For roofing contractors, inspectors, and adjusters

The defect is easy to see. Naming its cause is the hard part.

Practitioner reference · steep-slope asphalt, with notes where other systems differ

A working catalogue of the defects that generate callbacks, denied warranty claims and disputed adjustments — written for people who install and assess roofs, not for people who own one.

30-second answer

What caused this defect, and which of the three parties owns it?

Most roofing defects trace to workmanship, to a material or manufacturing fault, or to ordinary weathering — and appearance alone rarely tells you which. Pattern and timing do. The catalogue below gives each defect's appearance, mechanism, cause class, what reveals it, and what prevents it, because the cause class decides who pays.

Safety first

Confirming almost anything in this catalogue means being on the roof, and that is where the fall exposure is

Under OSHA’s construction fall-protection standard, each employee on a steep roof — defined at 29 CFR 1926.500(b) as a slope greater than 4 in 12 — with unprotected sides and edges 6 feet or more above lower levels must be protected by guardrails with toeboards, safety nets, or a personal fall arrest system (1926.501(b)(11)). Residential construction carries the same 6-foot trigger under 1926.501(b)(13), and OSHA rescinded the old interim residential guidelines in STD 03-11-002: an employer who cannot use conventional fall protection must demonstrate infeasibility or greater hazard and implement a written plan meeting 1926.502(k).

One nuance matters for inspectors and adjusters specifically. The scope statement at 1926.500(a) says Subpart M does not apply to employees making an inspection, investigation or assessment of workplace conditions before construction work starts or after all of it is finished. That is a statement about which standard governs, not a statement that the roof is safe or that nothing else applies. Applicability turns on the work, the employer, and whether the state runs its own OSHA-approved plan. This page publishes no compliance determination for any employer.

Plan the access before the assessment. Fall protection on roofing work covers anchors, systems and the standards that apply.

Learning paths and saved lessons

At a glance

The short versionSection link

This is a reference page. It is built to be looked things up in, not read start to finish.

Defects catalogued: 14Each with appearance, mechanism, cause class, what reveals it, and what prevents it.
Cause classes used: Four, and a fifth thing that is not oneWorkmanship, material, design, maintenance — plus ageing, which is not a defect at all. Filing ageing as a defect, or a design fault as workmanship, is the error all three of this page's audiences make most often.
The evidence that decides the class: Pattern, timing, correlationUniform and early points at material or design. Clustered by slope, elevation or day's work points at workmanship. Orientation-dependent and gradual points at ageing.
What governs installation: The instructions on the wrapperThe published instructions for that specific product, together with the adopted code in that jurisdiction. Not a house method, and not this page.
What this page does not do: It does not determine a causeIt ranks probabilities from patterns. A destructive investigation, a lab evaluation of the material, or a manufacturer's own determination is what settles a disputed cause.

Tradeoffs

When this catalogue is the right tool, and when it is notSection link

Best when

You are running in-progress QC and want the checkpoints ordered by what actually generates callbacks rather than by trade sequence.
You are writing an inspection report and need language that keeps the observation separate from the inferred cause.
You are assessing a claim and need to know which conditions are consistent with a dated weather event and which were installed that way.
You are bringing a foreman up and want the mechanism behind each rule, because a rule without its mechanism gets dropped the first time it is inconvenient.

Think twice if

The roof is not steep-slope asphalt. Most mechanisms transfer; almost none of the dimensions do.
You need a determination that will hold up under challenge. This page reasons from pattern; a destructive investigation settles it.
The product's own instructions say something different. They govern, and this page does not.
You want a percentage. There is no public dataset apportioning roof failures by cause, and this page will not invent one.

What changes the answer

The adopted code edition and local amendments — every code-shaped statement here is model text until you check what your jurisdiction actually adopted.
Climate. A defect that takes fifteen years to produce a leak in a dry heat zone produces one in three winters in a freeze-thaw belt.
Whether the roof was ever maintained, and whether anyone can prove it either way.
Whether anyone photographed the deck. Most arguments in this catalogue are settled by tear-off photographs that were never taken.

The distinction that decides the outcome

Four classes of defect, and one thing that is not a defectSection link

Workmanship, material, design, maintenance — and ageing. Confusing the last one for any of the others is how a warranty claim gets denied and a reputation gets spent.

Section through a shingle and deck at four fastener seatings. Panels 2, 3 and 4 are the three ways a nail can be present and still not be doing its job.Original diagram, Understanding Roofing. The four seatings are the ones drawn in the IKO Cambridge application instructions and in the CertainTeed Master Craftsman manual; the drawing is ours.

A defect catalogue is only useful if the entries carry a cause, and a cause is only useful if it survives an argument. Three parties read the same roof and want three different answers out of it: the contractor wants to know whether this is a callback, the inspector wants to describe what is there without asserting more than the evidence supports, and the adjuster wants to know whether the condition predates the loss. All three are asking the same underlying question, which is what class of cause produced it.

The four classes

Workmanship is a departure from the product’s published instructions or from the adopted code during installation. It is the largest class by count and it is the one a contractor controls completely.

Material is a fault in the product as manufactured. Standard shingle warranties are written against this class and largely only this class: CertainTeed’s applicator manual states plainly that “standard shingle manufacturer warranties tend to cover manufacturing defects,” and that some cover them only where an actual leak results.

