is used on a job site: Three words for the same surface.
How it is used in a code, standard, or historic record: Specifications and codes prefer “roof deck”; lumber suppliers say sheathing.
The question that settles it: No difference in meaning. There is a large difference between inspecting it and replacing it — that is the line item to read.

“Class 4” / impact resistant

How it is used on a job site: Sold as hail-proof, and sometimes tied to an insurance discount.
How it is used in a code, standard, or historic record: A UL 2218 classification from a steel-ball test, judged on a breach seen from the back of the specimen.
The question that settles it: It is a laboratory class, not a warranty against hail. IBHS evaluates deformation and granule loss too — the damage people actually see.

“Class A” / fire rated

How it is used on a job site: Attributed to a shingle by itself.
How it is used in a code, standard, or historic record: A classification earned by a tested assembly under UL 790 / ASTM E108, in which the deck and underlayment participate.
The question that settles it: Ask which assembly. Substituting a component can change the classification the roof actually has.

“1/300 ventilation”

How it is used on a job site: Quoted as a universal rule.
How it is used in a code, standard, or historic record: A ratio that applies under conditions set by the adopted code edition — and 1/150 applies in other situations.
The question that settles it: Correctly designed unvented assemblies are legitimate too. The ratio needs an assembly, a climate zone, and a jurisdiction before it means anything.

“30-year shingle”

How it is used on a job site: Heard as a service life.
How it is used in a code, standard, or historic record: A warranty term describing a limited, usually prorated remedy — not a prediction of how long the roof lasts.
The question that settles it: Service life is a planning range driven by ventilation, exposure, slope, colour, and installation quality. Ask for the warranty document.

Membrane / coating

How it is used on a job site: Both described as “a flat roof”.
How it is used in a code, standard, or historic record: A membrane is the waterproofing system; a coating is a liquid-applied surface over something else.
The question that settles it: A coating over wet insulation or failed seams postpones a replacement. A moisture survey and core cuts are how you tell.

This table is about vocabulary, not about compliance. Nothing in it determines what is required at a particular property — that is set by the code edition adopted there and confirmed by the authority having jurisdiction.

Group 1 of 12

Structure and framingSection link

What holds the roof up. These words decide whether a building can carry a heavier covering at all, and they are the ones a structural question gets answered in.

Rafter: A sloping framing member running from the wall plate up to the ridge. Rafters are cut and assembled on site, which is why an older rafter-framed attic is usually one open space, while a trussed one is filled with the webs of the trusses.
Truss: A factory-built triangulated frame that spans wall to wall in one piece. The webs are structural, so cutting or notching one to make room for storage, a duct, or a skylight is a structural alteration, not a carpentry detail. See also rafter.
Ridge board: A non-structural board the tops of opposing rafters land against. It aligns the rafters; it does not carry them. A ridge board is why opposing rafters must be tied at the bottom, or the walls spread.
Ridge beam: A structural beam that actually carries the upper ends of the rafters down to posts and a load path below. Cathedral ceilings and vaulted rooms usually depend on one. A ridge board and a ridge beam look similar from the attic and behave completely differently.
Collar tie: A horizontal member connecting opposing rafters in the upper third of the roof. It resists the rafters separating at the ridge under uplift; it is not what stops the walls from spreading.
Rafter tie: A horizontal member near the bottom of opposing rafters — often the ceiling joists themselves — that resists the outward thrust a sloped roof puts on the walls. Removing rafter ties to open up a ceiling is the change that most often causes walls to bow outward. Not the same thing as a collar tie.
Purlin: A member running horizontally across rafters or trusses. In light-frame houses purlins brace long rafters mid-span; in metal buildings, purlins are the framing the roof panels fasten to and there is no continuous deck.
Top plate: The horizontal lumber at the top of a wall that the rafters or trusses bear on. The joint between the top plate and the ceiling is one of the largest air-leakage paths in most houses, which is why it matters to roof performance, not just to framing.
Birdsmouth: The notch cut into a rafter where it sits on the top plate. Its depth is limited: over-cutting a birdsmouth removes bearing area from the rafter at the exact point where the load transfers.
Roof deck: The continuous surface fastened over the framing that everything else is attached to — usually plywood or OSB on houses built since the 1970s, board sheathing before that, and steel, concrete, or wood on commercial buildings. Also called sheathing or decking; the three words are used interchangeably in the trade. Deck condition is the single most common reason a roof price changes mid-project.
Skip sheathing: Spaced boards rather than a continuous deck, used under wood shakes and some tile so the underside can dry. Also called open lath or battens. A house with skip sheathing usually needs a new continuous deck before it can take asphalt shingles — a cost that does not appear in a per-square price. See roof deck.
Panel edge clip: A small H-shaped metal clip fitted between sheathing panels where the edge is unsupported by framing. Also called an H-clip. Its absence shows up years later as a wavy roof surface at the panel joints.
Span: The horizontal distance a framing member covers between supports. Allowable span depends on species, grade, depth, spacing, and the load being carried, which is why span is answered from a table or an engineer for the specific building rather than from a rule of thumb.
Dead load: The permanent weight of the building itself, including the roof assembly. Going from asphalt shingles to concrete tile or slate can multiply the roof’s dead load several times over, which is why a material change of that kind is a structural question first. See pounds per square.
Live load: Temporary load — workers, equipment, stacked materials. It is why a roof that carries its covering fine can still be overloaded during a re-roof when bundles are stacked in one place.
Snow load: The design load from accumulated snow, which varies by location, elevation, roof shape, exposure, and drift conditions, and is set by the code adopted where the building is. Sliding and drifting concentrate snow far above the flat-roof number. There is no national snow load; see authority having jurisdiction.
Deflection: Bending under load. Visible sag between rafters usually means sheathing deflection; a ridge or plane that dips in a long curve is a framing question. Either one seen for the first time after snow or water accumulation is a reason to leave the area and call a professional — see the safety note at the top of this page.

Group 2 of 12

Shape, planes, and geometrySection link

The words for where you are standing on a roof, and for how steep it is. Slope decides drainage, material eligibility, labour, and how much roof there is to buy.

Roof plane: One continuous flat surface of a roof. Quantities are measured plane by plane; a house described as “1,800 square feet” may have four planes, or fourteen, and the difference is most of the price difference between two similar-sized roofs.
Ridge: The horizontal line where two roof planes meet at the top. It is the highest point of the assembly and, in a vented attic, the usual place for exhaust air to leave.
Hip: The sloping external corner where two roof planes meet and shed water away from the line. Hips add cut waste and labour compared with a plain gable, and remove the flat end walls that gable roofs present to the wind.
Valley: The sloping internal corner where two planes meet and concentrate water into the line. Valleys carry more water than any other part of the field, which is why they are detailed differently — see open valley and closed valley.
Eave: The lower edge of a roof plane, including any overhang past the wall. The eave is where water leaves, where intake ventilation usually enters, and where ice dams form. See fascia, soffit, and ice dam.
Rake: The sloping edge of a roof plane at a gable end. Rake edges take direct wind and are a common starting point for blow-off when the covering is not properly secured or the edge metal is missing.
Gable: The triangular section of wall enclosed by two sloping roof planes, and by extension the roof shape that has one. Gable ends are the wall, not the roof — but they are the surface that fails in high wind on many older houses.
Hip roof: A roof that slopes on all sides with no gable ends. Hip geometry generally performs better under wind than a comparable gable, costs more to frame and cover, and leaves less continuous run for ridge ventilation. See roof types.
Gambrel: A two-slope-per-side shape — shallow above, steep below — most associated with barns. The break line between the slopes is a detail that has to be flashed, and the steep lower face behaves more like a wall than a roof.
Mansard: A four-sided version of the same idea, with a near-vertical lower slope on every side. Because the lower face is close to vertical, the material and fastening appropriate for it may differ from the flatter upper roof.
Shed roof: A single plane sloping one way, common on additions, porches, and modern houses. All the water from the whole roof arrives at one edge, so the drainage at that edge is the whole drainage design.
Butterfly roof: Two planes sloping inward to a central valley. Everything drains to the middle, so the internal drain or scupper is a single point of failure and the detailing there is not optional.
Dormer: A framed projection with its own roof and walls set into a slope. Every dormer adds two sidewall lines, a headwall, and usually two valleys — a small dormer can add more flashing to a roof than the rest of the house has.
Cricket: A small false roof built on the up-slope side of a chimney, curb, or other obstruction to split water around it. Also called a saddle. Without one, the up-slope face of a wide chimney collects water, snow, and debris against a flashing joint. Model codes set a chimney width above which a cricket is required; the width and the exceptions belong to the edition adopted locally.
Parapet: A wall extending above the roof surface at the edge. Parapets hide the roof from the street and change the drainage completely: water cannot run off the edge, so it must reach a drain or a scupper through the wall.
Headwall: A wall that meets the roof across the slope, so water runs down the roof and into the wall junction. Headwalls are flashed with a continuous apron; the water arriving is the full width of the plane above.
Sidewall: A wall that meets the roof running with the slope. Sidewalls are flashed course by course with step flashing, not with a single continuous strip, and the bottom of a sidewall needs a kickout.
Slope: Vertical rise per 12 units of horizontal run, written 4:12, 4/12, or “four in twelve”. Slope is what codes, manufacturer instructions, and material limits are written in.
Pitch: In everyday trade use, a synonym for slope. Historically, pitch meant rise divided by the full span — a 6:12 roof on a 24-foot span was “quarter pitch”. Both usages survive, so when a number matters, ask for rise over run in inches per foot rather than assuming which convention someone means.
Rise and run: Rise is the vertical change; run is the horizontal distance it happens over. Roofing states them per 12 inches of run, framing often states them over the whole span, and the two produce different numbers from the same roof.
Pitch factor: The multiplier that converts a horizontal footprint into actual roof surface: for a rise of p inches per 12 inches of run, it is √(1 + (p/12)²). A 6:12 roof has a factor of about 1.118, so a 1,800 sq ft footprint is about 2,012 sq ft of roof. Worked through in full below.
Low slope: Roofs shallower than 2:12. The U.S. Department of Energy’s Building America Solution Center uses that threshold, and it is the line most codes and manufacturer instructions draw as well. Below it, water does not reliably shed off overlapping pieces, so the assembly has to be a sealed membrane rather than shingles. Nothing here is truly flat: a designed slope to drain is still required.
Steep slope: Roofs at 2:12 and above, where overlapping units — shingles, shakes, slate, tile, panels — shed water by gravity. Department of Energy guidance puts the minimum slope for asphalt shingles at 2 in 12, and calls for a doubled underlayment application from 2 in 12 up to 4 in 12. Whether either is enforceable at a particular building is set by the code edition adopted there and by the product’s own instructions — confirm with the authority having jurisdiction.

