For homeowners, buyers, and anyone reading a roofing proposal

Most of what a roof does happens under the layer you can see.

Steep-slope residential · structure-to-covering assembly

This is the reference page. Every other guide on this site links here instead of re-explaining what a deck, an underlayment, or a flashing is.

30-second answer

What are the layers of a roof called, and what does each one actually do?

A roof is a stack of layers, each with one job. Structure carries the load. Deck spans the framing and gives everything a nailing surface. Underlayment is the backup drainage plane. Flashing seals every interruption. The covering sheds most of the water and takes the weather. Drainage moves it off the building. Air, thermal, and vapor control layers sit underneath.

Stop — immediate hazard

Do not climb up to identify any of this.

Nothing on this page requires roof access. Falls are the dominant hazard in roofing work: OSHA requires workers in residential construction six feet or more above a lower level to be protected by guardrails, safety nets, or a personal fall-arrest system. A homeowner on a ladder has none of those.

Attic entry is its own hazard — unguarded ceiling joists, low clearance, extreme summer heat, loose insulation, and, in older buildings, materials that may contain asbestos. The overhead electrical service drop usually lands at the eave, which is exactly where a ladder wants to go.

Everything below is written to be checked from the ground, from a window, from your documents, or by someone whose job it is.

If you can see a dip or a wave in the roof plane, water anywhere near a light fixture or an electrical panel, or a power line touching the roof, the gutter, or a tree above them — keep everyone out and away from that part of the building and call 911 or your utility’s emergency line before anyone goes near it.

Learning paths and saved lessons

At a glance

The short versionSection link

Four things worth carrying into a conversation with an installer.

Named parts in this page’s section drawing: 13Structure, deck, underlayment, eave ice barrier, covering, edge metal, gutter, intake vent, vent channel, insulation, ceiling air barrier, ridge exhaust, and the flashing at a penetration.
Roughly how many you can see from the street: 4The covering, the edge metal, the gutters, and some flashing. Everything else is inferred from documents, from symptoms inside, or seen only during tear-off.
What the covering actually is: A water-shedding surfaceNot a waterproof membrane. NRCA writes its steep-slope application recommendations for substrates at 4:12 (18 degrees) or steeper, where rapid and complete drainage is what keeps water out.
Where roofs leak: At the interruptionsDOE’s Building America Solution Center calls valleys and penetrations through the roof decking “among the most vulnerable areas for water intrusion.”

Scope

Where this model of a roof holds, and where it does notSection link

This page draws one assembly in detail. Saying which one, out loud, is the difference between a reference and a generalization.

Best when

The roof is steep-slope and residential: shingles, metal, tile, wood, or slate over a wood deck carried by rafters or trusses.
There is an attic or a rafter cavity between the roof plane and the ceiling below it.
You are trying to read a proposal, a home-inspection report, or an insurance scope and need to know what the nouns in it refer to.
You want to understand why two quotes for “a new roof” can describe genuinely different amounts of work.

Think twice if

The roof is low-slope or flat. Those assemblies use a waterproof membrane rather than overlapping units that shed water, and the layer order, the drainage strategy, and the failure modes are all different.
The covering is tile or slate on battens or on spaced sheathing. There the underlayment does far more of the waterproofing work than this drawing suggests, and the deck may not be continuous at all.
The assembly is an unvented cathedral ceiling, a structural insulated panel, or a nailbase panel roof. The insulation and air control layers move above or into the roof deck, and callouts 8 to 11 in the diagram simply do not exist in that form.
The deck is steel or concrete, or the covering is metal on purlins with no continuous deck beneath it. Both are common on outbuildings and light commercial buildings.
The building is historic and the roof is part of what is protected. Preservation requirements can outrank the assembly this page treats as the default.

What changes the answer

Slope. It decides whether a water-shedding covering is appropriate at all, and every material has a manufacturer-stated minimum slope.
The adopted code edition and its local amendments. Ice-barrier extent, underlayment, layer limits, ventilation, and edge metal are all set by the jurisdiction, not nationally.
Climate zone and the hazards that come with it — snow load, ice damming, wind-driven rain, wildfire ember exposure, hail frequency.
Whether the attic is vented or unvented. Both are legitimate approaches, and they place the insulation and air-control layers in different planes.
Existing conditions. A 1950s roof deck, a previous overlay, or a chimney that was never properly flashed changes what can be built on top of it.

The section

Cut the roof open at the eave and walk up to the ridgeSection link

Every layer below sits on the one under it and is defeated by a failure in the one above it. That dependency is the whole reason a roof is discussed as a system.

Section through a steep-slope roof assembly at a 6:12 pitch, cut from the eave and gutter on the left to the ridge on the right, with a plumbing vent penetration in the middle of the slope. The far slope is drawn with the same four bands so the ridge reads as a ridge. Numbers 1–13 are named in the table directly below; nothing in the drawing depends on color to be understood.Original diagram, Understanding Roofing. Schematic — not a construction detail.