Design is a fault in what was specified or in the geometry of the building — a valley discharging onto a wall with no way out, an attic with exhaust and no intake, a slope below the product’s minimum. Design defects get misfiled as workmanship routinely, because the roofer is the last trade on site and the easiest to bill.

Maintenance is a fault in what was or was not done afterwards: a boot left past its service, a sealant repair that became the waterproofing, debris blocking a valley, an intake vent insulated over during an energy retrofit.

And ageing, which is none of them

Granule shedding, mat embrittlement, sealant strip weakening, gradual curling and cupping at the ends of a covering’s service life are weathering. They are the expected behaviour of an organic-bound mineral product exposed to UV and thermal cycling for two decades, and they are not defects in anybody. Presenting them as a manufacturing defect wastes a claim; presenting them as workmanship wastes a contractor. See roof service life for why a warranty term and a service life are different numbers that happen to share units.

The practical test is orientation and gradient. Weathering loads a roof unevenly and predictably: south and west elevations take more UV and more thermal cycling than north ones, and a condition that is severe on one and absent on the other is behaving like weathering. A manufacturing fault does not care which way a plane faces. Neither does a nail gun.

The catalogue

Fourteen defects, with cause and preventionSection link

Ordered by where they occur in the assembly rather than by frequency, because no public dataset supports a frequency ordering.

Steep-slope roofing defect catalogue. 'What reveals it' names the event that brings the defect to light, not a number of years — no dataset supports a national time-to-failure figure for any of these. Cause classes are this page's own analysis of where the defect usually originates, not a determination about any particular building.
Defect	What you see	Mechanism	Cause class	What reveals it	What prevents it
High nailing	Nail heads at or above the sealant line when a course is lifted; shingles that never sealed; blow-off in strips rather than singles.	The fastener lands in or above the sealant strip instead of the nailing zone, so the course above cannot bond and the course below is held only by its own nails.	Workmanship	The first strong wind before the roof has sealed.	Nail to the printed nail line for that product, not to a habit carried from another one. Gun swung from the waist, not the shoulder.
Overdriven fasteners	Head sunk below the shingle surface; the mat dished or cut around it.	The head is driven through the mat, so it no longer bears on sound material and the shingle can pull through over it. The torn mat also leaves a penetration the course above has to keep dry on its own.	Workmanship — usually equipment	Wind uplift first; nail-hole leaks much later.	Reset gun pressure as the temperature moves through the day; hand-nail in the cold. Seal a head already overdriven and set another fastener beside it.
Underdriven fasteners and shiners	Heads standing proud; a bump telegraphing through the course above; nails backing out.	A proud head holds the covering shingle off the one below and wears through it from underneath. A shiner has missed the framing and holds nothing at all.	Workmanship	The first hot spell, as the courses relax onto the proud heads; wear-through much later.	Hammer proud heads flush. Pull and replace fasteners that missed a rafter rather than leaving them.
Missing or insufficient starter course	First course laid straight onto underlayment; no sealant band at eave or rake; butts lifting along the edge.	The starter supplies the sealant band that bonds the first course and closes the joints between first-course shingles. Without it the eave and rake is an unbonded flap.	Workmanship	The first real wind, at the edge.	Starter at eaves and at rakes, overhanging the drip edge by the dimension the instructions give — the high-wind warranty on some products is conditioned on it.
Incorrect exposure	Course lines that drift; short head lap; the job finishing with material left over.	Exposure sets head lap and where the covering course lands relative to the nailing zone. Every half inch of exposure costs a whole inch of head lap, because head lap is the height less twice the exposure; run short and you spend material and course count instead.	Workmanship	Wind-driven rain — and a bundle count that will not reconcile.	Chalk every course or use a gauged pattern. The exposure is the figure on the wrapper for that product, not a remembered number.
Reused or omitted flashing	Pitted or patched metal under a new roof; sealant where a counterflashing should be; a new roof running to a wall with no metal at all.	Flashings are what let the covering stop being continuous. Metal carried over from the old roof brings its old fastener holes, its corrosion and its original geometry into an assembly meant to outlive it.	Workmanship, often decided in the estimate	The first wind-driven rain, or the first freeze–thaw cycle.	Price flashing replacement into the scope. Model text in the commercial code — IBC 2018 §1511.5 — does not permit rusted, damaged or deteriorated vent flashings, edge metal, counterflashings, drain outlets or collars to be reinstalled. What binds is whatever the jurisdiction adopted.
Missing kickout flashing	Nothing at the bottom of a roof-to-wall run; staining, rot or a repair in the wall below.	Runoff concentrated in the roof-wall intersection reaches the bottom of the run and, with nothing to turn it out, goes behind the cladding instead of into the gutter.	Workmanship, sometimes design	Often years later, and behind cladding that hides it.	A kickout at the bottom of every roof-to-wall run, lapped into the wall's own drainage plane.
Improper valley treatment	Fasteners near the valley centre; a closed-cut valley on a product that calls for open metal; lining that does not run through; cement in the channel.	The valley carries two planes of runoff through one channel. A fastener in the channel, or a lining that stops short, puts a hole in the highest-volume path on the roof.	Workmanship, sometimes product selection	Heavy rain, and ice.	Build the valley before the field; keep fasteners clear of the centre by the dimension the instructions give; use the valley type the product allows.
Inadequate or unbalanced ventilation	Ridge vent over blocked or painted-shut soffits; gable vents left open alongside it; rusted nail points and stained sheathing in the attic.	Effective ventilation is limited by whichever of intake and exhaust is smaller. Two kinds of exhaust on one attic short-circuit the intended low-to-high draft and can draw weather in.	Design, workmanship or maintenance — often all three	The first cold season as sheathing condensation; over years as deck decay.	Balance the areas, open and baffle the intake, remove or block the other exhausts. A correctly designed unvented assembly is a legitimate alternative, not a failure.
Sealant used as primary waterproofing	A bead where metal should be; cement smeared over a valley, a boot or a wall line; a thick, lumpy or blistered surface.	Sealant is an accessory to a geometry that already sheds water. Made the water barrier, it becomes the only barrier, and it then fails on a schedule set by movement and UV rather than by the roof.	Workmanship, or a maintenance decision	Whenever the bead first cracks or moves. No interval is published, by anyone.	Fix the geometry. Where cement is specified — hand-sealing, valley ends, exposed cap nails — use the quantity the instructions give, because excess causes blistering.
Penetration boot failure	Split or perished collar; collar shrunk back off the pipe; a boot that has been caulked instead of replaced.	The collar is the thinnest and most highly strained elastomer on the roof, unshaded and unprotected by granules, so it ages faster than the covering around it.	Material ageing first, maintenance later	Rain, once the split opens. The stain appears downslope of the pipe, not under it.	Flash the penetration with membrane under the boot, and treat the boot as a wear item on its own replacement cycle rather than as part of the covering.
Ice-barrier omission where required	No self-adhered membrane at the eave where the jurisdiction requires one; a leak line that runs along the eave rather than from a point.	Meltwater held behind an ice dam stands against a covering that sheds water rather than resisting it, and enters at the laps.	Workmanship, or a scope decision	The first thaw after the first sustained cold spell.	Read the adopted code for the jurisdiction and install to the extent it gives — the model provision measures inside the exterior wall line, not from the fascia. The membrane treats a symptom; air sealing and insulation treat the cause.
Deck fastening deficiencies	Panels that move underfoot; shiners visible from the attic; panels butted tight; wide board decking under a new roof.	The deck is what everything else is fastened to. Fasteners that miss framing take load out of the assembly; panels butted tight buckle when they take up moisture; wide boards move further than shingles can follow.	Workmanship, sometimes original construction	Uplift in a wind event; buckling in the first humid season.	Re-nail to the spacing the job actually requires, keep the panel gap, and overlay or kerf wide board decks before the covering goes on.
Dissimilar-metal contact	Corroded fasteners in otherwise sound flashing; a halo of corrosion where two metals meet; aluminium wasting beneath a copper element.	Two metals in contact, or linked by runoff, form a cell and the less resistant one corrodes. The further apart they sit on the galvanic scale, the faster it goes.	Workmanship — material selection at the detail	Years — and much sooner near salt water.	Fasteners of the same metal as the flashing they penetrate; unavoidable pairs isolated with underlayment, bituminous paint or another non-conducting material.