Group 3 of 12

Layers of a steep-slope assemblySection link

The stack between the framing and the weather, named from the inside out. Most of these are invisible after installation, which is exactly why they get left out of a cheap proposal.

Roof assembly: The whole system — deck, underlayment, insulation and control layers where they are part of the roof, covering, flashings, edges, and fastening — considered together. Fire and wind classifications belong to a tested assembly, not to the visible covering by itself, which is the single most misused idea in roofing marketing.
Roof covering: The outermost weather-facing layer: the shingles, panels, tiles, or membrane. It is the part a homeowner names when they say what kind of roof they have, and roughly the part that shows in a photograph.
Underlayment: The sheet laid over the deck and under the covering. It protects the deck during construction, sheds water that gets past the covering, and in some assemblies is the actual waterproofing layer. Felt, synthetic, and self-adhered products are all underlayments and behave very differently.
Felt: Asphalt-saturated organic or fibreglass underlayment, sold in weights such as #15 and #30. It is the traditional product, it tears more easily when wet or walked on, and the number is a weight class rather than a performance rating.
Synthetic underlayment: A woven or spun polymer sheet used in place of felt. It is lighter, tougher, and usually more slip-resistant to walk on, and its permeability and exposure limits vary enormously by product — this is a case where the manufacturer’s instructions are the specification.
Ice barrier: A self-adhered membrane at the eaves that seals around fasteners and holds back water backed up behind ice. Where a jurisdiction requires one, widely adopted code language calls for it to extend from the eave to a point at least 24 inches inside the interior plane of the exterior wall — which on a low-slope roof with a deep overhang can mean two or three courses of membrane. Whether it is required at all depends on the code edition adopted where the building is and on that jurisdiction’s history of ice forming at the eaves. Confirm with the authority having jurisdiction.
Self-adhered membrane: Any peel-and-stick sheet that bonds directly to the deck and seals around nails. Used at eaves and valleys as an ice barrier, and over the entire deck as a sealed roof deck. Over an unvented or poorly dried assembly, a full-coverage impermeable membrane changes how the deck dries, so it is an assembly decision rather than an upgrade to tick.
Drip edge: Formed metal at the eaves and rakes that carries water clear of the fascia and into the gutter instead of letting it wick backwards onto the wood. It is cheap, it is frequently omitted, and its absence shows up as rotted fascia and stained soffits long before it shows up as a leak.
Starter course: The first course at the eave — a purpose-made strip, or shingles with the tabs removed — that puts a sealed, solid layer under the joints of the first visible course. Guidance developed for the Department of Energy has the starter overhang the drip edge by roughly a quarter to three-quarters of an inch. Skipping it leaves the first course unsealed at exactly the windiest edge.
Field: The main open area of a roof plane, away from edges, penetrations, and transitions. Most of a roof is field; almost none of the leaks are.
Course: One horizontal row of shingles, slates, or tiles. Courses are counted from the eave up, and a repair is described by course and position.
Exposure: The part of each unit left visible to the weather after the course above covers the rest. Exposure is set by the product and the slope, not by preference; for slate, the National Park Service states it directly as the slate length minus the headlap, divided by two. Increasing exposure to stretch material reduces the overlap that does the waterproofing.
Headlap: The vertical overlap between a course and the course two below it — the redundancy that keeps water out when it runs sideways or backs up. Headlap, not the visible surface, is what makes an overlapping roof watertight.
Sidelap: The horizontal overlap between adjacent pieces, panels, or sheets. On metal panels and membrane sheets the sidelap is where the fastening and the seam live, so it is also where a failure usually starts.
Joint offset: How far the joints in one course are shifted from the joints in the course below. Also called the stagger or the bond. The National Park Service records the failure directly for slate: where joints are broken by less than three inches, water can pass between them. Every overlapping material has an equivalent minimum, set by its manufacturer.
Hip and ridge cap: The purpose-made pieces that cover ridges and hips. Cutting field shingles into cap pieces is common and is not always permitted by the product’s instructions — and on a laminated shingle it can crack the piece at the fold.
Granules: The crushed mineral coating on an asphalt shingle. Granules are the shingle’s sunscreen: they shield the asphalt from ultraviolet light and add fire resistance and colour. Losing them locally is normal early shedding; losing them in patches down to the mat is granule loss that has become a service-life question.
Sealant strip: The band of factory adhesive on a shingle that bonds it to the course below once warmed by the sun. Until it seals, a shingle is only a nailed flap. The Insurance Institute for Business & Home Safety states the consequence plainly: the wind resistance of asphalt shingles depends on the sealed shingle resisting the force trying to lift it from the shingle below.
Nailing zone: The narrow band on a shingle where fasteners are required to land, usually where the two laminations overlap. It is product-specific, it is printed on the shingle or its wrapper, and nailing outside it is one of the defects that most reliably voids a manufacturer warranty.

Group 4 of 12

Steep-slope coveringsSection link

The materials that shed water by overlapping. Service-life figures here are planning ranges observed in the field and reported by the cited sources — never a warranty term.

Three-tab shingle: A single-layer asphalt shingle cut into three tabs, giving a flat, repeating pattern. It is the lightest and cheapest asphalt product, and the one most likely to be specified in an insurance scope for a house that originally had it.
Architectural shingle: An asphalt shingle built from two or more laminated layers, giving a thicker profile and a shadow line. Also called laminated or dimensional. The extra laminate is why it is heavier, why the nailing zone is narrower, and why it cannot be cut into ridge caps as freely as a three-tab.
Shingle mat: The reinforcing sheet inside an asphalt shingle, effectively always fibreglass in current North American production. Organic (felt-based) mats were phased out; if a house has them, it is an age indicator, not a product you can match.
Impact-resistant shingle: A shingle built to survive impact, either by adding a reinforcing scrim to the back or by using polymer-modified asphalt for flexibility — both approaches described by the Insurance Institute for Business & Home Safety. It is a laboratory classification, not a hail-proof claim: see UL 2218.
Wood shingle: A tapered wooden roofing unit, historically sawn or split. The National Park Service is explicit that historically all of these were called shingles regardless of how they were made, and that wooden shingle roofs need periodic replacement, lasting from 15 to over 60 years depending on wood, exposure, slope, and ventilation.
Shake: A modern commercial term the industry uses to separate split products from sawn ones — the Park Service notes the word is relatively recent and that no such distinction existed through most of American building history. In practice “shake” now signals a thicker, rougher unit, and on a proposal it should be pinned to a product, a thickness, and a grade rather than left as a look.
Natural slate: Quarried metamorphic stone split into roofing units. The Park Service reports that properly installed slate roofs last 60 to 125 years or longer depending on the slate, the roof configuration, and the location, with some exceeding 200 years. The stone routinely outlives its fasteners and flashings, which is what actually ends the roof.
Standard, textural, and graduated slate: The three historic ways slate roofs were laid: uniform thickness and size; deliberately varied thickness and rough texture; and thickest and largest at the eave grading to thinnest and smallest at the ridge. The distinction matters for matching a repair, and graduated roofs cannot be patched with one stock size.
Clay tile: Fired clay roofing units, made in flat interlocking, S-shaped, and half-cylinder profiles. Density matters more than appearance: the Park Service records that porous, underburned tiles are particularly susceptible to breaking and surface spalling in freeze-thaw cycles, and that water let in through them can rot battens and structure.
Pan and cover tile: The two-piece barrel or mission arrangement: concave pan tiles laid in vertical rows and nailed to the sheathing, with convex cover tiles laid over the joints between them. Knowing which piece is which is how a repair conversation about a tile roof stays specific.
Concrete tile: Cast cement roofing tile, often profiled to resemble clay or wood. It is generally cheaper than clay and comparably heavy, so the structural question is the same one; absorption and freeze-thaw performance vary by product and are worth asking about in cold climates.
Tile underlayment: On most tile roofs the tile is the wearing surface and the underlayment is what actually keeps water out. That is why a tile roof can need a full re-lay with the same tiles reinstalled: the units are sound and the membrane under them is not.
Standing seam: Metal panels joined by raised seams with the fasteners hidden underneath, typically held by clips rather than through-fastened. Department of Energy guidance puts the minimum slope for standing seam systems as low as a quarter unit in 12, against three in 12 for lapped, non-soldered metal roofs without lap sealant — a real functional difference, not a marketing one.
Exposed-fastener panel: Ribbed metal panels screwed through the face with gasketed, colour-matched screws — the Department of Energy describes them as typically three feet wide and 8 to 16 feet long. They cost less than standing seam and carry a maintenance obligation standing seam does not: the gaskets age and the fasteners need periodic inspection.
Stone-coated metal: Pressed steel panels or tiles finished with bonded mineral granules to imitate shingle, shake, or tile. The weight advantage over tile is genuine; the repair-matching problem is real, because profiles and colour lots change.
Architectural metal: Copper, zinc, terne, and lead-coated products, usually formed and soldered by hand rather than roll-formed. They are premium and long-lived, they develop a patina that is part of the specification, and they are unforgiving of contact with incompatible metals — see galvanic corrosion.
Synthetic slate: Moulded polymer or composite units imitating slate or shake. They weigh a fraction of stone and cost far less, and the honest limit is that the field record is decades rather than a century — the long-term claim is a manufacturer projection, not observed service.
Cool roof: A covering chosen for high solar reflectance and thermal emittance. The U.S. Environmental Protection Agency describes both the cooling benefit and the tradeoff: because they reflect sunlight, cool roofs can raise winter energy use in cold climates — a “heating penalty” the EPA says is typically offset by summer savings, but which makes this a climate-dependent choice rather than a universal upgrade.
Solar reflectance: The fraction of sunlight a surface reflects rather than absorbs, on a scale of 0 to 1. Also called albedo. The EPA calls it the most important characteristic in how well a cool roof keeps heat out of a building.
Thermal emittance: How readily a surface releases the heat it has absorbed, also 0 to 1. A surface can be reflective and still run hot if it emits poorly, which is why reflectance and emittance are quoted together.
Solar Reflectance Index (SRI): A single index combining reflectance and emittance so two products can be compared with one number. It is a calculated value under a defined standard and a set of assumed conditions, not a measurement of the roof on your building.