Key to the section drawing above: every numbered callout, what it is for, how it fails, and what a reader can check without going up a ladder.
Callout	What it does	What goes wrong when it is missing, undersized, or damaged	What you can check from the ground
1 · Roof structure	Rafters or trusses. Carries the roof’s own weight plus snow, wind uplift, and anything else the roof is asked to hold, and delivers it into the walls. Everything above it is cargo.	Deflection. A plane that dips, a ridge that sags in the middle, a bay that bows. Changing from asphalt to tile or slate multiplies the permanent load and is an engineering question, not a shopping decision.	Sight along the ridge and along the eave line from across the street. A sound roof plane looks straight. A dip, a wave, or a bowed ridge is visible from the sidewalk in flat light.
2 · Roof deck (sheathing)	The continuous surface spanning the framing. Gives every fastener something to bite, ties the roof planes together, and carries wind uplift into the structure. DOE’s Building America Solution Center, citing IBHS, recommends a minimum 7/16 in. plywood or OSB deck fastened with 8d ring-shank nails at 4 in. on center within 4 ft of edges and ridge and 6 in. elsewhere — a recommendation, not a code determination.	Wet, rotted, or delaminated sheathing does not hold a nail. Shingles fastened into soft deck lift in wind. Deck condition is generally not knowable until the covering comes off, which is why deck replacement belongs in a contract as a unit price or an allowance rather than a fixed line.	You cannot see the deck. You can see its shape: sagging between rafters reads as a rippled or quilted surface in low, raking sunlight — the reason a late-afternoon photo of the roof is worth taking.
3 · Underlayment	The second drainage plane, over the deck and under the covering. Water that gets past the covering — wind-driven rain, a lifted tab, meltwater — is meant to run down the underlayment to the eave rather than into the deck.	Skipped, torn during installation, or left exposed to weather for weeks before the covering goes on. It is a backup, not a roof, and it is not intended to be the finished surface.	Not visible once the roof is complete. It is visible in progress photographs, named by product in a written proposal, and listed on the material delivery ticket. Ask for all three.
4 · Ice barrier at the eave	A self-adhering membrane over the deck at the eave that seals around fasteners, so water standing behind an ice dam has nowhere to enter. The Building America Solution Center, citing the 2018 IRC, describes an ice barrier extending from the lowest edge of the roof to a point not less than 24 inches inside the interior plane of the exterior wall — the dashed line in the drawing.	Absent, or stopped short of that line, in a place where ice dams form. The dam then backs meltwater up under the covering and into the wall top plate and the ceiling below.	Not visible. Its absence announces itself in winter: icicles along the eave, ice filling the gutter, and a stain appearing on the ceiling at the top of an exterior wall during a thaw.
5 · Roof covering	Takes the weather, resists sunlight and impact, and sheds the water. On a steep slope it is a water-shedding surface made of overlapping units — not a waterproof membrane. NRCA writes its steep-slope recommendations for substrates at 4:12 or steeper, where rapid and complete drainage is what keeps water out.	Missing, creased, or curled units break the overlap pattern. So does a fastener in the wrong place: every nail driven above the intended zone, or overdriven through the mat, is a hole in the drainage plane held shut by nothing.	This is the layer you can genuinely inspect from the ground. Missing units, dark patches where granules have gone, lifted edges after a windstorm, and repairs that do not match the surrounding field.
6 · Drip edge (edge metal)	Metal at the eaves and rakes that carries water off the deck edge into the gutter instead of behind it, and stiffens the most wind-loaded part of the roof. Building America notes roof edges see the highest positive and negative pressures in a windstorm, and that most covering blow-off starts there.	Without it, water wicks back onto the fascia and behind the gutter. Fascia and soffit rot first, then the deck edge, and the repair is no longer a roofing repair.	Look along the eave and up the rake: a thin metal lip should be visible under the first course. Soft or stained fascia beneath an otherwise sound roof is the classic sign it is missing or was installed under the underlayment instead of over the deck edge.
7 · Gutters and downspouts	Collect what the roof sheds and move it away from the building. Building America notes a few inches of rain on a house roof can produce several thousand gallons of runoff, and recommends gutters sloped at least 1/16 in. per foot of run, downspouts every 20 to 50 feet, and discharge at least 5 feet from the foundation or into a catchment at least 10 feet away.	Undersized, flat, or blocked gutters overflow at the back edge rather than the front, which soaks the fascia and the wall below. Downspouts that discharge at the foundation move a roof problem into the basement.	Watch them in a real rainstorm from a window. Water sheeting over the front edge, water running behind the gutter, and a saturated strip of soil directly under a downspout are all visible from inside.
8 · Intake ventilation	In a vented assembly, the soffit or eave openings where outside air enters. Intake is the half of ventilation that gets forgotten, because exhaust is the half you can see from the street.	Blocked by insulation pushed into the eave, painted shut, or never installed while ridge vent was. Exhaust with no intake pulls its make-up air from the house through ceiling leaks, which is the opposite of the intent.	Stand under the eave and look up: soffit vents should be open, not filled with paint or debris. This one is genuinely checkable from the ground.
9 · Ventilation channel	The clear path from the intake at the eave to the exhaust at the ridge, held open above the insulation by baffles. Building America’s ice-dam guidance calls for maintaining a 2-inch vent space.	Insulation stuffed into the eave closes the channel at exactly the point where it matters most, so the eave runs cold while the upper deck stays warm — the temperature difference an ice dam needs.	Not visible. It is a normal finding in a professional attic inspection or an energy audit, and it is worth asking about specifically rather than accepting “ventilation is fine.”
10 · Insulation	Slows heat flow between the conditioned space and the roof or attic. In a vented attic it lies on the ceiling; in an unvented assembly it moves up to the roof deck plane. For unconditioned, ventilated attics specifically, Building America’s ice-dam guidance recommends R-60 or greater in climate zones 5 and above — a figure for that assembly, not a number to carry across to an unvented roof, where the controlling requirement is a minimum air-impermeable insulation R-value by climate zone.	Thin, compressed, gapped at the eaves, or missing over dropped ceilings and soffits. Heat escaping through those gaps warms the deck, melts snow, and refreezes at the cold eave.	Not visible, but its effects are. Snow melting off one part of a roof while it lies undisturbed on the rest, in a pattern that repeats every winter, is a heat-loss map drawn on your own house.
11 · Ceiling air barrier	The continuous layer that stops indoor air leaking into the attic — sealed drywall, sealed penetrations, sealed top plates, a sealed attic hatch. Building America is unambiguous that heat loss through air leakage warming the roof deck is one of the greatest sources of ice dams in residential construction, and that sealing those leaks is the most important step.	Recessed lights, plumbing chases, bath fans, and the attic hatch leaking warm, moist indoor air upward. That air both warms the deck and condenses on it, which is why the same defect produces both ice dams and attic mold.	Not visible, but inferable: a drafty attic hatch, a bathroom fan that vents into the attic rather than outdoors, and frost on nail points visible in a winter inspection photograph.
12 · Ridge and exhaust ventilation	The ridge is the peak where two planes meet. In a vented assembly it is usually also the exhaust: a slot cut in the deck, covered by a vent and the ridge cap.	Mixing exhaust types — ridge vent plus gable vents plus powered fans — can let one short-circuit another so air enters at the nearest opening instead of at the eaves. A ridge vent with no slot cut beneath it is decoration.	The ridge cap is visible from the ground. So are gable vents and roof-mounted fans, which is enough to ask whether the roof has more than one exhaust type competing.
13 · Penetration and boot flashing	Any pipe, fan, or conduit through the roof plane is a hole in the drainage plane. Its flashing is a flange laid into the shingle courses plus a collar sealing to the pipe. Building America calls penetrations through the roof decking among the most vulnerable areas for water intrusion.	The flange installed on top of the courses instead of woven into them, so water runs under it. Or the rubber collar cracks with age and sunlight while the roof around it is still sound.	Count the penetrations from the ground and photograph them with a zoom lens. Cracked or lifted collars are often visible in a phone photo taken from a window across the way.

Read this table one item at a time

1 · Roof structure

What it does: Rafters or trusses. Carries the roof’s own weight plus snow, wind uplift, and anything else the roof is asked to hold, and delivers it into the walls. Everything above it is cargo.
What goes wrong when it is missing, undersized, or damaged: Deflection. A plane that dips, a ridge that sags in the middle, a bay that bows. Changing from asphalt to tile or slate multiplies the permanent load and is an engineering question, not a shopping decision.
What you can check from the ground: Sight along the ridge and along the eave line from across the street. A sound roof plane looks straight. A dip, a wave, or a bowed ridge is visible from the sidewalk in flat light.

2 · Roof deck (sheathing)

What it does: The continuous surface spanning the framing. Gives every fastener something to bite, ties the roof planes together, and carries wind uplift into the structure. DOE’s Building America Solution Center, citing IBHS, recommends a minimum 7/16 in. plywood or OSB deck fastened with 8d ring-shank nails at 4 in. on center within 4 ft of edges and ridge and 6 in. elsewhere — a recommendation, not a code determination.
What goes wrong when it is missing, undersized, or damaged: Wet, rotted, or delaminated sheathing does not hold a nail. Shingles fastened into soft deck lift in wind. Deck condition is generally not knowable until the covering comes off, which is why deck replacement belongs in a contract as a unit price or an allowance rather than a fixed line.
What you can check from the ground: You cannot see the deck. You can see its shape: sagging between rafters reads as a rippled or quilted surface in low, raking sunlight — the reason a late-afternoon photo of the roof is worth taking.

3 · Underlayment

What it does: The second drainage plane, over the deck and under the covering. Water that gets past the covering — wind-driven rain, a lifted tab, meltwater — is meant to run down the underlayment to the eave rather than into the deck.
What goes wrong when it is missing, undersized, or damaged: Skipped, torn during installation, or left exposed to weather for weeks before the covering goes on. It is a backup, not a roof, and it is not intended to be the finished surface.
What you can check from the ground: Not visible once the roof is complete. It is visible in progress photographs, named by product in a written proposal, and listed on the material delivery ticket. Ask for all three.

4 · Ice barrier at the eave

What it does: A self-adhering membrane over the deck at the eave that seals around fasteners, so water standing behind an ice dam has nowhere to enter. The Building America Solution Center, citing the 2018 IRC, describes an ice barrier extending from the lowest edge of the roof to a point not less than 24 inches inside the interior plane of the exterior wall — the dashed line in the drawing.
What goes wrong when it is missing, undersized, or damaged: Absent, or stopped short of that line, in a place where ice dams form. The dam then backs meltwater up under the covering and into the wall top plate and the ceiling below.
What you can check from the ground: Not visible. Its absence announces itself in winter: icicles along the eave, ice filling the gutter, and a stain appearing on the ceiling at the top of an exterior wall during a thaw.

5 · Roof covering

What it does: Takes the weather, resists sunlight and impact, and sheds the water. On a steep slope it is a water-shedding surface made of overlapping units — not a waterproof membrane. NRCA writes its steep-slope recommendations for substrates at 4:12 or steeper, where rapid and complete drainage is what keeps water out.
What goes wrong when it is missing, undersized, or damaged: Missing, creased, or curled units break the overlap pattern. So does a fastener in the wrong place: every nail driven above the intended zone, or overdriven through the mat, is a hole in the drainage plane held shut by nothing.
What you can check from the ground: This is the layer you can genuinely inspect from the ground. Missing units, dark patches where granules have gone, lifted edges after a windstorm, and repairs that do not match the surrounding field.