Read this table one item at a time

High nailing

What you see: Nail heads at or above the sealant line when a course is lifted; shingles that never sealed; blow-off in strips rather than singles.
Mechanism: The fastener lands in or above the sealant strip instead of the nailing zone, so the course above cannot bond and the course below is held only by its own nails.
Cause class: Workmanship
What reveals it: The first strong wind before the roof has sealed.
What prevents it: Nail to the printed nail line for that product, not to a habit carried from another one. Gun swung from the waist, not the shoulder.

Overdriven fasteners

What you see: Head sunk below the shingle surface; the mat dished or cut around it.
Mechanism: The head is driven through the mat, so it no longer bears on sound material and the shingle can pull through over it. The torn mat also leaves a penetration the course above has to keep dry on its own.
Cause class: Workmanship — usually equipment
What reveals it: Wind uplift first; nail-hole leaks much later.
What prevents it: Reset gun pressure as the temperature moves through the day; hand-nail in the cold. Seal a head already overdriven and set another fastener beside it.

Underdriven fasteners and shiners

What you see: Heads standing proud; a bump telegraphing through the course above; nails backing out.
Mechanism: A proud head holds the covering shingle off the one below and wears through it from underneath. A shiner has missed the framing and holds nothing at all.
Cause class: Workmanship
What reveals it: The first hot spell, as the courses relax onto the proud heads; wear-through much later.
What prevents it: Hammer proud heads flush. Pull and replace fasteners that missed a rafter rather than leaving them.

Missing or insufficient starter course

What you see: First course laid straight onto underlayment; no sealant band at eave or rake; butts lifting along the edge.
Mechanism: The starter supplies the sealant band that bonds the first course and closes the joints between first-course shingles. Without it the eave and rake is an unbonded flap.
Cause class: Workmanship
What reveals it: The first real wind, at the edge.
What prevents it: Starter at eaves and at rakes, overhanging the drip edge by the dimension the instructions give — the high-wind warranty on some products is conditioned on it.

Incorrect exposure

What you see: Course lines that drift; short head lap; the job finishing with material left over.
Mechanism: Exposure sets head lap and where the covering course lands relative to the nailing zone. Every half inch of exposure costs a whole inch of head lap, because head lap is the height less twice the exposure; run short and you spend material and course count instead.
Cause class: Workmanship
What reveals it: Wind-driven rain — and a bundle count that will not reconcile.
What prevents it: Chalk every course or use a gauged pattern. The exposure is the figure on the wrapper for that product, not a remembered number.