Group 5 of 12

Low-slope and commercial systemsSection link

Below 2:12, water is held out by a continuous sealed surface rather than by overlap. Different physics, different vocabulary, different money — and a residential per-square price does not translate here.

Membrane: The continuous waterproofing sheet or built-up layer on a low-slope roof. Department of Energy guidance groups the families as built-up bitumen, modified bitumen, and single-ply — the last split into thermoplastics such as TPO, PVC and KEE, and thermosets such as EPDM.
Single ply: A membrane installed in one layer of factory-made sheet, seamed on site. It is the dominant commercial approach because it is fast; the tradeoff is that the seams and the attachment carry the entire system.
Thermoplastic: A membrane that softens with heat and can therefore be welded to itself, giving a seam of the same material as the sheet. TPO and PVC are thermoplastics; a hot-air weld is the normal seaming method.
Thermoset: A cured membrane that cannot be re-melted, so seams are made with adhesives or factory-applied tape rather than welded. EPDM is the common thermoset. Seam technology, not the sheet, is where thermoset systems have historically improved.
TPO: Thermoplastic polyolefin: a weldable, usually white single-ply sheet. Formulations have changed repeatedly since introduction, so field record from one decade does not automatically describe the product being quoted now — ask what formulation and thickness the price is based on.
PVC: Polyvinyl chloride single-ply, weldable and notably resistant to grease and many chemicals. It is the usual answer over restaurant kitchens and some industrial exhaust, where a membrane without that resistance degrades early.
KEE: Ketone ethylene ester membrane, a plasticiser chemistry used to keep a thermoplastic sheet flexible over time. Named in Department of Energy guidance alongside TPO and PVC as a thermoplastic option.
EPDM: Ethylene propylene diene monomer, a synthetic rubber single-ply with the longest continuous field record of the modern membranes. Usually black, which is a heat-gain consideration in hot climates and a snow-melt advantage in cold ones.
Modified bitumen: Asphalt modified with polymer and reinforced into rolled sheets, applied in one or two plies. APP is modified for heat application; SBS is modified for flexibility and cold-weather behaviour. Both give redundancy a single sheet does not.
Built-up roof (BUR): Multiple plies of reinforcing felt laid in bitumen and usually surfaced with gravel or a cap sheet. It is the legacy benchmark on institutional buildings: heavy, slow, redundant, and still in service on buildings whose newer neighbours have been re-roofed twice.
Ply: One reinforcing layer within a built-up or modified system. Ply count is a specification item; “four-ply” and “two-ply” are different products at different prices and should never be compared as “a flat roof”.
Spray polyurethane foam (SPF): Foam sprayed in place to form insulation and substrate in one monolithic layer, then protected by a coating. It is seamless and self-flashing, and it carries a recoating obligation: the coating is the wear surface and it is consumable.
Coating: A liquid-applied surface — acrylic, silicone, urethane — rolled or sprayed over an existing roof. Restoration coatings can genuinely extend service life on a sound substrate. Over wet insulation or failed seams, a coating hides the problem rather than fixing it. See core cut.
Fully adhered: The membrane is bonded to the substrate across its whole area with adhesive. It gives a smooth surface and distributes uplift force, and it depends entirely on the substrate being sound, dry, and compatible.
Mechanically attached: The membrane is fastened through to the deck in rows, with the sheet spanning between fastener lines. It is faster and cheaper than adhering and it lets the membrane flutter under wind, which is why fastener spacing and pattern are the design.
Ballasted: The membrane is held down by stone or pavers rather than fastened or glued. It is inexpensive and quiet, and it makes leak location and inspection substantially harder because the surface cannot be seen.
Heat weld: A seam made by melting two thermoplastic sheets together with hot air. A correct weld is one material; a cold weld looks identical from three feet away and fails as a seam.
Seam probe: Running a blunt tool along a finished seam to find unwelded spots. It is the cheapest quality-control step on a single-ply job and the one most often skipped when a crew is behind schedule.
Polyiso: Polyisocyanurate rigid board, the dominant commercial roof insulation. Its R-value per inch is high but temperature-dependent — it performs less well when cold, which matters in exactly the climates where insulation matters most.
Cover board: A thin, dense board between the insulation and the membrane. It gives fasteners something to hold, spreads foot traffic and hail impact, and is one of the first line items removed when a bid is being cut to win.
Tapered insulation: Insulation cut to a slope so a level deck drains. It is how a flat structure gets positive drainage without structural work, and it changes the average R-value of the roof, because thickness varies across the plane. See ponding.
Roof drain: An internal outlet that carries water down through the building. Drains are the primary drainage on most large low-slope roofs, and a blocked one converts rainfall directly into structural load.
Scupper: An opening through a parapet that lets water leave at the edge. Scuppers can be primary drainage or overflow; which one a given scupper is depends on its height above the roof surface.
Overflow drainage: The secondary path — a raised drain or a higher scupper — that carries water when the primary drains are blocked, and that discharges somewhere visible so someone notices. Its whole purpose is to be a nuisance rather than a collapse.
Ponding: Standing water that does not drain. The Asphalt Roofing Manufacturers Association defines ponding water as water that remains on a roof 48 hours or longer, and recommends a minimum quarter-inch-per-foot slope so a roof drains freely. Ponding adds load, accelerates membrane deterioration, grows algae and vegetation, and in freezing climates moves ice across the surface.
Walkway pad: Sacrificial surfacing laid along routes to rooftop equipment. Where there is equipment and no walkway, the membrane is the walkway, and service traffic is a leading cause of punctures on otherwise sound roofs.
Curb: A raised frame that lifts a rooftop unit, skylight, or hatch above the roof surface so it can be flashed properly. Equipment set directly on a membrane without a curb has no correct flashing detail available to it.
Pitch pocket: A small open container filled with sealant around an irregular penetration that cannot be flashed conventionally. Also called a pourable sealer pocket. It is a maintenance item with a service life measured in a few years, not a permanent detail.
Termination bar: A metal strip that clamps the top edge of a membrane against a wall or curb, usually with sealant above it. Where it is loose, missing, or unsealed, water enters behind the membrane and travels — often surfacing far from the entry point.
Edge metal: The formed metal that secures and finishes the perimeter — fascia, coping, gravel stop. Wind pressures are highest at edges and corners, so a failed edge is a common start of a progressive peel that removes the field membrane behind it.
Recover: Installing a new roof over the existing one rather than removing it. Also called an overlay or a roof-over. Adopted codes restrict it — the 2024 Texas Windstorm Insurance Association Building Code, for example, prohibits recover where the existing roof already has two or more applications of any covering, where the existing roof is water-soaked or too deteriorated to serve as a base, and over slate, clay, cement, or asbestos-cement tile. Those are one jurisdiction’s limits at one edition. The limits and exceptions that bind a particular building belong to the edition adopted where it stands; confirm with the authority having jurisdiction.
Tear-off: Removing the existing covering down to the deck. It is the only way the deck gets inspected, it is a large share of the labour and disposal cost, and it is the line item that separates two proposals that look the same. Contrast recover.
Core cut: A small square cut through the whole assembly to see and test what is actually there — how many layers, what insulation, how wet. It is destructive, it is patched immediately, and it is the only way to answer certain questions before a capital decision.
Moisture survey: Infrared, nuclear, or capacitance scanning to map wet insulation without opening the roof. Each method infers moisture from something else — heat retention, hydrogen content, capacitance — so each has false positives, and findings are confirmed with core cuts.

Group 6 of 12

Flashing, edges, and detailsSection link

Where the roof stops being a roof — at a wall, a chimney, a pipe, an edge. Field material rarely leaks. These junctions do, and the words for them are how you tell a thorough proposal from a cheap one.