6 · Drip edge (edge metal)

What it does: Metal at the eaves and rakes that carries water off the deck edge into the gutter instead of behind it, and stiffens the most wind-loaded part of the roof. Building America notes roof edges see the highest positive and negative pressures in a windstorm, and that most covering blow-off starts there.
What goes wrong when it is missing, undersized, or damaged: Without it, water wicks back onto the fascia and behind the gutter. Fascia and soffit rot first, then the deck edge, and the repair is no longer a roofing repair.
What you can check from the ground: Look along the eave and up the rake: a thin metal lip should be visible under the first course. Soft or stained fascia beneath an otherwise sound roof is the classic sign it is missing or was installed under the underlayment instead of over the deck edge.

7 · Gutters and downspouts

What it does: Collect what the roof sheds and move it away from the building. Building America notes a few inches of rain on a house roof can produce several thousand gallons of runoff, and recommends gutters sloped at least 1/16 in. per foot of run, downspouts every 20 to 50 feet, and discharge at least 5 feet from the foundation or into a catchment at least 10 feet away.
What goes wrong when it is missing, undersized, or damaged: Undersized, flat, or blocked gutters overflow at the back edge rather than the front, which soaks the fascia and the wall below. Downspouts that discharge at the foundation move a roof problem into the basement.
What you can check from the ground: Watch them in a real rainstorm from a window. Water sheeting over the front edge, water running behind the gutter, and a saturated strip of soil directly under a downspout are all visible from inside.

8 · Intake ventilation

What it does: In a vented assembly, the soffit or eave openings where outside air enters. Intake is the half of ventilation that gets forgotten, because exhaust is the half you can see from the street.
What goes wrong when it is missing, undersized, or damaged: Blocked by insulation pushed into the eave, painted shut, or never installed while ridge vent was. Exhaust with no intake pulls its make-up air from the house through ceiling leaks, which is the opposite of the intent.
What you can check from the ground: Stand under the eave and look up: soffit vents should be open, not filled with paint or debris. This one is genuinely checkable from the ground.

9 · Ventilation channel

What it does: The clear path from the intake at the eave to the exhaust at the ridge, held open above the insulation by baffles. Building America’s ice-dam guidance calls for maintaining a 2-inch vent space.
What goes wrong when it is missing, undersized, or damaged: Insulation stuffed into the eave closes the channel at exactly the point where it matters most, so the eave runs cold while the upper deck stays warm — the temperature difference an ice dam needs.
What you can check from the ground: Not visible. It is a normal finding in a professional attic inspection or an energy audit, and it is worth asking about specifically rather than accepting “ventilation is fine.”

10 · Insulation

What it does: Slows heat flow between the conditioned space and the roof or attic. In a vented attic it lies on the ceiling; in an unvented assembly it moves up to the roof deck plane. For unconditioned, ventilated attics specifically, Building America’s ice-dam guidance recommends R-60 or greater in climate zones 5 and above — a figure for that assembly, not a number to carry across to an unvented roof, where the controlling requirement is a minimum air-impermeable insulation R-value by climate zone.
What goes wrong when it is missing, undersized, or damaged: Thin, compressed, gapped at the eaves, or missing over dropped ceilings and soffits. Heat escaping through those gaps warms the deck, melts snow, and refreezes at the cold eave.
What you can check from the ground: Not visible, but its effects are. Snow melting off one part of a roof while it lies undisturbed on the rest, in a pattern that repeats every winter, is a heat-loss map drawn on your own house.

11 · Ceiling air barrier

What it does: The continuous layer that stops indoor air leaking into the attic — sealed drywall, sealed penetrations, sealed top plates, a sealed attic hatch. Building America is unambiguous that heat loss through air leakage warming the roof deck is one of the greatest sources of ice dams in residential construction, and that sealing those leaks is the most important step.
What goes wrong when it is missing, undersized, or damaged: Recessed lights, plumbing chases, bath fans, and the attic hatch leaking warm, moist indoor air upward. That air both warms the deck and condenses on it, which is why the same defect produces both ice dams and attic mold.
What you can check from the ground: Not visible, but inferable: a drafty attic hatch, a bathroom fan that vents into the attic rather than outdoors, and frost on nail points visible in a winter inspection photograph.

12 · Ridge and exhaust ventilation

What it does: The ridge is the peak where two planes meet. In a vented assembly it is usually also the exhaust: a slot cut in the deck, covered by a vent and the ridge cap.
What goes wrong when it is missing, undersized, or damaged: Mixing exhaust types — ridge vent plus gable vents plus powered fans — can let one short-circuit another so air enters at the nearest opening instead of at the eaves. A ridge vent with no slot cut beneath it is decoration.
What you can check from the ground: The ridge cap is visible from the ground. So are gable vents and roof-mounted fans, which is enough to ask whether the roof has more than one exhaust type competing.

13 · Penetration and boot flashing

What it does: Any pipe, fan, or conduit through the roof plane is a hole in the drainage plane. Its flashing is a flange laid into the shingle courses plus a collar sealing to the pipe. Building America calls penetrations through the roof decking among the most vulnerable areas for water intrusion.
What goes wrong when it is missing, undersized, or damaged: The flange installed on top of the courses instead of woven into them, so water runs under it. Or the rubber collar cracks with age and sunlight while the roof around it is still sound.
What you can check from the ground: Count the penetrations from the ground and photograph them with a zoom lens. Cracked or lifted collars are often visible in a phone photo taken from a window across the way.

This table is the text equivalent of the drawing. It is complete on its own: a reader who never sees the image loses nothing. Each layer also has a short dictionary entry — structure, roof deck, underlayment, ice barrier, covering, drip edge, gutter, intake vent, baffle, air barrier, ridge vent, and pipe boot.

The order is the argument

A roof works because water crosses each layer in one direction only. The covering sheds most of it. What gets through lands on the underlayment and runs to the eave. What reaches the deck has already defeated two layers, and the deck has no third one behind it. This is why a repair that fixes a symptom above the leak but leaves the layer below it wet does not fix anything: the water is already inside the assembly, and the assembly has no way to dry to the outside.

It is also why the sequence matters at installation. Underlayment laid over the drip edge at the rake, flashing set on top of the courses rather than woven into them, or a sealant bead standing in for a piece of metal all reverse the direction of the lap. The materials are all present, the invoice looks complete, and the roof leaks anyway.

The covering sheds; it does not seal

This is the single most useful correction most readers can make to their mental model. A shingle, tile, shake, or metal panel roof is a set of overlapping units arranged so gravity carries water from one course to the next. NRCA writes its steep-slope application recommendations for substrates at 4:12 or steeper because rapid and complete drainage is what makes that arrangement work. Reduce the slope, interrupt the pattern, or hold water against the surface with debris or an ice dam, and water starts moving sideways and upward under the units instead of down over them.

Low-slope roofs solve the same problem differently: a continuous waterproof membrane with sealed seams, designed to hold water rather than shed it. Neither approach is better; they are answers to different geometry. Using one where the other belongs is a category error that no quality of workmanship rescues.

Where the layers get interrupted

The middle of an uninterrupted roof plane is the most robust part of the whole assembly. Most of what leaks is a place where the plane stops, turns, or is punctured — and the detail that handles that interruption is usually a piece of metal called flashing. The plan below names those places on a fairly ordinary house.

Plan view of a hipped main roof with a gabled wing and a two-story wall along one side, at equal pitch. Arrows show which way each plane drains. Ridges and hips are drawn as heavy dark lines; the interruptions that concentrate water — the two valleys and the roof-to-wall run — are drawn heavier still and named by the letters A–J in the table below.Original diagram, Understanding Roofing. Schematic — not a construction detail.