Reused or omitted flashing

What you see: Pitted or patched metal under a new roof; sealant where a counterflashing should be; a new roof running to a wall with no metal at all.
Mechanism: Flashings are what let the covering stop being continuous. Metal carried over from the old roof brings its old fastener holes, its corrosion and its original geometry into an assembly meant to outlive it.
Cause class: Workmanship, often decided in the estimate
What reveals it: The first wind-driven rain, or the first freeze–thaw cycle.
What prevents it: Price flashing replacement into the scope. Model text in the commercial code — IBC 2018 §1511.5 — does not permit rusted, damaged or deteriorated vent flashings, edge metal, counterflashings, drain outlets or collars to be reinstalled. What binds is whatever the jurisdiction adopted.

Missing kickout flashing

What you see: Nothing at the bottom of a roof-to-wall run; staining, rot or a repair in the wall below.
Mechanism: Runoff concentrated in the roof-wall intersection reaches the bottom of the run and, with nothing to turn it out, goes behind the cladding instead of into the gutter.
Cause class: Workmanship, sometimes design
What reveals it: Often years later, and behind cladding that hides it.
What prevents it: A kickout at the bottom of every roof-to-wall run, lapped into the wall's own drainage plane.

Improper valley treatment

What you see: Fasteners near the valley centre; a closed-cut valley on a product that calls for open metal; lining that does not run through; cement in the channel.
Mechanism: The valley carries two planes of runoff through one channel. A fastener in the channel, or a lining that stops short, puts a hole in the highest-volume path on the roof.
Cause class: Workmanship, sometimes product selection
What reveals it: Heavy rain, and ice.
What prevents it: Build the valley before the field; keep fasteners clear of the centre by the dimension the instructions give; use the valley type the product allows.

Inadequate or unbalanced ventilation

What you see: Ridge vent over blocked or painted-shut soffits; gable vents left open alongside it; rusted nail points and stained sheathing in the attic.
Mechanism: Effective ventilation is limited by whichever of intake and exhaust is smaller. Two kinds of exhaust on one attic short-circuit the intended low-to-high draft and can draw weather in.
Cause class: Design, workmanship or maintenance — often all three
What reveals it: The first cold season as sheathing condensation; over years as deck decay.
What prevents it: Balance the areas, open and baffle the intake, remove or block the other exhausts. A correctly designed unvented assembly is a legitimate alternative, not a failure.

Sealant used as primary waterproofing

What you see: A bead where metal should be; cement smeared over a valley, a boot or a wall line; a thick, lumpy or blistered surface.
Mechanism: Sealant is an accessory to a geometry that already sheds water. Made the water barrier, it becomes the only barrier, and it then fails on a schedule set by movement and UV rather than by the roof.
Cause class: Workmanship, or a maintenance decision
What reveals it: Whenever the bead first cracks or moves. No interval is published, by anyone.
What prevents it: Fix the geometry. Where cement is specified — hand-sealing, valley ends, exposed cap nails — use the quantity the instructions give, because excess causes blistering.

Penetration boot failure

What you see: Split or perished collar; collar shrunk back off the pipe; a boot that has been caulked instead of replaced.
Mechanism: The collar is the thinnest and most highly strained elastomer on the roof, unshaded and unprotected by granules, so it ages faster than the covering around it.
Cause class: Material ageing first, maintenance later
What reveals it: Rain, once the split opens. The stain appears downslope of the pipe, not under it.
What prevents it: Flash the penetration with membrane under the boot, and treat the boot as a wear item on its own replacement cycle rather than as part of the covering.

Ice-barrier omission where required

What you see: No self-adhered membrane at the eave where the jurisdiction requires one; a leak line that runs along the eave rather than from a point.
Mechanism: Meltwater held behind an ice dam stands against a covering that sheds water rather than resisting it, and enters at the laps.
Cause class: Workmanship, or a scope decision
What reveals it: The first thaw after the first sustained cold spell.
What prevents it: Read the adopted code for the jurisdiction and install to the extent it gives — the model provision measures inside the exterior wall line, not from the fascia. The membrane treats a symptom; air sealing and insulation treat the cause.

Deck fastening deficiencies

What you see: Panels that move underfoot; shiners visible from the attic; panels butted tight; wide board decking under a new roof.
Mechanism: The deck is what everything else is fastened to. Fasteners that miss framing take load out of the assembly; panels butted tight buckle when they take up moisture; wide boards move further than shingles can follow.
Cause class: Workmanship, sometimes original construction
What reveals it: Uplift in a wind event; buckling in the first humid season.
What prevents it: Re-nail to the spacing the job actually requires, keep the panel gap, and overlay or kerf wide board decks before the covering goes on.

Dissimilar-metal contact

What you see: Corroded fasteners in otherwise sound flashing; a halo of corrosion where two metals meet; aluminium wasting beneath a copper element.
Mechanism: Two metals in contact, or linked by runoff, form a cell and the less resistant one corrodes. The further apart they sit on the galvanic scale, the faster it goes.
Cause class: Workmanship — material selection at the detail
What reveals it: Years — and much sooner near salt water.
What prevents it: Fasteners of the same metal as the flashing they penetrate; unavoidable pairs isolated with underlayment, bituminous paint or another non-conducting material.