Flashing: Formed sheet material — metal, membrane, or purpose-made accessory — that carries water across a junction and back onto the roof surface. Sealant is not flashing. Sealant is what you use to finish a flashing detail, and a detail held together by sealant alone has a maintenance interval, not a service life.
Base flashing: The lower half of a two-part detail: the piece that turns up the vertical surface from the roof side. It is installed with the roof, it is under the covering, and it is the part that actually keeps water out.
Counterflashing: The upper half: the piece let into or fastened onto the wall that laps over the base flashing and sheds water onto it. Two overlapping pieces exist so the roof can be replaced without dismantling the wall — a single piece caulked to brick is a repair, not a detail.
Step flashing: Individual L-shaped pieces woven in with each course where a roof plane runs up a sidewall. One piece per course, each lapping the one below. A continuous strip of metal used instead is one of the most common causes of a wall leak that gets blamed on the siding.
Apron flashing: A single continuous piece across a headwall or the down-slope face of a chimney, where water arrives across the full width rather than running alongside. Also called head flashing.
Kickout flashing: A flared piece at the bottom of a step-flashed sidewall that throws water away from the wall and into the gutter. Also called a diverter. It is small, it is frequently missing, and where it is missing the water goes behind the cladding — the resulting damage is inside the wall, not on the roof.
Open valley: A valley lined with metal, with the covering stopping short on either side so water runs on the metal. The National Park Service notes that open valleys are easier to install and maintain and are generally more watertight than closed ones — a judgement made about slate roofs that holds broadly.
Closed valley: A valley where the covering continues across the line, over a continuous lining or flashing built in course by course. It looks cleaner and it is less forgiving: the water is running under the material rather than on a visible surface.
Woven valley: A closed valley in which shingles from both planes alternate across the line. It is fast and it relies entirely on the shingles below staying sealed, so it behaves poorly with stiff laminated shingles and on unequal slopes.
Pipe boot: The flanged collar that seals around a plumbing vent. The flange usually outlives the rubber gasket at its neck by decades, which makes a cracked boot one of the most common single-point leaks on an otherwise sound roof — and one of the cheapest repairs.
Storm collar: A band clamped around a flue or pipe above the flashing to keep water from running down inside it. Small, cheap, and routinely missing after an appliance is serviced.
Reglet: A groove cut or cast into masonry that counterflashing is tucked into and sealed. A properly cut reglet is why a chimney detail survives a roof replacement; surface-mounted counterflashing sealed to the face is the shortcut version.
Curb flashing: The detail that seals a skylight, hatch, or equipment curb to the roof. Manufactured skylights ship with a flashing kit matched to the covering type and slope — using a different kit, or none, is a specification error rather than a workmanship one.
Fascia: The vertical board or metal at the eave that closes the ends of the rafters and normally carries the gutter. Rotted fascia is usually a symptom of a missing drip edge or an overflowing gutter, not of a roof leak.
Soffit: The underside of the roof overhang. In a vented assembly it is where intake air enters, which is why blocking or painting over a vented soffit quietly disables half the ventilation system. See intake vent.
Gutter: The channel at the eave that collects runoff and carries it to downspouts. Undersized or under-pitched gutters overflow at the fascia in heavy rain, and the resulting damage — fascia, soffit, siding, foundation — looks like a roof failure and is not one.
Downspout: The vertical pipe taking gutter water to the ground. Capacity is set by the smallest constriction, so one undersized downspout can make an adequately sized gutter overflow.

Group 7 of 12

Ventilation, air, and moistureSection link

The half of roof performance that happens under the deck. Both vented and correctly designed unvented assemblies are legitimate; what is not legitimate is a universal ratio quoted without the assembly, the climate zone, and the adopted code it belongs to.

Attic: The space between the ceiling of the top storey and the roof deck. Whether it is inside or outside the insulated, air-sealed envelope is the decision that determines nearly everything else about how the roof behaves.
Net free area (NFA): The clear open area of a vent after its screening and slot geometry are taken into account, as described by the Department of Energy’s Building America Solution Center — which also notes that most screened vents have around 60 percent free area. A vent’s NFA is the number that counts toward a ventilation requirement; its outside dimensions are not.
Ventilation ratio: The required net free area expressed as a fraction of the ventilated attic area. Building America Solution Center guidance states 1/300 as the standard requirement where soffit or eave venting is present, and 1/150 for homes without roof overhangs or other accommodation for openings at the soffit or eave. The ratio that applies to a specific building — and the conditions attached to the smaller one — is set by the code edition adopted in that jurisdiction. Confirm with the authority having jurisdiction before designing to a number from any website, including this one.
Intake vent: A low vent, usually in the soffit or at the eave, where outside air enters the attic. Building America Solution Center guidance calls for a lower vent in each rafter bay so air actually moves through the whole roof rather than short-circuiting near one opening.
Exhaust vent: A high vent where air leaves. Department of Energy guidance places no more than 50 percent and no less than 40 percent of the required ventilation area high on the roof — the rest is intake. More exhaust than intake does not ventilate better; it pulls make-up air from wherever it can find it, including the house.
Ridge vent: A continuous exhaust vent along the ridge, over a slot cut in the deck. It is the most even exhaust available because it draws along the whole ridge; it is also the one most often installed without cutting an adequate slot, in which case it ventilates nothing.
Gable vent: A louvred opening in the gable end wall. Mixing gable vents with a ridge vent can short-circuit the intended airflow, so the exhaust openings are usually chosen as one system rather than accumulated over the years.
Powered attic ventilator: A fan that forces air out of the attic. Where the ceiling below is not thoroughly air-sealed, a powered exhaust can draw conditioned — and in the worst case combustion — air out of the house. It is an assembly decision, not an accessory.
Baffle: A rigid channel at the eave holding a clear air path between the insulation and the underside of the deck. Department of Energy guidance calls for a minimum one inch of space between insulation and roof sheathing, with baffles providing both that gap and a barrier keeping insulation out of the vent openings. Without them, blown insulation fills the eave and the intake stops working.
Unvented attic: An assembly insulated at the roof plane, with no ventilation between the insulation and the deck. It is a recognised approach, not a workaround: Department of Energy code-compliance guidance describes air-impermeable insulation applied in direct contact with the underside of the sheathing, and, in colder zones, rigid insulation above the deck sufficient to keep the sheathing’s monthly average temperature above 45°F. Building America guidance notes it can be the better choice in hurricane, wildfire, and hot-humid conditions, where vents admit wind-driven rain or embers.
Vapor diffusion port: A deliberately vapor-open opening near the ridge of an unvented assembly, used in warm climates so moisture can leave by diffusion without ventilating the space. Department of Energy guidance describes it for climate zones 1 to 3 with a permeance of at least 20 perms and a minimum area of 1:600 of the ceiling area.
Air barrier: The continuous layer that stops air moving between inside and outside. Air carries far more moisture into an attic than diffusion does, which is why Department of Energy guidance is explicit that the ceiling be thoroughly air-sealed before insulation goes on top of it — insulation slows heat, it does not stop airflow.
Vapor retarder: A material that limits how much water vapour diffuses through an assembly, classed by permeance: Class I at 0.1 perm or less, Class II above 0.1 and up to 1.0, Class III above 1.0 and up to 10. Which class belongs where depends on climate zone and assembly — a Class I retarder installed on the wrong side of an assembly traps moisture instead of excluding it.
Perm: The unit of water-vapour permeance, measured under ASTM E96. Higher perms mean more vapour passes and the assembly dries more readily; lower perms mean more resistance to vapour moving in — and less ability to dry if it gets in another way.
Dew point: The temperature at which air holds all the moisture it can and starts condensing on the surfaces it touches. Almost every attic moisture problem is the same story: humid indoor air reaching a surface colder than its dew point.
Condensation: Liquid water forming from vapour on a cold surface. Sheathing wet on its underside in winter with no path from above is a condensation problem, not a leak, and adding roof material will not change it.
Thermal bridging: Heat taking a shortcut through a conductive path — rafters, fasteners, metal framing — around the insulation. Thermal bridges show up on a snowy roof as melted stripes over the framing, which is a free diagnostic from the ground.
Stack effect: Warm air rising and pushing out through the top of a building, drawing cold air in at the bottom. It is why leaks in a ceiling plane push conditioned, humid air into an attic all winter, and why air sealing the ceiling matters more than the vent count.
Ice dam: A ridge of ice at a cold eave, formed when heat escaping into the attic melts snow higher up and the meltwater refreezes where the roof is colder. Water then backs up behind the dam and finds its way under the covering. The fix is the heat loss: Department of Energy guidance shows an attic that is thoroughly air-sealed, baffled, and insulated as one unlikely to encourage ice dams. An ice barrier limits the damage; it does not stop the dam forming.
R-value: Resistance to heat flow through a material, per inch or for a whole product. It is measured in still air under laboratory conditions, so installed performance depends on the material being at its rated thickness, uncompressed, and not bypassed by air movement.

Group 8 of 12

Measurement, quantities, and unitsSection link

The units a quote is written in. Getting these straight is the difference between comparing three prices and comparing three unrelated numbers.

Roofing square: 100 square feet of roof surface. It is the trade’s unit of area, and the reason a contractor says “twenty-two squares” rather than “2,200 square feet”. A square is not a square foot and not a square yard; a price quoted per square is 100 times a price quoted per square foot.
Bundle: A packaged unit of shingles. How many bundles make a square depends on the product — commonly three for standard-weight shingles and more for heavy laminates — and the coverage is printed on the wrapper. Never assume the ratio; read the package.
Plan area: The horizontal footprint the roof covers, measured as if looking straight down — including overhangs. It is what satellite tools and site plans give you, and it is always smaller than the roof itself. See pitch factor.
Surface area: The actual sloped area of the roof planes: plan area multiplied by the pitch factor, plane by plane. This is what material and installed price should be calculated on.
Waste factor: The percentage added to measured surface area to cover cuts at hips, valleys, rakes, and starter and cap fabrication. A simple gable needs little; a cut-up roof with several valleys needs much more. Waste is applied once, to order quantity — not silently to the priced area.
Order area: Measured surface area plus waste — the amount of material actually bought. Substituting order area for surface area in a price calculation inflates the job by the waste percentage, which is a quiet way for two quotes to differ without either being wrong on its face. See the worked example.
Takeoff: The measured quantity list a price is built from: areas by plane and pitch, plus linear feet of ridge, hip, valley, eave, rake, and wall. A proposal built from a real takeoff can show these numbers; one built from a windscreen estimate cannot.
Lineal foot: A measurement of length rather than area, used for ridge and hip cap, valley metal, drip edge, gutter, and flashing. Two roofs with identical square counts can differ by hundreds of lineal feet, which is most of what “complexity” means on a bid.
Pounds per square: Installed weight per 100 square feet — the unit a structural conversation about a heavier covering happens in. It is the honest way to compare an asphalt roof with tile or slate, because it converts an aesthetic choice into a dead load an engineer can evaluate for the building.
Mil: One thousandth of an inch, the unit membrane thickness is sold in — 45, 60, 80 mil. Thickness is not the whole story on a single-ply, but comparing a 45-mil price with an 80-mil price as though they were the same roof is a common bidding trap.
Gauge: A numbering system for sheet-metal thickness in which a smaller number means thicker metal. Steel and aluminium gauges are not the same thickness, and metal roofing is sometimes sold by gauge and sometimes by decimal inches — ask which.
Ounce (copper): Copper sheet is specified by the weight of one square foot: 16 oz, 20 oz, 24 oz. Heavier copper costs more and lasts longer at seams and in valleys, and a copper detail quoted without a weight is not a specification.
Coverage: The area one unit of material actually covers after lapping, as opposed to its physical size. Coverage, not sheet size, is what a quantity is calculated from — and it changes if exposure changes.
Complexity: A catch-all for what makes a roof cost more per square: number of planes, valleys and hips, dormers, penetrations, steepness, height, and access. It is not a fudge factor when a proposal itemises what it refers to, and it is when the proposal does not.