Key to the plan drawing above: each named location on a roof, why the geometry creates it, how it is detailed, and what its failure looks like.
Callout	Why the roof has one	How it is detailed	What failure looks like
A · Ridge	The horizontal line where two roof planes meet at the top. Water runs away from it in both directions.	Ridge cap units over the joint, often over a slot cut in the deck for exhaust ventilation.	Lifted or missing cap units after wind; a sagging ridge line, which is a structural sign rather than a covering one.
B · Hip	The sloped line where two planes meet on an outside corner. Like a ridge, it sheds water away from itself in both directions.	Cap units run up the line over the field courses, with the cut edges of both planes woven or trimmed beneath them.	Cap units sliding or lifting; exposed cut edges where the caps have gone, which lets water into the joint.
C · Valley	The sloped line where two planes meet on an inside corner. Every drop landing on either plane above it ends up here, so a valley carries far more water per foot than the field does.	Open metal valley, or a woven or closed-cut shingle valley, usually over a self-adhering membrane. Building America recommends sealing valleys with membrane laid directly on the sheathing, lapped 6 inches in shingle fashion from the low point upward.	Wear stripes down the center where the flow is fastest; debris packed at the bottom holding water; a ceiling stain that appears only in heavy rain, when the valley is running full.
D · Eave	The low edge of a plane, where water leaves the roof. Everything the plane collects arrives here.	Drip edge over the deck, underlayment or ice barrier lapped to the correct side of it, gutter hung below, first course overhanging slightly so water clears the edge.	Rotted fascia and soffit; ice build-up in winter; water dripping behind the gutter rather than into it.
E · Rake	The sloped edge of a gable end. Water runs across it rather than off it, and wind gets under it.	Rake drip edge over the underlayment, with the covering overhanging enough to shed clear of the trim.	Lifted units along the edge after a windstorm; stained or peeling rake trim; a gap where the metal has pulled away.
F · Roof-to-wall junction	Wherever a roof plane runs into a wall that continues past it — a taller section, a dormer cheek, a chimney side.	Step flashing: individual L-shaped pieces, one per course, woven into the courses and lapped up the wall behind the cladding. Building America, citing the 2015 IRC, describes step flashing extending at least 4 inches up the wall and 4 inches out onto the roof deck, in galvanized steel at least 0.019 inches thick where metal is used.	A continuous strip of metal or a bead of sealant where individual steps belong. Blistered paint, staining, or soft cladding along the junction. Water appearing inside the wall rather than the ceiling.
G · Kickout flashing	The specific point where a roof edge dies into a wall — the bottom end of a step-flashed run. Without a diverter, the water arriving there runs straight down the wall behind the cladding.	A single flared piece at the bottom of the step flashing run that kicks water out into the gutter. Building America says missing kickout flashing “has been responsible for thousands of dollars worth of damage for homeowners,” and that an undersized diverter is ineffective.	A vertical stain or a stripe of failed paint on the wall below the junction; soft sheathing behind it; a persistent damp patch inside that has nothing to do with the roof plane itself.
H · Chimney and cricket	A wide penetration sitting in the flow. Water arriving from the slope above has to get around it, and snow and debris pile up on the upslope side.	Step flashing up the sides, counter flashing let into the masonry above it, apron at the front, and on wider chimneys a cricket — a small saddle roof that splits the flow and sends it around each side.	Tar smeared over a joint that should hold a metal counter flashing; rust stains; a rotted deck patch on the upslope side; interior staining that appears at the chimney chase.
I · Plumbing vent penetration	Every drainage system needs vents through the roof, and bath fans and range hoods often exhaust through it as well.	A boot or collar flashing with its flange woven into the courses. Building America describes sealing the deck around penetrations with membrane at least 6 inches on each side and below before the flashing goes on.	A cracked or slumped rubber collar; sealant applied over the top of the flange as a repair; a ceiling stain a room or two away from the pipe, because water travels along framing before it drips.
J · Skylight	A large penetration with a head, a sill, and two sides, each needing a different detail.	A manufacturer’s flashing kit for that unit at that pitch: sill flashing, step flashing up both sides, head flashing lapped under the courses above, typically over membrane on the deck.	Condensation mistaken for a leak; staining at the head, which means the upper lap is reversed; a kit substituted with sealant, which is a maintenance material standing in for a permanent detail.

Read this table one item at a time

A · Ridge

Why the roof has one: The horizontal line where two roof planes meet at the top. Water runs away from it in both directions.
How it is detailed: Ridge cap units over the joint, often over a slot cut in the deck for exhaust ventilation.
What failure looks like: Lifted or missing cap units after wind; a sagging ridge line, which is a structural sign rather than a covering one.

B · Hip

Why the roof has one: The sloped line where two planes meet on an outside corner. Like a ridge, it sheds water away from itself in both directions.
How it is detailed: Cap units run up the line over the field courses, with the cut edges of both planes woven or trimmed beneath them.
What failure looks like: Cap units sliding or lifting; exposed cut edges where the caps have gone, which lets water into the joint.

C · Valley

Why the roof has one: The sloped line where two planes meet on an inside corner. Every drop landing on either plane above it ends up here, so a valley carries far more water per foot than the field does.
How it is detailed: Open metal valley, or a woven or closed-cut shingle valley, usually over a self-adhering membrane. Building America recommends sealing valleys with membrane laid directly on the sheathing, lapped 6 inches in shingle fashion from the low point upward.
What failure looks like: Wear stripes down the center where the flow is fastest; debris packed at the bottom holding water; a ceiling stain that appears only in heavy rain, when the valley is running full.

D · Eave

Why the roof has one: The low edge of a plane, where water leaves the roof. Everything the plane collects arrives here.
How it is detailed: Drip edge over the deck, underlayment or ice barrier lapped to the correct side of it, gutter hung below, first course overhanging slightly so water clears the edge.
What failure looks like: Rotted fascia and soffit; ice build-up in winter; water dripping behind the gutter rather than into it.

E · Rake

Why the roof has one: The sloped edge of a gable end. Water runs across it rather than off it, and wind gets under it.
How it is detailed: Rake drip edge over the underlayment, with the covering overhanging enough to shed clear of the trim.
What failure looks like: Lifted units along the edge after a windstorm; stained or peeling rake trim; a gap where the metal has pulled away.

F · Roof-to-wall junction

Why the roof has one: Wherever a roof plane runs into a wall that continues past it — a taller section, a dormer cheek, a chimney side.
How it is detailed: Step flashing: individual L-shaped pieces, one per course, woven into the courses and lapped up the wall behind the cladding. Building America, citing the 2015 IRC, describes step flashing extending at least 4 inches up the wall and 4 inches out onto the roof deck, in galvanized steel at least 0.019 inches thick where metal is used.
What failure looks like: A continuous strip of metal or a bead of sealant where individual steps belong. Blistered paint, staining, or soft cladding along the junction. Water appearing inside the wall rather than the ceiling.

G · Kickout flashing

Why the roof has one: The specific point where a roof edge dies into a wall — the bottom end of a step-flashed run. Without a diverter, the water arriving there runs straight down the wall behind the cladding.
How it is detailed: A single flared piece at the bottom of the step flashing run that kicks water out into the gutter. Building America says missing kickout flashing “has been responsible for thousands of dollars worth of damage for homeowners,” and that an undersized diverter is ineffective.
What failure looks like: A vertical stain or a stripe of failed paint on the wall below the junction; soft sheathing behind it; a persistent damp patch inside that has nothing to do with the roof plane itself.

H · Chimney and cricket

Why the roof has one: A wide penetration sitting in the flow. Water arriving from the slope above has to get around it, and snow and debris pile up on the upslope side.
How it is detailed: Step flashing up the sides, counter flashing let into the masonry above it, apron at the front, and on wider chimneys a cricket — a small saddle roof that splits the flow and sends it around each side.
What failure looks like: Tar smeared over a joint that should hold a metal counter flashing; rust stains; a rotted deck patch on the upslope side; interior staining that appears at the chimney chase.

I · Plumbing vent penetration

Why the roof has one: Every drainage system needs vents through the roof, and bath fans and range hoods often exhaust through it as well.
How it is detailed: A boot or collar flashing with its flange woven into the courses. Building America describes sealing the deck around penetrations with membrane at least 6 inches on each side and below before the flashing goes on.
What failure looks like: A cracked or slumped rubber collar; sealant applied over the top of the flange as a repair; a ceiling stain a room or two away from the pipe, because water travels along framing before it drips.

J · Skylight

Why the roof has one: A large penetration with a head, a sill, and two sides, each needing a different detail.
How it is detailed: A manufacturer’s flashing kit for that unit at that pitch: sill flashing, step flashing up both sides, head flashing lapped under the courses above, typically over membrane on the deck.
What failure looks like: Condensation mistaken for a leak; staining at the head, which means the upper lap is reversed; a kit substituted with sealant, which is a maintenance material standing in for a permanent detail.