Dimensions, fastener counts and exposures are set by the published instructions for the specific product and by the code the jurisdiction adopted. Where those disagree with anything above, they govern. Terms are defined in the glossary — overdriven, underdriven, shiner, nailing zone, headlap, kickout, net free area.

Reading the evidence

What the pattern tells you about the causeSection link

These are priors, not determinations. Each one is worth stating in a report together with the thing that would overturn it.

Observation patterns and the cause class each one points toward, with the condition that would overturn the inference. Original analysis, Understanding Roofing.
What you observe	Points toward	Why	What would overturn it
Uniform across every plane and elevation, present from the first year	Material or design	A crew's error rate varies with fatigue, weather and body position. A manufacturing or design fault does not vary at all.	One crew installed the whole roof in one day under one set of conditions, in which case a uniform workmanship error is entirely possible.
Clustered on one slope, one elevation, or one day's run	Workmanship	Distribution follows the people and the sequence, not the building's exposure or the product's chemistry.	The clustered area is also the area with a different exposure, a different slope, or a different detail — in which case design is back in play.
Concentrated at walls, penetrations, valleys and edges	Workmanship or design	Interruptions are where the shedding logic stops and someone has to make a decision. The field mostly takes care of itself.	The interruptions are also the oldest part of the assembly — reused flashing puts age and workmanship in the same place.
Worse on south and west elevations, absent on north	Ageing	UV dose and thermal cycling are orientation-dependent. A material fault and a nail gun are not.	The building is shaded on one side by something that was not there for most of the roof's life.
Appeared abruptly after a dated weather event, with directional bias	A dated event, not a defect	Storm damage arrives at once and with a bearing. Defects arrive gradually and without one.	The roof had a pre-existing defect that determined which units failed — both can be true, and usually the argument is about proportion.
Present only where a detail was worked on later	Maintenance	The defect boundary follows an earlier repair boundary rather than an installation boundary.	The 'repair' was actually part of the original installation, done by a different crew on the same job.
Units from one lot behave differently from the rest	Material	Manufacturing variation is batch-structured. Nothing else on a roof is.	The bundles came from different lots because they came from different suppliers, which also means different delivery, storage and handling.

Read this table one item at a time

Uniform across every plane and elevation, present from the first year

Points toward: Material or design
Why: A crew's error rate varies with fatigue, weather and body position. A manufacturing or design fault does not vary at all.
What would overturn it: One crew installed the whole roof in one day under one set of conditions, in which case a uniform workmanship error is entirely possible.

Clustered on one slope, one elevation, or one day's run

Points toward: Workmanship
Why: Distribution follows the people and the sequence, not the building's exposure or the product's chemistry.
What would overturn it: The clustered area is also the area with a different exposure, a different slope, or a different detail — in which case design is back in play.

Concentrated at walls, penetrations, valleys and edges

Points toward: Workmanship or design
Why: Interruptions are where the shedding logic stops and someone has to make a decision. The field mostly takes care of itself.
What would overturn it: The interruptions are also the oldest part of the assembly — reused flashing puts age and workmanship in the same place.

Worse on south and west elevations, absent on north

Points toward: Ageing
Why: UV dose and thermal cycling are orientation-dependent. A material fault and a nail gun are not.
What would overturn it: The building is shaded on one side by something that was not there for most of the roof's life.

Appeared abruptly after a dated weather event, with directional bias

Points toward: A dated event, not a defect
Why: Storm damage arrives at once and with a bearing. Defects arrive gradually and without one.
What would overturn it: The roof had a pre-existing defect that determined which units failed — both can be true, and usually the argument is about proportion.

Present only where a detail was worked on later

Points toward: Maintenance
Why: The defect boundary follows an earlier repair boundary rather than an installation boundary.
What would overturn it: The 'repair' was actually part of the original installation, done by a different crew on the same job.

Units from one lot behave differently from the rest

Points toward: Material
Why: Manufacturing variation is batch-structured. Nothing else on a roof is.
What would overturn it: The bundles came from different lots because they came from different suppliers, which also means different delivery, storage and handling.

None of these is proof. Each is a reason to look somewhere specific next, and a report is stronger for saying which one it relied on.

Worked example

What half an inch of exposure actually costsSection link

Exposure drift is the catalogue entry people take least seriously, because a roof run half an inch long looks fine from the driveway and the crew finishes early. Here is the arithmetic, using one manufacturer’s published specification so the derivation can be checked against its own printed coverage figure.

The identity

Coverage is width multiplied by exposure, multiplied by the number of shingles. Owens Corning publishes a nominal 13¼ by 39⅜ inch shingle at 5⅝ inch exposure, 64 shingles per square, covering 98.4 square feet:

39.375 in × 5.625 in = 221.48 sq in = 1.5381 sq ft per shingle
1.5381 sq ft × 64 = 98.4 sq ft

That reproduces the published figure exactly, which is the point of doing it: the identity is right, so it can be trusted at a different exposure.

Now run it half an inch long

A chalk line set at 6⅛ inches instead of 5⅝ — half an inch, which is well within what a tired crew does on a long rake without noticing:

39.375 in × 6.125 in = 241.17 sq in = 1.6748 sq ft
1.6748 sq ft × 64 = 107.2 sq ft per square of material

So each square of shingles now covers 107.2 square feet instead of 98.4, which is 8.9 percent more. On a 3,000 square foot roof surface:

3,000 ÷ 98.4 = 30.5 squares at the published exposure
3,000 ÷ 107.2 = 28.0 squares at 6⅛ inches

Two and a half squares — about seven and a half bundles — left on the ground at the end of the job. That is the tell, and it is the only one available from the driveway. If a crew consistently finishes with material left over and the takeoff was right, the exposure is running long.