Group 9 of 12

Fasteners and attachmentSection link

The layer nobody photographs. Attachment is what determines whether a covering stays on in wind, and almost every fastener term below names a specific way that goes wrong.

Roofing nail: A short, large-headed nail sized to penetrate through the covering and into or through the deck. Length must suit the assembly thickness, and Department of Energy guidance is direct that nails, properly driven, are used rather than staples — with generally six nails per shingle strip in high-wind areas.
Ring-shank nail: A nail with rings rolled into the shank that grip the wood and resist withdrawal. It is the standard answer where uplift matters, including for re-nailing a deck during a re-roof in high-wind regions.
Cap nail: A nail with a plastic or metal washer that spreads the load, used for fastening underlayment. Ordinary staples or bare nails tear through synthetic underlayment in wind before the covering ever goes on.
Fastener pattern: The number and placement of fasteners per unit or per square. It is set by the product’s instructions and by the wind conditions of the site, and it is one of the few workmanship items that is genuinely verifiable from a photograph taken during installation.
Overdriven fastener: A nail driven so hard it cuts into or through the shingle mat, or so deep it dimples a metal panel. It leaves the unit effectively unfastened at that point while looking perfectly normal from the ground.
Underdriven fastener: A nail left proud of the surface. It holds the course above off the one below, telegraphs through as a bump, and eventually wears a hole in the material sitting on it.
Shiner: A fastener that missed the framing or the substrate entirely. From inside an attic they read as a line of bright points catching the light, which is what an inspector is looking at when they report them; shiners are a leak path and an indicator of how carefully the rest of the deck was fastened.
Clip (metal panel): The concealed bracket that holds a standing-seam panel to the deck. A fixed clip pins the panel; a floating clip allows it to move as it heats and cools. Choosing wrong for the panel length is how a metal roof oil-cans, tears at fasteners, or buckles.
Gasketed screw: A screw with a bonded washer used on exposed-fastener panels. The washer is the waterproofing, it is a consumable, and re-torquing or replacing screws is a real maintenance obligation on this kind of roof — one that is rarely mentioned at the point of sale.
Insulation plate: The metal or plastic disc under a fastener that spreads load across rigid insulation on a low-slope roof. Fastener and plate density, in a defined pattern with increased density at perimeters and corners, is what an uplift specification is made of.
Induction welding: Bonding a single-ply membrane to coated plates underneath by heating the plates through the sheet. It attaches the membrane without penetrating it, which removes the fastener-through-membrane failure mode and adds a new dependency on plate placement.
Uplift resistance: How much suction the assembly can take before it comes off. Wind does not push a roof off; low pressure above it pulls, hardest at edges and corners. UL Solutions lists uplift testing under standards including UL 580 and UL 1897 — and the result belongs to the tested assembly, not to a product on its own.
Pull-through: A failure where the fastener stays in place and the material tears over its head. It is the reason plates and washers exist, and the reason fastener count alone does not describe an attachment.
Galvanic corrosion: Accelerated corrosion when two dissimilar metals are in contact with moisture present — copper against aluminium or bare steel, for example. It is why a copper detail must not drain onto a steel one, and why fastener metal is specified to match the roofing metal.
Fastener metal: Which alloy the nails or screws are. The National Park Service states it plainly for slate: non-ferrous nails such as solid copper or stainless should always be used, because plain steel and galvanized nails usually rust out long before the slate does. Same logic, all long-life materials.
Deck re-nailing: Adding fasteners to existing sheathing while the deck is exposed during a tear-off. It is one of the few genuinely high-value upgrades available only at that moment, and it is priced as a separate line item or not done.

Group 10 of 12

Damage, wear, and failure modesSection link

What people are usually looking a word up for. Several of these describe normal ageing, several describe a covering at the end of its service, and telling them apart is most of the value of knowing the vocabulary.

Granule loss: Loss of the mineral surfacing from an asphalt shingle. A little in the gutter after installation is manufacturing excess. Bare patches showing the mat, across whole slopes, mean the asphalt is now exposed to ultraviolet light and the shingle is in its last phase. See granules.
Curling: Shingle edges lifting away from the roof as the mat shrinks and the asphalt hardens. Curled edges catch wind, so a curled roof usually starts losing pieces in the first serious storm after the curling becomes obvious.
Cupping: The centre of a unit hollowing while the edges lift — common on wood and on shingles over a hot, poorly ventilated deck. It is a symptom pointing under the deck as often as at the covering.
Clawing: The reverse pattern: the middle of the shingle lifts while the edges stay down. Like curling, it indicates the mat and asphalt have aged past flexible, and it is usually seen across a whole plane rather than in one spot.
Blistering: Raised bubbles in a shingle or a membrane, from moisture or trapped gas expanding under heat. Intact blisters are cosmetic; blisters that have opened have exposed the layer below and become an entry point.
Thermal splitting: Straight cracks that open as material contracts in cold, most often across a membrane at a deck joint or in an aged shingle. The give-away is that the split is straighter than any impact damage.
Creased shingle: A shingle lifted by wind hard enough to fold, then dropped back into place. It looks attached from the ground and is broken through the mat along the crease. Creasing is the wind damage most often missed on a walk-around and most often argued about with an adjuster.
Blow-off: Loss of covering to wind. It normally starts at an edge, a corner, or a previously damaged spot rather than in the field, and it propagates once the first unit is gone. Unsealed sealant strips — from cold-weather installation, dust, or a shingle laid over a bad surface — are a common precondition.
Nail pop: A fastener backing out and pushing up the material above it, from framing movement, seasonal humidity, or a nail that was never fully seated. On a shingle roof it eventually wears a hole in the piece it lifts.
Delamination: Layers separating: the two laminations of a shingle coming apart, plies of a deck panel separating after wetting, or — as the National Park Service describes for slate — paper-thin laminations flaking off until the stone goes soft and spongy.
Nail sickness: A trade term for a slate or tile roof whose units are sound but whose fasteners have corroded, so pieces slip out one after another. The Park Service documents the mechanism without the nickname: rusting nineteenth-century cut nails are a common cause of slate loss on historic roofs. The repair is a full re-lay, not a patch — which is why the diagnosis matters so much financially.
Spalling: Surface flaking from freeze-thaw cycling in a porous material. The Park Service links it to underburning in clay tile — porous tiles are particularly susceptible to breaking and exterior surface spalling — and the same absorption question decides whether a given tile or slate belongs in a freeze-thaw climate at all.
Alligatoring: The cracked, scaled pattern that forms in exposed bitumen as it oxidises, named for what it looks like. It signals surfacing loss on a built-up roof rather than an immediate leak, and it is a maintenance trigger.
Fishmouth: An open, lipped gap along a lap in a membrane or a felt, where the sheet was not fully bonded or was laid over a wrinkle. It is a seam failure with a shape, and it is repairable if found before water has run in it for a season.
Hail bruise: A soft spot where impact has fractured the mat under the surfacing without necessarily breaking through. It is found by feel rather than by eye, which is why hail assessment is done by someone qualified and not from a photograph.
Spatter mark: The clean spot left where hail knocked the oxidation off a metal surface — vents, flashings, gutters. Spatter marks establish that hail of some size fell; they do not by themselves establish that the covering was functionally damaged.
Functional vs cosmetic damage: Functional damage shortens the life of the assembly or lets water in; cosmetic damage changes how it looks. The distinction drives insurance outcomes, it is frequently disputed, and it is decided by inspection of the actual roof rather than by a rule.
Moss, algae, and lichen: Three different growths often lumped together. Dark streaking is algal and is largely cosmetic; moss holds water against the surface and lifts units, so it is a maintenance problem; lichen bonds into the surfacing and cannot be removed without taking granules with it. Pressure washing an asphalt roof to remove any of them removes the granules too.
Punky decking: Sheathing that has been wet long enough to lose strength — soft, spongy, and unable to hold a fastener. It is usually discovered at tear-off, which is why a written deck-replacement allowance and unit price belongs in the contract before work starts.
Water travel: The distance between where water enters a roof and where it appears inside. Water follows framing, wiring, and the underside of the deck before it drops, so a stain is a starting point for investigation rather than a location.

Group 11 of 12

Contract, quote, and insurance vocabularySection link

The words that decide who pays. These are definitions of terms, not legal advice: what any of them means for a specific document, claim, or dispute depends on that document and on the law where the property is.