Hips and ridges shed water away from the line. Valleys and roof-to-wall junctions collect it and concentrate it. That is the whole reason the second group is where roofs leak. Dictionary entries: ridge, hip, valley, eave, rake, step flashing, kickout flashing, and cricket.

Without a ladder

What you can actually establish from each vantage pointSection link

The honest answer to “how do I check my roof” is that a homeowner can establish more than they expect and less than they hope. Knowing which is which is what keeps people off ladders.

Every row below is a real method. None of them requires roof access, and the last two are things you commission rather than perform. The column that matters most is the third one: knowing what a method cannot tell you is what stops a reassuring look from the driveway becoming a decision.

This table is deliberately shallow — it is here to say which of the thirteen layers each vantage point can reach, not to teach a method. Two sibling pages carry the depth: roof measurement covers the ground-based, satellite, and plan-based techniques and the accuracy each one actually achieves, and roof inspection covers what the different kinds of professional inspection do and do not include.

What each vantage point can and cannot establish about the thirteen layers, and who should be doing it.
Where you look	What it can establish	What it cannot	Who does it
From the ground, with binoculars or a zoom lens	Missing, lifted, curled, or mismatched covering units. Granule loss as dark patches. Whether drip edge is present at the eave and rake. Gutter alignment and condition. Sagging or waves in the roof plane. The number and condition of penetrations. Sealant used as a repair.	Anything under the covering: deck condition, underlayment, ice barrier, fastener placement, or whether flashing is woven into the courses or laid on top of them.	You. This is the safest and most informative thing a homeowner can do, and a phone photo at maximum zoom in late-afternoon light is often better than a glance.
From an upstairs window or a neighboring building	The condition of a plane you cannot see from the street — often the back slope, where nobody has looked in twenty years. Valley debris. Vent collars. Ridge cap condition.	Anything on a plane with no facing window, and any detail behind a parapet or dormer cheek.	You, from inside. Never from a ladder set on soft ground, a deck rail, or in reach of the service drop.
From documents	The age of the covering, the products used, the scope of the last job, the permit record and inspection history, and whether flashing and deck work were included last time. Warranty registrations name the product and the installer.	The current condition of anything. A document establishes what was intended and paid for, not what is there now.	You, plus your local building department for permit records. This is the most underused source of roof information there is.
From inside the house, without entering the attic	Ceiling and wall staining and its pattern; whether it appears in heavy rain, in wind-driven rain, or during a thaw; drafts at the attic hatch; bathroom fans that sound like they vent into the attic rather than outdoors.	Where water entered. The stain marks the exit, not the entry, and correlating the two takes access above the ceiling.	You. Recording the date, the weather, and a photograph each time the stain changes is worth more to a diagnostician than the stain itself.
From aerial or satellite imagery	Roof geometry: how many planes, valleys, hips, and penetrations exist, and roughly how complex the roof is. Useful for sanity-checking a measurement in a proposal.	Condition, age, or layer count. Imagery is often years old, and image quality varies enormously between providers and dates.	You, free, in a few minutes — with the caveat that a takeoff from imagery is an estimate, not a measurement.
From the attic	Deck staining, daylight at penetrations, frost on fastener points, compressed or missing insulation, blocked eave channels, and disconnected exhaust ducts.	Anything above the deck, and anything hidden by insulation. It also cannot be done safely by an untrained person.	A home inspector, an energy auditor, or a roofing contractor. Unguarded joists, low clearance, extreme heat, and possible asbestos-containing material make this a professional task, not a weekend one.
During tear-off	The only complete answer. Deck condition sheet by sheet, previous layers, old flashing, and what was actually under the last roof.	Nothing — but it arrives too late to inform the decision to do the work, which is exactly why deck allowances and unit prices belong in the contract beforehand.	The crew doing the work. Ask to be shown, or ask for dated photographs of anything replaced.

Read this table one item at a time

From the ground, with binoculars or a zoom lens

What it can establish: Missing, lifted, curled, or mismatched covering units. Granule loss as dark patches. Whether drip edge is present at the eave and rake. Gutter alignment and condition. Sagging or waves in the roof plane. The number and condition of penetrations. Sealant used as a repair.
What it cannot: Anything under the covering: deck condition, underlayment, ice barrier, fastener placement, or whether flashing is woven into the courses or laid on top of them.
Who does it: You. This is the safest and most informative thing a homeowner can do, and a phone photo at maximum zoom in late-afternoon light is often better than a glance.

From an upstairs window or a neighboring building

What it can establish: The condition of a plane you cannot see from the street — often the back slope, where nobody has looked in twenty years. Valley debris. Vent collars. Ridge cap condition.
What it cannot: Anything on a plane with no facing window, and any detail behind a parapet or dormer cheek.
Who does it: You, from inside. Never from a ladder set on soft ground, a deck rail, or in reach of the service drop.

From documents

What it can establish: The age of the covering, the products used, the scope of the last job, the permit record and inspection history, and whether flashing and deck work were included last time. Warranty registrations name the product and the installer.
What it cannot: The current condition of anything. A document establishes what was intended and paid for, not what is there now.
Who does it: You, plus your local building department for permit records. This is the most underused source of roof information there is.

From inside the house, without entering the attic

What it can establish: Ceiling and wall staining and its pattern; whether it appears in heavy rain, in wind-driven rain, or during a thaw; drafts at the attic hatch; bathroom fans that sound like they vent into the attic rather than outdoors.
What it cannot: Where water entered. The stain marks the exit, not the entry, and correlating the two takes access above the ceiling.
Who does it: You. Recording the date, the weather, and a photograph each time the stain changes is worth more to a diagnostician than the stain itself.

From aerial or satellite imagery

What it can establish: Roof geometry: how many planes, valleys, hips, and penetrations exist, and roughly how complex the roof is. Useful for sanity-checking a measurement in a proposal.
What it cannot: Condition, age, or layer count. Imagery is often years old, and image quality varies enormously between providers and dates.
Who does it: You, free, in a few minutes — with the caveat that a takeoff from imagery is an estimate, not a measurement.

From the attic

What it can establish: Deck staining, daylight at penetrations, frost on fastener points, compressed or missing insulation, blocked eave channels, and disconnected exhaust ducts.
What it cannot: Anything above the deck, and anything hidden by insulation. It also cannot be done safely by an untrained person.
Who does it: A home inspector, an energy auditor, or a roofing contractor. Unguarded joists, low clearance, extreme heat, and possible asbestos-containing material make this a professional task, not a weekend one.

During tear-off

What it can establish: The only complete answer. Deck condition sheet by sheet, previous layers, old flashing, and what was actually under the last roof.
What it cannot: Nothing — but it arrives too late to inform the decision to do the work, which is exactly why deck allowances and unit prices belong in the contract beforehand.
Who does it: The crew doing the work. Ask to be shown, or ask for dated photographs of anything replaced.

The layers that are not about water

Five of the thirteen parts are about heat and air, not waterSection link

Callouts 8 to 11, and the vent half of callout 12, look out of place in a drawing about keeping rain out. They are there because the most expensive water problems in cold climates are not rain at all.

Water reaches a roof from two directions. From above it is weather, and the covering, underlayment, and flashings handle it. From below it is indoor air carrying moisture, and no amount of roofing material addresses it. A roof that is perfect at shedding rain can still soak its own deck from the inside every winter.

The mechanism is simple enough to hold in your head. Warm indoor air leaks through ceiling penetrations into the attic. It warms the underside of the deck, so snow lying on the roof melts. The meltwater runs down to the overhang, which is not warmed because there is no heated space beneath it, refreezes, and builds a dam. Water then stands behind that dam, above the eave, and finds its way under the covering. Building America puts this plainly: heat loss into the attic through air leakage that warms the roof deck is one of the greatest sources of ice dams in residential construction, and sealing those air leaks is the most important step.

The same leaking air carries moisture, which condenses on cold sheathing and shows up in spring as attic mold. It is worth saying explicitly: ice dams and attic mold are frequently the same defect, observed in two different places. That is why replacing a roof over an unsealed ceiling reliably produces a new roof with the old problem.