What it costs on the roof

Two different overlaps move, and they do not move by the same amount. The top lap — the shingle height minus the exposure, the part of a shingle the course above covers — goes from 13.25 − 5.625 = 7.625 inches to 13.25 − 6.125 = 7.125 inches. Half an inch less, as you would expect. Head lap is a different measurement: the overlap between a course and the course two below it, which is the height minus twice the exposure. It takes the loss twice over.

13.25 in − (2 × 5.625 in) = 2.00 in of head lap
13.25 in − (2 × 6.125 in) = 1.00 in of head lap

Half an inch of chalk-line drift halves the head lap on this product. Head lap, not the visible surface, is the redundancy that keeps an overlapping roof watertight when water runs sideways or backs up behind ice — and it is gone on every course, on every plane, for the life of the roof, with nothing about the finished surface to show it.

The second cost is harder to see and worse. The nailing zone sits a fixed distance above the exposure line. Add half an inch of exposure and you have spent half an inch of that distance — the fasteners are in the same place on the shingle, but the course above now covers half an inch less of it. Whether that still leaves the fasteners covered depends on the clearance the product’s own nail line was drawn with, which is printed on that shingle and differs between products. Read it off the shingle rather than off a rule of thumb.

Running short is not the safe error either, though it fails differently. Head lap goes up, which is harmless; what costs is material, labour and the course count, and a run that arrives at the ridge on a different line from the one next to it. Neither direction is free, and only one of them is invisible.

The same arithmetic explains why high nailing is a defect

Keep the same 13¼ inch shingle at 5⅝ inch exposure and measure everything from the butt of one course. The shingle in the course immediately below has its butt 5.625 inches lower, so its top edge sits at 13.25 − 5.625 = 7.625 inches in this course’s frame. A fastener placed below that line passes through two shingles. A fastener placed above it passes through one.

That is the whole mechanism. A nail on the printed line holds the shingle it is driven through and the head of the shingle under it. Move it an inch and a half up — which a gun swung from the shoulder rather than the waist does without anyone noticing — and it is past 7.625 inches, holding one shingle instead of two. It is also in the territory CertainTeed’s manual rules out on a second ground: fasteners “should not go into, above, or between the self-sealing strips,” because if they do “the shingles may not seal properly and will be more likely to blow off.” That same sentence carves out one of the manual’s own products by name, which is a useful reminder that even a manufacturer’s general rule is not general: the sheet for the product on the roof is the one that governs. The course below has lost half its attachment either way, and nobody finds out until the wind arrives. The numbers change product by product; the geometry does not.

One shingle in elevation. Height and exposure line are to the proportions of a 13¼ inch shingle at 5⅝ inch exposure; the sealant and nailing bands are indicative. Fastener 1 is inside the nailing zone; 2 is high, in the sealant strip, where the course above cannot bond over it; 3 is low, in the part of the shingle that stays exposed to weather.Original diagram, Understanding Roofing. Only the shingle height and the exposure line are drawn to scale — where the nailing zone and the sealant strip actually sit is printed on the product, and that is the one that governs.

One entry that needs a table of its own

Dissimilar metals, and which one goes firstSection link

The dissimilar-metal entry is the only defect in the catalogue that is decided entirely at the moment somebody reaches into the wrong pouch.

CertainTeed’s applicator manual publishes a galvanic scale and states the rule plainly: “When any two of the metals noted are in direct contact, the metal lowest on the list will corrode. The farther apart the metals are on the list, the faster corrosion occurs.” Its published order, from lowest resistance to galvanic corrosion to highest, is aluminium, zinc, steel, stainless steel, tin, lead, brass, copper, bronze. The manual also notes that the metals need not be touching: contact “or” a link by electroconductivity “such as occurs through water” is enough, which is what makes runoff from a copper element onto something less resistant a live problem rather than a theoretical one. See galvanic corrosion and fastener metal.

Common pairings on a steep-slope roof, applying the rule and the ordering published in CertainTeed's Master Craftsman Shingle Applicator's Manual, 16th edition (2023). The pairings and the field notes are ours; the scale and the remedies are theirs.
Pairing	Which one corrodes	Where it shows up	What the source says to do
Copper flashing, steel fasteners	The steel nails	Chimney and valley flashings fastened with whatever was in the pouch. The metal is sound and the fasteners are gone.	Use fasteners of the same metal as the flashing they penetrate — copper nails with copper flashing.
Aluminium flashing, copper anywhere upslope	The aluminium	Aluminium drip edge or step flashing beside copper gutters, or downslope of a copper element.	Isolate the pair with underlayment, bituminous paint, or another non-conducting material.
Aluminium flashing, steel fasteners	The aluminium	Aluminium flashing fastened with galvanised or plain steel roofing nails, most visibly within a few miles of salt water.	Aluminium or galvanised nails with aluminium flashing.
Copper or bronze component, steel fastener	The steel	Copper gutters hung on steel brackets; steel screws through a copper or bronze component.	Match the fastener to the flashing metal, or isolate.
Runoff from a more resistant metal onto a less resistant one	The lower metal, wherever the water lands	A copper roof element, a copper valley, or a copper chimney cap discharging onto galvanised or aluminium below it.	Treat runoff as contact — the manual counts a link 'by electroconductivity, such as occurs through water'.