Scope of work: The written description of exactly what will be done — layers removed, deck treatment, underlayment product, flashing replaced or reused, edges, ventilation, disposal, permits, cleanup. Price without scope is not comparable to anything. This is the whole reason a quote checklist exists.
Allowance: A sum carried in the contract for work whose quantity is not known yet — most often deck replacement. A real allowance states a unit price and a quantity included, so both parties know what happens when the actual number differs.
Unit price: The agreed price per unit for a defined extra — per sheet of decking, per lineal foot of fascia, per pipe boot. Unit prices set in advance are what keep a mid-project discovery from becoming a negotiation on a torn-off roof.
Change order: A written amendment adding, removing, or altering work and stating the price effect, signed before the work happens. Verbal change orders are the origin of most residential roofing disputes.
Retainage: A portion of the price held back until completion or until punch-list items are closed. Common on commercial contracts, less so on residential, and worth understanding before agreeing to a payment schedule either way.
Punch list: The itemised list of remaining or defective work agreed at walkthrough. On a roof it usually includes magnet sweeps for nails, landscaping and gutter cleanup, sealant touch-ups, and documentation not yet handed over.
Mechanic’s lien: A legal claim a contractor or supplier can record against a property for unpaid work or materials. The rules — who may file, deadlines, notice requirements, and how a lien is released — vary substantially by state, and this page cannot tell you what they are where you live.
Lien waiver: A document in which a contractor or supplier gives up lien rights for work already paid for. Whether a waiver is conditional or unconditional, and on what it operates, is set by the document and the applicable state law.
Certificate of insurance: A summary document evidencing a contractor’s general liability and workers’ compensation coverage. It is evidence of a policy on a date, not a guarantee of coverage for your project — which is why verification comes from the insurer named on it, not from the paper.
Workmanship warranty: The installer’s own promise to fix defects in how the work was done. It is worth exactly as much as the company standing behind it, so its length is far less informative than the company’s age, insurance, and complaint history.
Prorated warranty: A warranty whose payable value declines over time, typically after an initial full-value period. A long headline number is often mostly prorated years, in which case the later coverage is a discount on materials rather than a replacement.
Transferability: Whether a warranty passes to the next owner, usually once, within a stated window, sometimes for a fee and with a registration step. If nobody registers the product after installation, the question is often moot.
NDL warranty: No dollar limit: a commercial warranty in which the manufacturer covers repair cost without a cap tied to the original material price. NDL coverage normally requires an approved installer, an approved assembly, and documented maintenance and inspections.
Exclusion: What a warranty or policy explicitly does not cover — commonly ponding water, foot traffic, chemical exposure, alterations by others, and consequential damage. The exclusions are where a warranty is actually defined.
Actual cash value (ACV): Replacement cost less depreciation for age and condition. An ACV settlement on a fifteen-year-old roof can be a fraction of what replacing it costs, and how depreciation is calculated is set by the policy.
Replacement cost value (RCV): The cost to replace with like kind and quality without deduction for depreciation, typically paid in stages — an initial ACV payment, with the balance released after the work is done and documented.
Recoverable depreciation: The withheld portion of an RCV claim that becomes payable once the work is completed and invoiced. Whether it is recoverable, and by when, is a policy term, not a general rule.
Supplement: A request to an insurer for additional payment when the work required exceeds the original scope — code-required items, hidden deck damage, quantities that were understated. Supplements for work genuinely required are ordinary. A supplement invented so a contractor can absorb a policyholder’s deductible is a misstatement of the price of the work, and how that is treated is a legal question in the state where the property is.
Assignment of benefits (AOB): An agreement transferring a policyholder’s claim rights to a contractor so they can bill and negotiate with the insurer directly. Several states have restricted or regulated the practice; whether one is enforceable, revocable, or advisable where you live is a legal question.
Deductible: The amount a policyholder pays before coverage applies. Wind and hail deductibles are often a percentage of the insured value rather than a flat sum, which can be several times larger. An offer to “cover your deductible” is a proposal to misstate the price of the work.

Group 12 of 12

Code, testing, and listing termsSection link

The most misused vocabulary in roofing sales. There is no nationwide building code for ordinary site-built construction — states and local governments adopt and amend model codes — so every term here has a jurisdiction attached to it.

Authority having jurisdiction (AHJ): The office that actually enforces building requirements for a specific property — usually a municipal or county building department, sometimes a state agency. The AHJ decides which edition applies, what local amendments change, what a permit covers, and what an inspector will accept. Every code statement on this site defers to it.
Model code: A published code written to be adopted, not a law in itself. The International Residential Code and International Building Code are model codes; they become enforceable only where a jurisdiction adopts a particular edition, usually with amendments.
Adopted edition: The specific year of a model code a jurisdiction has put into force, together with its local amendments and effective date. Two neighbouring towns can be on different editions, so a requirement cited without an edition and a jurisdiction is not a requirement.
Statewide code: Some states adopt one code applying everywhere, enforced locally — Virginia’s Uniform Statewide Building Code, for example, is based on nationally accepted model codes with state amendments, and its enforcement is the responsibility of each local government’s building inspections department. Other states leave adoption to local governments entirely.
Permit: Authorisation from the AHJ to perform the work, normally with inspections attached. Who pulls it, what triggers it, and what it costs are local. Unpermitted work is a resale and insurance problem long after it is a code problem.
Climate zone: The energy-code classification of a location, with a moisture designation attached. Insulation, vapour control, and unvented-assembly requirements are written by zone, which is why zone predicts roofing decisions better than a state line does.
Tested assembly: A specific combination of deck, underlayment, insulation, covering, and fastening that was tested together and listed as a unit. Substituting any component can invalidate the result, which is the reason a classification cannot be read off a single product.
Listing: A published entry from a certification body recording that a specific assembly or product met a specific standard. A listing is checkable by number; a marketing claim of being “rated” is not.
Fire class (A, B, C): A roof covering’s fire classification, determined by the tests in UL 790 and ASTM E108 — spread of flame, intermittent flame, and burning brand — which UL Solutions lists as its fire tests of roof coverings. The classification belongs to a tested assembly, not to the covering in isolation: underlayment and deck conditions can change the result. A shingle sold as “Class A” achieves that class in the assemblies it was tested in.
UL 2218: The impact-resistance test for prepared roof covering materials, producing Class 1 through Class 4 by dropping steel balls of increasing size; the Insurance Institute for Business & Home Safety describes Class 4 products as tested with balls of 2.00 inches. Class 4 does not mean hail proof. The pass criterion is a breach seen from the back of the specimen, whereas IBHS evaluates hail performance across three damage modes including deformation and granule loss — the damage a homeowner and an adjuster actually look at.
ASTM D3161: A fan-induced wind test for asphalt shingles, with classes including D and F in ascending order. It is a laboratory classification of a product under defined conditions, not a statement about the wind at a building.
ASTM D7158: A wind test based on the uplift of sealed shingles, with classes D, G and H in ascending order. Adopted codes map these classes to design wind speeds: the 2020 Florida Building Code — Residential, 7th edition, for example, accepts D3161 Class D or D7158 Class G where Vasd is 100 mph or less, and D3161 Class F, TAS 107, or D7158 Class H for all wind speeds. That mapping is Florida’s, at that edition; it is not the rule anywhere else, and the edition in force where you live is a question for the authority having jurisdiction. See basic wind speed.
Wind uplift test: Laboratory testing of how much uplift pressure an assembly resists — UL Solutions lists standards including UL 580 and UL 1897. Results are expressed for the tested assembly at a tested fastening density; they are not a wind-speed rating for a building. See uplift resistance.
FM Approval: An assembly-level listing widely specified on commercial buildings, covering wind uplift along with fire and, for some listings, hail. As with every listing, the approval describes the assembly as tested — deck type, insulation, fastening pattern, and membrane together.
Basic wind speed: The mapped design wind speed for a site, used with exposure category, building height and geometry, risk category, enclosure, and pressure zone to derive the actual design pressures. A marketing “mph rating” on a product is not a code determination and does not account for any of those variables.
Pressure zone: The division of a roof into field, perimeter, and corner areas, because suction is far higher at the edges and corners than in the middle. It is why attachment density increases toward the perimeter and why edge failures start there.
Product approval: A state or local system requiring products to be evaluated and listed before use — Florida’s statewide product approval and Miami-Dade’s Notice of Acceptance are the best-known, and their test standards, such as TAS 107, appear directly in adopted code text. Approval is jurisdiction-specific by design.
Sealed roof deck: Sealing the deck itself — with a full self-adhered membrane, taped sheathing seams, or a two-layer felt system — so that water is kept out even if the covering is lost. The Insurance Institute for Business & Home Safety requires it in its FORTIFIED roofing standard, and the same three options appear in Department of Energy guidance. Also called a secondary water barrier.
Asbestos-containing material: Older shingles, felts, mastics, and cement products may contain asbestos. The U.S. Environmental Protection Agency states that the only way to be sure whether a material contains asbestos is to have it tested by a qualified laboratory, recommends testing when suspect material is damaged or when planned work would disturb it, and says samples should be taken by a properly trained and accredited asbestos professional. Do not sand, scrape, break, or sweep suspect material.
Fall protection: The systems that stop a worker falling from a roof. OSHA requires workers in residential construction six feet or more above lower levels to be protected by conventional fall protection — guardrails, safety nets, or personal fall arrest — and states that falls are the leading cause of death for workers in residential construction. That is the standard for trained, equipped professionals, which is the clearest possible answer to whether an untrained homeowner should be on a roof.

Worked example

One roof, taken through every unit on this pageSection link

A simple gable, 1,800 square feet of footprint measured to the edge of the eaves, both planes at 6:12, ventilated attic with a flat ceiling below it. Nothing here is a price; it is the arithmetic that turns a building into the quantities a proposal is written in.