Two legitimate strategies, not one right answer

A vented assembly keeps the deck cold. Outside air enters low at the soffit, travels up a channel held open above the insulation, and exits at the ridge. The insulation lies on the ceiling; the attic is outside the thermal boundary and is meant to be roughly the temperature of the outdoors.

An unvented assembly does the opposite. The insulation and air-control layers move up to the roof-deck plane, the attic becomes part of the conditioned space, and there are no vents at all. Building America describes these as assemblies created by eliminating ventilation openings and moving the thermal, moisture, and air control boundaries to the plane of the roof deck, keeping the deck warm enough that condensation does not occur — which depends on air-impermeable insulation at a minimum R-value set by climate zone.

Both are recognized approaches. Which one is appropriate depends on the climate zone, the assembly, the equipment in the attic, and what the jurisdiction has adopted. What is never appropriate is half of each: a partially insulated roof plane over a partially sealed ceiling, with vents that no longer connect to anything. The intake-and-exhaust arithmetic, and the mistakes that defeat it, are covered on the ventilation page.

Considerations

What changes this on a real buildingSection link

The same thirteen parts appear on nearly every steep-slope roof. What each one has to be is decided locally.

Slope and drainage

Slope is the first gate, before material, budget, or appearance. It decides whether a water-shedding covering is appropriate at all, how much overlap each course needs, and how fast water leaves the plane. Every covering also carries a manufacturer-stated minimum slope, often with a different underlayment requirement below a certain pitch.

Slope is written as rise over run — a 6:12 roof rises 6 inches for every 12 inches of horizontal run, which is the pitch drawn in the section above. It also sets how much roof surface exists above a given footprint, which is why two houses of identical floor area can need very different quantities of material. The arithmetic behind that is on the roof pitch page.

Trade recommendations and adopted code thresholds are not the same document. NRCA writes its steep-slope recommendations for 4:12 and steeper; what a jurisdiction permits, and what a manufacturer requires to honor its own instructions, are separate answers you have to look up for the specific roof.

Moisture and ventilation

Callouts 8 to 11 are not a water-shedding story; they are a heat-and-air story that shows up as a water problem. Warm indoor air leaking into a cold attic does two things at once: it warms the underside of the deck, which melts snow that refreezes at the cold eave, and it carries moisture that condenses on the cold sheathing. Ice dams and attic mold are frequently the same defect observed in two places.

A vented assembly answers this by keeping the deck cold: outside air in at the eave, through a clear channel, out at the ridge. A correctly designed unvented assembly answers it the opposite way, by moving the insulation and air control to the roof-deck plane and keeping the deck warm enough that condensation does not occur. Building America describes both as real strategies, with the unvented approach depending on air-impermeable insulation of a specified minimum R-value for the climate zone.

There is no universal ventilation ratio and no universal answer here. Ventilation requirements depend on the adopted code edition and its amendments, the assembly, the climate zone, and existing conditions. Vented and correctly designed unvented assemblies are both recognized approaches; “more ventilation is always better” is not a true statement about either.

Climate

Where snow sits on a roof long enough to melt and refreeze, the eave detail stops being a trim question. Building America identifies air leakage warming the deck as one of the greatest sources of ice dams, and gives two snow-load markers rather than one: dams are likely anywhere the ground snow load exceeds 30 lb/ft², and typically prevalent above 60 lb/ft². Being under the higher number is not the same as being out of the problem. It puts the sequence in order too: air seal first, insulate second, ventilate third, and treat the eave membrane as protection against the water a dam produces rather than as a fix for the dam itself.

Ice-barrier requirements are jurisdictional, not national. Building America, citing the 2018 IRC as a model provision, describes an ice barrier running from the roof’s lowest edge to at least 24 inches inside the interior plane of the exterior wall. Whether that provision is law where you live, in that edition, with or without amendment, is a question for the authority having jurisdiction.

Wind

Wind does not lift a roof evenly. Pressures are highest at the edges and corners, which is why Building America notes that most covering blow-off starts at roof edges, and why edge metal, the fastening of the first courses, and deck attachment near the perimeter matter more per square foot than anything in the middle of the plane. Once the covering opens at an edge, wind gets under the sheet and peels it, and the underlayment — never intended to be a finished surface — is what stands between the weather and the deck.

Wind performance is a property of a specific building on a specific site: basic wind speed, exposure, building height and geometry, pressure zone, enclosure, risk category, the attachment, and the tested assembly all enter into it. A marketing “mph rating” on a covering is not a code determination for your roof.

Fire

Fire classification is a property of the whole roof assembly as tested — deck, underlayment, and covering together, in the configuration that was tested. Two buildings with the same shingles can carry different classifications if what is under them differs. In wildfire-exposed areas the vulnerable parts are frequently not the covering at all but the openings: eave and ridge vents that admit embers, and gaps at the edges.

A fire class applies to a tested assembly, never to a covering in isolation. If a fire classification matters where you are building, it belongs in the proposal as a named assembly and listing, not as an adjective attached to a product.

Hail and impact

Impact resistance is measured by dropping a defined object on a sample under defined laboratory conditions. That is a genuine, useful comparison between products, and it is not a statement about what a particular storm will do to a particular roof. Hail varies in size, density, shape, terminal velocity, and angle; a covering also gets more brittle as it ages, and the deck under it changes how it responds to a strike.

“Class 4 impact resistant” does not mean hail proof. It means the product performed to a defined level in a defined test, under that test’s conditions. Whether an impact-resistant covering earns anything back on an insurance premium is set by a particular insurer’s filed rates in a particular state, so it is a question for your carrier and your declarations page rather than one this page can answer.

Structural weight

Coverings differ enormously in weight, and the framing under a roof was designed for the load it was built with. Moving from asphalt shingles to clay tile or natural slate is a structural change before it is an aesthetic one, and the answer comes from an engineer looking at this building — the species, size, spacing, and span of the framing, its condition, and the snow load where it stands. There is no table that answers it remotely.

Code and jurisdiction

There is no national building code for site-built houses in the United States. States and local governments adopt model codes and amend them, so the same detail can be required in one place, optional in the next county, and written to a different edition in the state beside it.

Two verifiable examples of the same model code family at different editions: Minnesota Rules part 1309.0010 adopts the 2018 edition of the International Residential Code by reference, while Chapter 51-51 of the Washington Administrative Code is titled the adoption and amendment of the 2021 edition of the International Residential Code. Both are the “IRC.” They are not the same requirements.

Any model-code figure on this page — the 24-inch ice-barrier dimension, the 4-inch step flashing legs — is a model provision quoted from federal technical guidance, not the law where you live. The adopted edition, the local amendments, the effective date, and the authority having jurisdiction decide what actually applies. Confirm with your building department before a provision on a web page becomes a line in your contract.

Maintenance

Roofing materials made before about 1990 — some shingles, felts, mastics, and cements — may contain asbestos, and the risk is in disturbing them. EPA’s guidance on protecting a household says plainly to leave undamaged asbestos-containing materials alone, and lists disturbing, damaging, removing improperly, repairing, cutting, tearing, sanding, sawing, drilling, and scraping as the actions that can release fibers. Separately, EPA says the only way to be sure a material contains asbestos is to have it tested by a qualified laboratory, with samples taken by a properly trained and accredited asbestos professional, and recommends testing suspect material when it is damaged or when a planned renovation would disturb it.

If a roof of that age is coming off, or an existing layer is being cut into, that is a question to settle before the work starts rather than a discovery to make in the middle of it. Do not scrape, break, or sample suspect material yourself.

Warranty and repair

What is covered, and what can actually be repairedSection link

Every warranty on a roof covers some subset of these thirteen parts. Knowing which subset is most of the skill in reading one.