Read this table one item at a time

Copper flashing, steel fasteners

Which one corrodes: The steel nails
Where it shows up: Chimney and valley flashings fastened with whatever was in the pouch. The metal is sound and the fasteners are gone.
What the source says to do: Use fasteners of the same metal as the flashing they penetrate — copper nails with copper flashing.

Aluminium flashing, copper anywhere upslope

Which one corrodes: The aluminium
Where it shows up: Aluminium drip edge or step flashing beside copper gutters, or downslope of a copper element.
What the source says to do: Isolate the pair with underlayment, bituminous paint, or another non-conducting material.

Aluminium flashing, steel fasteners

Which one corrodes: The aluminium
Where it shows up: Aluminium flashing fastened with galvanised or plain steel roofing nails, most visibly within a few miles of salt water.
What the source says to do: Aluminium or galvanised nails with aluminium flashing.

Copper or bronze component, steel fastener

Which one corrodes: The steel
Where it shows up: Copper gutters hung on steel brackets; steel screws through a copper or bronze component.
What the source says to do: Match the fastener to the flashing metal, or isolate.

Runoff from a more resistant metal onto a less resistant one

Which one corrodes: The lower metal, wherever the water lands
Where it shows up: A copper roof element, a copper valley, or a copper chimney cap discharging onto galvanised or aluminium below it.
What the source says to do: Treat runoff as contact — the manual counts a link 'by electroconductivity, such as occurs through water'.

CertainTeed's ordering is its own, and other published galvanic series place some of these metals — stainless steel in particular — in a different order. This table relies on that ordering only for aluminium, steel and copper, which every published series ranks the same way. What is not in dispute is the direction: the less resistant metal in a pair is the one that goes, and the fastener is usually the smallest piece of metal in the joint, so it goes first regardless of which side of the rule it is on. For any pairing involving stainless steel, lead, tin or zinc, check the series the flashing manufacturer publishes for its own product rather than reasoning from this one.

One more that needs unpacking

Why unbalanced ventilation is a defect and more ventilation is not a fixSection link

The ventilation entry is the one most likely to be argued about, because it is the only defect in the catalogue where the obvious remedy makes things worse. CertainTeed’s manual states the rule that explains it: half the vent area must be high in the attic and half low, and “without that balance, the area of effective ventilation is limited to the lesser of the two vent areas.” Its worked illustration is that if 75 percent of the venting is high and 25 percent low, ventilation is limited to the air moving through the lower vents.

Which means adding exhaust to an attic with blocked intake buys nothing. The system is already limited by the intake. It also means the commonest field mistake is a second kind of exhaust: the manual is categorical — “NEVER MIX TWO TYPES OF EXHAUST VENTS” — because gable vents, roof louvers, turbines or a power fan left in place alongside a new ridge vent “will shortcut the low-to-high draft and diminish the ventilation effectiveness,” and can draw weather in through the opening that is now acting as an intake.

The DOE Building America Solution Center puts numbers on the geometry: upper vents should carry no more than 50 percent and no less than 40 percent of the required area, sit at least 3 feet above the lower vents and no more than 3 feet below the highest point of the roof. It also makes the point that a vent’s nominal size is not its net free area — most screened vents run about 60 percent free, so a required 303 square inches of net free area needs roughly 505 square inches of vent.

None of which makes ventilation universally required or universally right. A correctly designed unvented assembly is a recognised approach, and converting an attic halfway — sealing the soffits without building the unvented assembly, or insulating over the intake during an energy retrofit — is how a legitimate design becomes a defect. See ventilation for the system, and unvented attic for the definition.

Where this page is wrong

The conditions under which this catalogue misleads youSection link

The cause-class priors break on a two-crew roof. The clustering logic assumes distribution follows people and sequence. Two crews, a subcontracted tear-off, or one detail repeated by the same person on every elevation all produce distributions that look like the wrong class.

The prevention column assumes the crew controls the variable. On a re-roof over a deck that is out of plane, exposure drift is the deck’s doing, not the chalk line’s. On a building with no soffit, intake is an architectural problem before it is a roofing one. Naming those as workmanship defects is exactly the misfiling this page is against.

“Sealant is not waterproofing” is too strong in some places. On metal and low-slope details, a sealant or butyl tape is a specified, engineered component of the assembly with a published joint design behind it. The catalogue entry is about sealant substituting for geometry, not about sealant existing.

Multiple defects rarely have a single answer. On a nine-year-old roof carrying three of these at once, the honest finding is often that none of them alone caused the leak and the interaction did. A report that picks one because a report needs one is producing confidence it has not earned.

Everything here is steep-slope asphalt unless it says otherwise. The mechanisms generalise; the dimensions do not, and low-slope membrane assemblies fail in a different vocabulary entirely. Start from commercial roof condition assessment for those.

A note on whose side this is

This site is not your business partner, and it says so hereSection link

The rest of this site is written for the person buying a roof. It teaches them to ask for the deck photographs, to check the starter course at the rake, to ask which valley method the product allows, and to notice when a proposal prices new flashing and when it quietly does not. This page hands the trade the same catalogue from the other side. That is deliberate, and it does not come with an apology: a defect catalogue that only one party can read is a worse document.