Step 1 — from footprint to order quantity. Every figure is derived from the two inputs stated above; no cost data is involved.
Step	Input	Arithmetic	Result
1. Plan area	Footprint measured to the eave edge	—	1,800 sq ft
2. Pitch factor	6:12 slope	√(1 + (6/12)²) = √1.25	1.118
3. Roof surface area	Plan area × pitch factor	1,800 × 1.118	2,012 sq ft
4. Roofing squares	Surface ÷ 100	2,012 ÷ 100	20.1 squares
5. Order area	Surface + 12% waste, for a simple gable	2,012 × 1.12	2,254 sq ft — 22.5 squares
6. Bundles	Product coverage, read off the wrapper	22.5 × 3 bundles per square	68 bundles, if this product is three to a square

Read this table one item at a time

1. Plan area

Input: Footprint measured to the eave edge
Arithmetic: —
Result: 1,800 sq ft

2. Pitch factor

Input: 6:12 slope
Arithmetic: √(1 + (6/12)²) = √1.25
Result: 1.118

3. Roof surface area

Input: Plan area × pitch factor
Arithmetic: 1,800 × 1.118
Result: 2,012 sq ft

4. Roofing squares

Input: Surface ÷ 100
Arithmetic: 2,012 ÷ 100
Result: 20.1 squares

5. Order area

Input: Surface + 12% waste, for a simple gable
Arithmetic: 2,012 × 1.12
Result: 2,254 sq ft — 22.5 squares

6. Bundles

Input: Product coverage, read off the wrapper
Arithmetic: 22.5 × 3 bundles per square
Result: 68 bundles, if this product is three to a square

Waste is applied once, to the quantity ordered. If a proposal applies the same unit price to order area instead of measured surface area, this roof costs 12 percent more — about 2.4 squares — without a single line of the scope changing.

Step 2 — the same building, in ventilation units. Illustrative only: the ratio that applies to a real attic is set by the code edition adopted in its jurisdiction.
Step	Input	Arithmetic	Result
1. Ventilated area	Flat ceiling below the attic	—	1,800 sq ft
2. Required net free area	1/300, where soffit or eave venting is present	1,800 ÷ 300	6.0 sq ft — 864 sq in
3. Exhaust share	40–50% of the requirement placed high	864 × 0.40 to 0.50	346–432 sq in
4. Intake share	The remainder, low at the eaves	864 − exhaust	432–518 sq in
5. Ridge vent length	A product publishing 18 sq in of NFA per lineal foot	432 ÷ 18	24 lineal feet of ridge
6. Soffit vent count	16 × 8 in vents, 128 sq in gross, roughly 60% free area	432–518 ÷ ~77	Six or seven vents, distributed along the eaves

Read this table one item at a time

1. Ventilated area

Input: Flat ceiling below the attic
Arithmetic: —
Result: 1,800 sq ft

2. Required net free area

Input: 1/300, where soffit or eave venting is present
Arithmetic: 1,800 ÷ 300
Result: 6.0 sq ft — 864 sq in

3. Exhaust share

Input: 40–50% of the requirement placed high
Arithmetic: 864 × 0.40 to 0.50
Result: 346–432 sq in

4. Intake share

Input: The remainder, low at the eaves
Arithmetic: 864 − exhaust
Result: 432–518 sq in

5. Ridge vent length

Input: A product publishing 18 sq in of NFA per lineal foot
Arithmetic: 432 ÷ 18
Result: 24 lineal feet of ridge

6. Soffit vent count

Input: 16 × 8 in vents, 128 sq in gross, roughly 60% free area
Arithmetic: 432–518 ÷ ~77
Result: Six or seven vents, distributed along the eaves

Every product figure here is read from that product’s data sheet, not from this page. If the applicable ratio is 1/150 rather than 1/300, every number in this table doubles — and a correctly designed unvented attic answers the same problem a different way.

Considerations

The guardrails these words come withSection link

Five terms in this glossary are routinely used to claim more than they can support. Here is the limit on each, stated once so the entries above do not have to repeat it.

Fire: Class A, B, and C describe performance in the roof-covering fire tests of UL 790 and ASTM E108. The classification is earned by the combination that was tested.
A fire classification applies to a tested assembly — deck, underlayment, and covering together — not to a covering in isolation. Substituting a component can change the class the roof actually has.
Wind: Shingle wind classes under ASTM D3161 and D7158, and uplift results under UL 580 and UL 1897, are laboratory outcomes for a product or an assembly under defined conditions. An adopted code is what maps them to a design wind speed for a location.
Wind performance is site- and building-specific. Basic wind speed, exposure, height, geometry, pressure zone, enclosure, risk category, attachment, and the tested assembly all matter; a marketing “mph rating” is not a code determination.
Hail and impact: UL 2218 classes come from dropping steel balls of increasing size and looking for a breach on the back of the specimen. IBHS assesses hail performance across deformation, granule loss, and breaches — the three things people see on a real roof.
“Class 4 impact resistant” does not mean hail proof. It means a specimen survived a defined laboratory impact, judged on a criterion that does not include the denting and granule loss an adjuster inspects.
Moisture and ventilation: Ventilation ratios, ice-barrier extent, insulation levels, and unvented-assembly rules all come from the code edition adopted where the building is, and they interact with climate zone and the assembly itself.
Vented and correctly designed unvented attics are both legitimate. There is no universal ratio and no universal rule: more ventilation is not automatically better, and a number published anywhere — including here — is not a determination for your building.
Code and jurisdiction: There is no nationwide building code for ordinary site-built construction. States and local governments adopt model codes, amend them, and set their own effective dates, and enforcement is usually local even where adoption is statewide.
A reference to model IRC or IBC text is a citation to a model provision, not to the law where you live. Confirm the adopted edition, the local amendments, and the effective date with the authority having jurisdiction before acting on any code term on this page.
Older materials and asbestos: Roofing shingles, felts, mastics, and cement products made before about 1990 may contain asbestos. The EPA recommends testing suspect material when it is damaged or when planned work would disturb it, and says sampling should be done by a properly trained and accredited professional.
Do not sand, scrape, break, or sweep suspect material to identify it. Identification is a laboratory result, not a visual one.

Warranty and repair

Three warranty words that are not interchangeableSection link

The vocabulary in group 11 defines individual terms. These are the three families those terms belong to, because most confusion about roofing warranties is confusion about which one is being discussed.

Manufacturer material warranty: Covers the product against defined defects, usually with a prorated remedy after an initial period, and typically excludes installation error — which is the cause of most roof failures. Registration and transfer conditions are set by the document.
Workmanship warranty: The installer’s promise about how the work was done. Its value depends entirely on the company still existing and still answering the phone, so its length says less than the company’s history, insurance, and complaint record do.
System or NDL warranty: A manufacturer warranty covering an approved assembly installed by an approved contractor, more common on commercial low-slope work. It normally carries obligations of its own: documented maintenance, periodic inspections, and approval before anyone penetrates the roof.

Repairability

Vocabulary also decides whether a roof can be repaired. A discontinued profile, an unmatched colour lot, a graduated slate roof, or a tile with no current equivalent all turn a small repair into a conversation about a slope or the whole roof. When a covering is chosen, the availability of matching pieces in ten years is a real selection criterion, and almost nobody asks about it.

A warranty is a contract between a reader and whoever wrote it. What it covers, what voids it, whether it transfers, and how it is enforced are set by that document and by the law where the reader lives. Read the actual warranty for the product and the installer in front of you — not a summary of one, including this one.

Ask before you sign

Questions that use this vocabularySection link

Each of these asks for something specific enough that a vague answer is itself the answer.

Which of these is in the price: drip edge, starter course, ice barrier, underlayment type, valley method, hip and ridge cap, pipe boots, step flashing, and counterflashing?
Every one of them is a separate material with a separate cost. A proposal that names them is comparable to another proposal that names them; one that says “new roof, complete” is comparable to nothing.
Is your price per roofing square of measured surface area, or per square of order area including waste?
On the worked example above, the same unit price differs by 12 percent depending on the answer. Both approaches exist; only one of them is what the other bidder quoted.
What is the deck allowance — how many sheets are included, and what is the unit price after that?
Deck condition is unknown until tear-off. A stated allowance and unit price turns the most common mid-project surprise into arithmetic instead of a negotiation.
Are the flashings being replaced or reused, and which ones? Is there a cricket behind the chimney?
Reused base flashing under a new covering means the roof’s most failure-prone parts are as old as the roof you are removing. The cricket question tells you whether they looked at the chimney at all.
What ventilation does this roof have now, what will it have when you are done, and what is the intake?
Exhaust is easy to add and intake is easy to forget. An answer that names only a ridge vent has described half a system.
Which assembly is the fire classification and the wind class based on, and can you show me the listing?
A specific answer names an assembly and a listing number. A general answer — “it is Class A” or “they are 130 mile-an-hour shingles” — is the marketing claim this page exists to unpick.

Require these in writing

Number of existing layers to be removed, and disposal included
Underlayment product and where each type is used, by area
Ice barrier product and its extent in feet from the eave, where required
Fastener type, length, and count per unit
Flashing locations, metal, and gauge — replaced or reused, stated per location
Ventilation: intake and exhaust products, quantities, and published net free area
Deck allowance in sheets, plus the unit price beyond it
Permit responsibility and cost
Written warranty documents — manufacturer and workmanship — provided before signing

What goes wrong

Six things the vocabulary is used to imply, and what is trueSection link

Common misconceptions

Common belief
A 30-year shingle lasts 30 years.
What is actually true
It is a warranty term describing a limited, usually prorated remedy — not a service-life prediction. Service life is a planning range set by ventilation, slope, exposure, colour, installation quality, and climate. The same product on two houses in one street can differ by a decade.
Common belief
This shingle is Class A, so the roof is Class A.
What is actually true
Fire classifications are earned by tested assemblies. The deck and underlayment participate, and a shingle marketed as Class A holds that class in the assemblies it was tested in. Ask which assembly and ask for the listing.
Common belief
Class 4 shingles mean no more hail damage.
What is actually true
UL 2218 Class 4 means a specimen resisted a defined steel-ball impact without a breach visible from the back. IBHS evaluates deformation and granule loss as well, and those are what you and an adjuster will be looking at. An insurance discount for Class 4 is a discount, not a guarantee.
Common belief
More attic ventilation is always better.
What is actually true
Ventilation works as a balanced system, and unbalanced exhaust pulls make-up air from wherever it can get it, including the house. Correctly designed unvented assemblies are a recognised approach, and Department of Energy guidance says an unvented conditioned attic may be advisable in coastal, hurricane, wildfire, and hot-humid conditions, where vents let in wind-driven rain or embers.
Common belief
The leak is where the stain is.
What is actually true
Water follows framing, fasteners, wiring, and the underside of the deck before it drops. A stain marks where water finally left the structure. That is why diagnosis starts up-slope of the stain and why a single photograph rarely settles it.
Common belief
A roof-over saves the cost of a tear-off with no downside.
What is actually true
It also removes the only opportunity to see the deck, adds weight, and can shorten the new covering’s life by trapping heat. Adopted codes restrict it, and the restrictions vary by edition: one adopted code prohibits recover where two or more coverings are already present, where the existing roof is water-soaked or too deteriorated to serve as a base, and over slate, clay, cement, or asbestos-cement tile. What binds a particular building is the edition adopted where it stands.