A covering warranty is about the covering: A manufacturer’s document is normally a promise about the product it made, on terms it wrote, subject to installation in accordance with its own instructions. The deck, the framing, the flashings, the ventilation, and the workmanship are typically addressed separately or excluded. That is not a scandal; it is what the document says. The mistake is assuming a product promise covers an assembly.
Enhanced and system coverage buys conditions: Broader coverage usually arrives with requirements attached — specified accessories from the same manufacturer, an installer holding a particular credential, a registration deadline, sometimes a documented ventilation configuration. Those conditions are the price of the coverage, and they are enforceable against you rather than for you if they are not met.
Workmanship is a different promise from a different party: Installation coverage comes from the company that did the work, not from the manufacturer. Its length, what it excludes, and what survives if the company closes or is sold are set by that contract and by the law where the building stands. Ask how long the company has traded under its current name before treating a long workmanship term as meaningful.
The layers most likely to leak are the least likely to be covered: Flashings are frequently the interface between a manufacturer’s product coverage and an installer’s workmanship coverage, which is exactly where responsibility can be disputed. Getting the flashing scope written explicitly — which pieces are new, which are reused, who warrants each — is worth more than an extra decade of nominal product term.

Repairability

Repairability differs sharply by layer, and it is the reason a small problem in one place costs far more than the same-sized problem somewhere else.

Covering: repairable in place if matching units can be found. Color and profile matching gets harder as a product line ages or is discontinued, and a repair patch that does not match is permanently visible.
Flashing: repairable, but properly redoing step flashing means lifting the courses over it and often disturbing the wall cladding, which is why sealant so often appears instead. Sealant is a maintenance item pretending to be a repair.
Underlayment and ice barrier: not repairable without removing the covering above them. In practice they are replaced when the covering is.
Deck: replaceable by the sheet, but only while the covering is off. This is why deck allowances belong in the contract before the job starts, not in a phone call on day two.
Structure: repairable, but it is carpentry or engineering rather than roofing, and it is priced accordingly.

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 to ask an installerSection link

These are anatomy questions, not price questions. A proposal that answers them clearly is comparable to another proposal that answers them clearly; one that does not is not comparable to anything.

What happens if the deck under the covering is not sound, and how is that priced?
Nobody knows the deck condition before tear-off, so this is a question about process, not prediction. A good answer includes a stated unit price for replacement sheathing, who decides what gets replaced, and whether you will be shown it. A vague answer here is how a quote quietly becomes a larger bill.
Which underlayment are you using, by product name, and over how much of the roof?
“Standard underlayment” is not an answer. The product, its type, and its coverage are the second drainage plane on your building for the next few decades, and they are cheap to name in writing.
Is an ice barrier going in at the eaves, how far up the slope, and is that what the building department requires here?
This is a place where the adopted code edition changes the physical roof by a measurable distance. It also tells you whether the installer knows the local amendments or is quoting a habit.
Which flashings are you replacing, and which are you reusing?
Reused step flashing is a legitimate choice in some situations and a false economy in many. Either way the answer should be specific — by location, not as a category — and it should be in the written scope.
Where does kickout flashing go on this roof? Show me on the elevation.
An installer who has looked at your roof can point at the spot. One who has not will answer in general terms. This question is a competence probe as much as a scope question.
What is the intake ventilation on this roof, and is any of it blocked?
Exhaust is easy to sell and easy to see; intake is neither. If the answer is only about ridge vent, the assembly has been half-considered.
Is drip edge included at both the eaves and the rakes, and in what metal and thickness?
Edge metal is inexpensive, is where wind damage starts, and is one of the most commonly omitted line items in a thin proposal.
How are the penetrations being flashed — new boots, or reused ones?
Rubber collars weather from sunlight and thermal cycling and generally reach the end of their useful life before the covering does. Reusing an aged one on a new roof puts the next leak at a point that will be hard to attribute to the job.
If this building predates 1990 and there are existing layers coming off, how is that material handled?
Older roofing materials may contain asbestos, and the exposure comes from disturbing them. A competent contractor has a settled answer about testing and handling. An improvised answer is a reason to pause the job, not to proceed carefully.

Require these in writing

Tear-off: how many existing layers are being removed, and disposal
Deck inspection method and a unit price for replacement sheathing
Underlayment by product name, type, and area covered
Ice barrier by product, and the distance it runs up the slope
Every flashing location, and whether each piece is new or reused
Drip edge at eaves and rakes, with metal and thickness
Valley method: open metal, woven, or closed cut
Penetration flashings: new boots, and how many
Intake and exhaust ventilation, by type and quantity
Gutter work, if any, and where downspouts discharge
Permit responsibility and inspection scheduling
Clean-up, magnet sweep, and site protection

What goes wrong

Misconceptions and failure modesSection link

Six beliefs that quietly cost money, and eight ways this assembly actually comes apart.

Common misconceptions

Common belief
A new roof means everything under it is new.
What is actually true
A replacement normally means new covering, new underlayment, and some new flashing. The deck is reused unless it has failed. The framing is normally untouched. The ventilation may be exactly what it was. Two proposals that both say “new roof” can differ by thousands of dollars of genuinely different work, which is why the nouns in the scope matter more than the headline.
Common belief
Self-adhering membrane over the whole deck makes a roof leakproof.
What is actually true
It is a real upgrade in specific conditions — ice-dam regions, high-wind coastal exposure — and Building America describes fully adhered membrane as one accepted way to seal a deck. It is also not generally required: Building America notes that building codes generally do not require a sealed roof deck for new homes or roof replacements. It is not a substitute for correct flashing, it does not make the covering optional, and it changes how an assembly dries — a building-science question rather than a shopping one.
Common belief
The leak is directly above the ceiling stain.
What is actually true
Water entering at a penetration or a valley runs along the underside of the deck, down a rafter, across a top plate, and drips wherever gravity and framing take it. The stain marks where water left the assembly, not where it entered. This is why chasing a stain from inside without tracing the path above it produces repeated repairs to a roof that is not leaking where it is being repaired.
Common belief
The underlayment is waterproof, so the covering is mostly cosmetic.
What is actually true
Underlayment is a secondary drainage plane, not a finished surface, and it is not intended for long-term exposure to sunlight and weather. It buys time and handles what gets past the covering. It does not replace it.
Common belief
More ventilation is always better.
What is actually true
Ventilation is a means, not a virtue. Its purpose in a vented assembly is to keep the deck near outdoor temperature and to remove incidental moisture. Adding exhaust without matching intake can pull conditioned, humid air out of the house through ceiling leaks, which makes the moisture problem worse. Correctly designed unvented assemblies achieve the same goals with no ventilation at all.
Common belief
Drip edge is trim.
What is actually true
It is the edge detail of the most wind-loaded part of the roof and the piece that keeps water from wicking back onto the fascia. Its cost is trivial next to the repair for the fascia, soffit, and deck edge it protects.

How it actually fails

Sealant standing in for flashing: A bead of caulk or roof cement is applied where a piece of metal belongs, usually at a wall junction or around a penetration. Sealant is a maintenance material: it depends on adhesion, and adhesion is what sunlight, movement, and temperature cycling take away. Metal that is correctly lapped needs no adhesion at all to work, which is why it is the detail and sealant is not.What you can see: Visible black or gray beads at roof-to-wall junctions and around pipes, often reapplied in layers. Photographable from the ground with a zoom lens.
Missing kickout at the bottom of a roof-to-wall run: Water collected along the junction arrives at the eave with nothing to divert it into the gutter, so it runs down behind the cladding. Building America attributes thousands of dollars of homeowner damage to this single omitted piece.What you can see: A vertical stripe of failed paint, staining, or soft cladding on the wall directly below the point where the roof edge meets the wall.
Ice dam at the eave: Heat escaping into the attic warms the deck, snow melts, the meltwater refreezes at the cold overhang, and the resulting dam holds standing water above the eave. Building America identifies air leakage warming the deck as one of the greatest sources of this in residential construction.What you can see: Rows of icicles, ice filling the gutter, and a ceiling stain at the top of an exterior wall that appears during a thaw and dries afterward.
Deck deterioration under a sound-looking covering: Long-term wetting from a small leak, or sheathing that was marginal for its span, softens the deck between rafters. Fasteners lose their grip before the covering looks bad.What you can see: A rippled, quilted, or wavy roof surface visible in raking light from across the street; a plane that no longer reads as flat.
Aged boot flashing at a plumbing vent: Sunlight and thermal cycling crack the rubber collar sealing the flashing to the pipe, typically well before the covering reaches the end of its service life.What you can see: A cracked or slumped collar visible in a zoomed photograph; a recurring ceiling stain near a bathroom or kitchen that is not below any obvious roof damage.
Intake ventilation blocked at the eave: Insulation pushed into the eave, or soffit vents painted or debris-filled, closes the channel that Building America’s ice-dam guidance says should be held open with a 2-inch vent space.What you can see: Soffit vents that look solid rather than open when you stand under the eave; exhaust vents present at the ridge with no visible intake anywhere.
Fasteners in the wrong place: Nails driven above the intended fastening zone, overdriven through the mat, or underdriven so the head stands proud. Each one is a hole in the drainage plane, and the covering above it is no longer mechanically held where it was designed to be held.What you can see: Not visible from the ground on a finished roof. Visible in progress photographs, and visible after the fact as tabs lost in a repeating pattern after a windstorm.
Gutter overflowing at the back edge: A gutter hung too low for the shingle overhang, blocked, or sloped the wrong way sends water behind the gutter instead of into it, soaking the fascia and the deck edge.What you can see: Watch it rain from a window: water sheeting behind the gutter, staining down the fascia, and a saturated line of soil directly under the eave rather than under the downspout.