Sources and further readingSection link

Understanding Roofing

Scope and limitations

It cannot tell you what is required at your property.
Every code term here defers to the edition adopted in your jurisdiction and to the authority having jurisdiction.
It cannot interpret your warranty, your contract, or your insurance policy.
Those documents, and the law where the property is, decide what their words mean.
It cannot diagnose a roof.
Several entries describe how a failure looks; none of them can tell you what is happening on a specific building without an inspection.
It carries no cost figures, because a glossary is not the right place for numbers that need a scope, a geography, an as-of date, and a confidence statement attached.
Service-life figures quoted here are observations reported by the cited sources for the materials described, not warranty terms and not predictions for any particular roof.

Asphalt Shingle Roofs — resource guide
U.S. Department of Energy, Building America Solution Center
Layer order and the terms for it: sealed deck options, ice-barrier extent of at least 24 inches inside the interior plane of the exterior wall, drip edge at eaves and rakes, starter strip overhang of a quarter to three-quarters of an inch, the 2:12 minimum slope for asphalt shingles with a doubled underlayment application from 2:12 up to 4:12, and nails rather than staples with generally six per strip in high-wind areas.
Describes good practice and cites model code language; it is not the adopted code in any jurisdiction.
Low-Slope (Flat) Roofs — resource guide
U.S. Department of Energy, Building America Solution Center
The low-slope threshold of less than 2:12, and the membrane families named in this glossary: built-up bitumen, modified bitumen, and single-ply thermoplastics (TPO, PVC, KEE) and thermosets (EPDM).
Metal Roofs — resource guide
U.S. Department of Energy, Building America Solution Center
Exposed-fastener panels as roughly three feet wide by 8 to 16 feet long with gasketed screws; standing seam as concealed-fastener panels held by corrosion-resistant clips; minimum slopes of three units in 12 for lapped non-soldered metal without lap sealant and a quarter unit in 12 for standing seam.
Slope figures are stated as general guidance; a specific product’s instructions govern its own installation.
Calculating Attic Passive Ventilation
U.S. Department of Energy, Building America Solution Center
The definition of net free ventilating area; the 1/300 and 1/150 ratios and when each is described as applying; no more than 50 percent and no less than 40 percent of the required area placed high on the roof; a lower vent in each rafter bay; and most screened vents having roughly 60 percent free area.
Cites the 2015 IRC. The ratio, and the conditions attached to it, belong to the code edition adopted in a given jurisdiction.
Vented versus Unvented Attic
U.S. Department of Energy, Building America Solution Center
That both vented and unvented attics are acceptable approaches, that the choice depends on climate zone, equipment location, complexity and cost, and that unvented conditioned attics may be advisable in coastal, hurricane, wildfire, and hot-humid conditions.
Controlling Moisture in Unvented Attics — code compliance brief
U.S. Department of Energy, Building America Solution Center
Unvented attic requirements as written in IRC Section R806.5: air-impermeable insulation in direct contact with the underside of the sheathing, rigid insulation above the deck sufficient to keep the sheathing’s monthly average temperature above 45°F, and the vapor diffusion port for climate zones 1–3 at 20 perms or more and a minimum 1:600 of ceiling area.
Summarises model IRC provisions. What applies at a property is the edition adopted there.
Class I Vapor Retarders Not Installed in Above-Grade Walls in Warm-Humid Climate
U.S. Department of Energy, Building America Solution Center
Vapor retarder classes by permeance — Class I at 0.1 perm or less, Class II above 0.1 up to 1.0, Class III above 1.0 up to 10 — and permeance measured under ASTM E96.
Air Sealing and Insulating Ceilings in Vented Attics
U.S. Department of Energy, Building America Solution Center
Air sealing the ceiling plane before insulating, baffles in each rafter bay with a minimum one inch of clearance to the sheathing, and an attic built that way being unlikely to encourage ice dams.
How do I know if I have asbestos in my home? (floor tile, ceiling tile, shingles, siding, etc.)
U.S. Environmental Protection Agency
That the only way to be sure a material contains asbestos is laboratory testing; that EPA recommends testing suspect materials when damaged or when planned work would disturb them; and that samples should be taken by a properly trained and accredited asbestos professional.
Using Cool Roofs to Reduce Heat Islands
U.S. Environmental Protection Agency
Solar reflectance (albedo) as the most important cool-roof characteristic, thermal emittance as the supporting one, and the winter heating penalty in cold climates that EPA says is typically — not always — offset by summer cooling savings.
Fall Protection in Residential Construction — guidance
U.S. Occupational Safety and Health Administration
That workers in residential construction six feet or more above lower levels must be protected by conventional fall protection, and that falls are the leading cause of death for workers in residential construction.
An employer obligation for construction work. It is cited here as evidence of the hazard, not as a rule that applies to a homeowner.
Preservation Brief 19: The Repair and Replacement of Historic Wooden Shingle Roofs
U.S. National Park Service
That historically all wooden roofing units were called shingles whether split or sawn, that “shake” is a relatively recent commercial distinction, and that wooden shingle roofs last from 15 to over 60 years depending on wood, exposure, slope, and ventilation.
Written for historic buildings. Service-life figures are observations, not warranty terms or predictions for a specific roof.
Preservation Brief 29: The Repair, Replacement, and Maintenance of Historic Slate Roofs
U.S. National Park Service
Exposure calculated as slate length minus headlap divided by two; standard, textural, and graduated slate roofs; open versus closed valleys and open valleys generally being more watertight; joints broken by less than three inches letting water through; delamination as a failure mode; non-ferrous nails because plain steel and galvanized nails rust out first, with rusting cut nails a common cause of slate loss; and a 60-to-125-year planning range for slate.
Historic-building guidance, not a code determination and not a specification for new construction.
Preservation Brief 30: The Preservation and Repair of Historic Clay Tile Roofs
U.S. National Park Service
Pan and cover tile terminology, tiles laid over battens, corrosion-resistant fasteners and flashings, the need to remove and re-lay all tiles when the fastening system fails, and porous underburned tiles being particularly susceptible to breaking and surface spalling in freeze-thaw cycles.
Historic-building guidance; product-specific behaviour varies.
Roofing Testing and Certification Services
UL Solutions
That fire tests of roof coverings — spread of flame, intermittent flaming, and burning brand — are conducted under UL 790 and ASTM E108, that impact testing is conducted under UL 2218, and that wind uplift testing is conducted under standards including UL 580 and UL 1897.
A services page, not the standards themselves. The standards are purchasable documents; specific pass criteria should be read there or in a listing.
Roof 101
Insurance Institute for Business & Home Safety (IBHS)
Impact-resistant shingles built either with a reinforcing scrim or with polymer-modified asphalt; Class 4 products tested with 2.00-inch balls; IBHS hail ratings assessing deformation, granule loss, and breaches; the wind resistance of asphalt shingles depending on the sealed shingle resisting uplift from the course below; and the sealed roof deck requirement in the FORTIFIED standard.
A standards-and-research body funded by property insurers. Its FORTIFIED requirements are a voluntary programme, not a building code.
Ponding Water Basics
Asphalt Roofing Manufacturers Association (ARMA)
Ponding water defined as water remaining on a roof 48 hours or longer, a minimum quarter-inch-per-foot slope for free drainage, and the consequences of ponding: deck deformation under load, ice movement, algae and vegetation growth, contamination, accelerated deterioration, and moisture intrusion.
A trade association representing manufacturers of one material family. Used here for a definition and a drainage benchmark, not for product comparison.
Virginia Uniform Statewide Building Code (USBC)
Virginia Department of Housing and Community Development
The statewide-code model as an example: a code based on nationally accepted model codes with state amendments, where enforcement is the responsibility of each local government’s building inspections department.
One state’s arrangement, cited to illustrate the adoption-and-amendment model. It says nothing about requirements in any other jurisdiction, and the current edition and effective date must be checked at the source.
R905.2.6.1 Classification of asphalt shingles (2020 Florida Building Code — Residential, 7th edition, as republished)
UpCodes
That adopted code text classifies asphalt shingles under ASTM D3161, TAS 107, or ASTM D7158, and maps classes to design wind speeds — D3161 Class D or D7158 Class G where Vasd is 100 mph or less, and D3161 Class F, TAS 107, or D7158 Class H for all wind speeds.
A commercial republisher, not the official code source, and one state at one edition. Cited only to show the shape of the class-to-wind-speed mapping. It is not the law in any other jurisdiction and must be verified against the officially adopted edition.
Roof recover restrictions (Texas Windstorm Insurance Association Building Code 2024, Section 1512.3, as republished)
UpCodes
The shape of adopted roof-recover restrictions: recover prohibited where the existing roof already has two or more applications of any covering, where the existing roof or covering is water-soaked or too deteriorated to serve as a base, and where the existing covering is slate, clay, cement, or asbestos-cement tile.
A commercial republisher of one adopted code at one edition. Layer limits and exceptions differ by jurisdiction; confirm with the authority having jurisdiction.

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