Sources and further readingSection link

Understanding Roofing / Published August 13, 2026 / Updated August 14, 2026

Scope and limitations

It cannot tell you what is under your covering.
Deck condition, underlayment type, ice-barrier extent, and flashing quality are unknowable from the ground and are usually confirmed only during tear-off.
It carries no cost figures.
Nothing here should be read as a price for any layer or any job.
Every code figure quoted here is a model provision, quoted from federal technical guidance rather than from the law of any jurisdiction.
Only your building department can tell you what is adopted, in which edition, with which amendments, where you are.
The two diagrams are schematics of one common assembly at one pitch.
They are not construction details, they are not to scale, and they must not be used to build or specify anything.
It covers steep-slope residential assemblies.
Low-slope and commercial membrane roofs are a different system with a different layer order and different failure modes.
It cannot assess your building’s structure.
Whether your framing can carry a heavier covering is a question for an engineer looking at this building.

Asphalt Shingle Roofs
U.S. Department of Energy — Building America Solution Center (PNNL) / Updated 2 December 2022
The layer sequence of a shingle roof, deck sealing options, underlayment, ice barrier extent quoting the 2018 IRC, drip edge at eaves and rakes, flashing at penetrations and roof-wall intersections.
Written for asphalt shingle assemblies and referencing model-code text; it is not the adopted code in any jurisdiction.
Roof Deck Sheathing and Sealing for Sloped Roofs
U.S. Department of Energy — Building America Solution Center (PNNL)
Callout 2: minimum 7/16 in. plywood or OSB sheathing and 8d ring-shank attachment at 4 in. on center near edges and ridge, 6 in. elsewhere, and the three accepted methods of sealing the deck.
The sheathing and fastening figures are IBHS recommendations reported by DOE, not a code requirement. Required deck attachment is set by the adopted code and the design wind loads for the site.
Step and Kick-Out Flashing at Roof-Wall Intersections
U.S. Department of Energy — Building America Solution Center (PNNL)
Callouts F and G: step flashing extending at least 4 in. up the wall and 4 in. onto the deck in galvanized steel at least 0.019 in. thick (quoting the 2015 IRC), shingle-fashion lapping with the water-resistive barrier, and the damage attributed to missing kickout flashing.
The dimensional figures are quoted from a model code edition, not from the code adopted where a reader lives.
Roof Valleys and Penetrations Sealed
U.S. Department of Energy — Building America Solution Center (PNNL)
That valleys and penetrations through the roof decking are among the most vulnerable areas for water intrusion; membrane application in valleys lapped 6 in. shingle-fashion; membrane at least 6 in. around penetrations before boot flashing.
Notes that codes generally do not require a sealed roof deck; sealing is presented as beneficial practice in specific hazard regions, not as a universal requirement.
Roof Edge Protection
U.S. Department of Energy — Building America Solution Center (PNNL)
Callout 6: drip edge at eaves and rakes, its lap over the deck and extension below the sheathing, and that roof edges see the highest wind pressures and are where most covering blow-off starts.
Written for high-wind zones and drawing on IBHS FORTIFIED criteria; the specific dimensions are recommendations rather than code determinations.
Construct Roofs and Attics for Ice Dam Prevention
U.S. Department of Energy — Building America Solution Center (PNNL)
Callouts 9, 10 and 11: air leakage warming the deck as one of the greatest sources of ice dams, air sealing as the most important step, the 2-inch vent space, R-60 or greater in climate zones 5 and above for unconditioned ventilated attics, and both ground-snow-load markers (likely above 30 lb/ft², typically prevalent above 60 lb/ft²).
Insulation levels and strategies are climate-zone specific and are guidance, not adopted requirements. The R-60 figure is stated for unconditioned, ventilated attics; it is not a recommendation for unvented roof assemblies.
Gutters and Downspouts
U.S. Department of Energy — Building America Solution Center (PNNL) / Updated 26 September 2021
Callout 7: several thousand gallons of runoff from a few inches of rain, gutter slope of at least 1/16 in. per foot, downspouts every 20 to 50 feet, and discharge at least 5 feet from the foundation or into a catchment at least 10 feet away.
Unvented Attic Insulation
U.S. Department of Energy — Building America Solution Center (PNNL)
That unvented attic assemblies are a recognized approach in which the thermal, air, and moisture control layers move to the roof-deck plane, and that they depend on air-impermeable insulation at a minimum R-value set by climate zone for condensation control.
Describes the strategy and references model-code tables; whether an unvented assembly is permitted, and on what conditions, is a jurisdictional question.
Look for Missing Roof and Wall Flashing
U.S. Department of Energy — Building America Solution Center (PNNL) / Updated 11 September 2025
The observable signs of missing kickout, step, drip edge, and boot flashing, including wall-level discoloration, bubbling paint, and soft or deteriorating cladding.
Parts of this guide assume ladder access to the roof. This page deliberately uses only the observations it describes that can be made from ground level or from a window.
Keeping up with steep slopes
National Roofing Contractors Association — Professional Roofing / March 2013
That NRCA’s steep-slope roof system application recommendations are intended for substrates with a 4:12 (18-degree) slope or greater, and that rapid and complete drainage is essential for water-shedding roof systems.
Trade association guidance, not a code requirement, and the specific recommendations have been revised in later editions of the NRCA manual.
How do I know if I have asbestos in my home?
U.S. Environmental Protection Agency / Updated 2 April 2026
That the only way to be sure a material contains asbestos is laboratory testing, that samples should be taken by a properly trained and accredited asbestos professional, and that testing is recommended when material is damaged or a renovation would disturb it.
This page covers testing only. The instruction to leave undamaged material alone, and the list of actions that release fibers, come from EPA’s separate household-protection page cited below.
Protect Your Family from Exposures to Asbestos
U.S. Environmental Protection Agency / Updated 25 June 2026
That EPA advises leaving undamaged asbestos-containing materials alone, and that fibers may be released when such materials are disturbed, damaged, removed improperly, repaired, cut, torn, sanded, sawed, drilled, or scraped.
General household guidance. It is not a determination about any particular roofing material, and abatement rules are set by state and local programs.
Fall protection in residential construction — guidance
U.S. Occupational Safety and Health Administration
That workers in residential construction six feet or more above a lower level must be protected by guardrails, safety nets, or a personal fall-arrest system under 29 CFR 1926.501(b)(13).
An employer obligation for workers, not a rule that applies to a homeowner. It is cited here as evidence of how seriously the hazard is treated by people who do this for a living.
Minnesota Rules, part 1309.0010 — Adoption of the International Residential Code by reference
Minnesota Office of the Revisor of Statutes
That Minnesota adopts the 2018 edition of the International Residential Code by reference — one half of the worked example showing that “the IRC” means different requirements in different states.
State-level adoption only. Local amendments, later rule changes, and the authority having jurisdiction still govern any specific project.
Chapter 51-51 WAC — Adoption and amendment of the 2021 edition of the International Residential Code
Washington State Legislature / Chapter page last updated 30 January 2024
That Washington adopts and amends the 2021 edition of the International Residential Code — the other half of the worked example on code edition variation.
State-level adoption only, and the chapter contains state amendments that change the model text. Local jurisdictions and the authority having jurisdiction still govern.

Suggest a correction