Where the interests genuinely diverge, they diverge on extent. An owner’s interest in a marginal case is usually the larger scope; a contractor’s is usually the smaller one. This page does not resolve that, because it is an evidence question and the answer is on the roof. What it does say is that the argument goes better for whichever party sampled and documented, and that is nearly always the contractor, because the contractor was there first with the staging up.

There is one thing this page will not help with, and the boundary is not negotiable. It will not help characterise a workmanship defect as storm damage. Presenting an installation defect to an insurer as a dated loss is a misrepresentation, insurers and state regulators treat it as one, and where a licence or registration exists it is the fastest route to losing it — although requirements vary enormously by state and many states have no roofing-specific licence at all. See licensing, insurance and bonding. The rest of this catalogue is compatible with that boundary, which is the point: competent practitioners do not need the exception.

The one argument this page does make for the trade is a commercial one. Every defect above is cheaper to prevent than to find, and much cheaper to find at the tear-off than at the callback. That is not a moral claim. It is the arithmetic of sending a crew back — pricing and margin covers what a return trip actually costs once overhead recovery is counted.

Considerations

What changes this on a real buildingSection link

What moves these defects up or down the list on a particular building.

Climate: Freeze-thaw belts compress every water-management defect. A short head lap, a valley fastener or a missing kickout that would take a decade to produce a visible failure in a dry heat zone produces one in two or three winters where meltwater refreezes at the eave. See heavy snow and ice and ice dams. Salt-laden air does the same thing to the dissimilar-metal entry: coastal salt corrosion.
Code and jurisdiction: There is no nationwide building code for site-built construction. Every code-shaped statement on this page is model text from the International Residential Code, which is a document a government may adopt whole, adopt with amendments, or decline. What binds on a particular job is the edition that jurisdiction adopted, its amendments, its effective date, and what the authority having jurisdiction says.
MODEL TEXT. The IRC provisions cited here were read through a third-party code aggregator on 27 August 2026, because ICC's own Digital Codes site returns HTTP 403 to automated requests. That is a limitation of this page's verification, not a statement about the code. Confirm the wording against your adopted edition before relying on it.
Wind: Wind performance is site- and building-specific: exposure, height, geometry, pressure zone, enclosure, risk category and the tested assembly all matter. A marketing mph figure on a bundle wrapper is not a code determination for a building. What the fastener defects in this catalogue actually change is whether the roof achieves the attachment its own listing assumed.
Several products condition their wind warranty on the shingle having sealed. A shingle that never sealed because it was nailed high, or because it was laid in cold weather and never hand-sealed, is outside that condition before any wind arrives.
Moisture and ventilation: Vented and correctly designed unvented assemblies are both legitimate. The DOE Building America Solution Center describes both as code-recognised approaches and states that the key to an unvented roof is keeping the deck, as the principal condensing surface, warm enough year-round that condensation does not occur — in cold climates by holding air-impermeable insulation at 50 percent or more of the assembly’s total R-value. What is never right is a half-converted assembly: an unvented design with the soffits still open, or a vented design with the intake blocked.
There is no universal ventilation ratio. The ratio, the split between intake and exhaust, and whether ventilation is required at all depend on the adopted edition, the assembly, and the climate zone.
Fire: Fire classification belongs to a tested assembly — deck, underlayment and covering together — not to the covering alone. That matters here because two entries in the catalogue change the assembly: substituting an underlayment, or omitting one where the listing assumed it, can put the roof outside the assembly that was tested even though the visible covering is unchanged.
A Class A shingle is a shingle that has been tested in a Class A assembly. It does not carry the classification onto a different deck or a different underlayment by itself.
Maintenance: Two entries here are only defects because of what happened after handover. A pipe boot that has reached the end of its own life is a maintenance item, not an installation failure — unless it was already old when the covering went on, which is a scope decision. Debris in a valley, an intake vent insulated over during a retrofit, and a sealant repair that became the waterproofing all belong in this class.

Warranty and repair

What is covered, and what can actually be repairedSection link

The cause class is not an academic distinction. It is the whole of the warranty question.

What a material warranty covers: Manufacturing faults, broadly, and sometimes only where they produce a leak. CertainTeed’s applicator manual is direct about it: standard shingle warranties “tend to cover manufacturing defects,” and it advises contractors to “clarify the limits of their responsibility regarding their own workmanship and the shingle manufacturer’s warranty obligations” before starting a project. That sentence exists because the owner will not make the distinction for you.
What excludes it: Application that departs from the written instructions. The same manual lists, among a manufacturer’s exclusions, “defects, damage, or failure caused by application of its shingles not in strict adherence with CertainTeed’s written instructions.” IKO’s Cambridge application instructions put one specific case in capitals: “FOR ALL APPLICATIONS IT IS CRITICAL TO USE THE NAIL LINE AS A GUIDE. HIGH NAILING ABOVE THE NAIL LINE CAN VOID IKO’S LIMITED WARRANTY.” The same document opens by saying IKO assumes no responsibility for leaks or defects resulting from improperly installed shingles, improper preparation of the surface roofed over, or failure to provide proper ventilation.
The ventilation clause: Ventilation is the exclusion contractors most often discover after the fact, because it is not a roofing operation and it is frequently outside the scope that was priced. CertainTeed’s manual states that shingles applied to an inadequately ventilated or non-ventilated deck are “subject to a reduced limited warranty period of ten (10) years” and do not qualify for its non-prorated coverage. A twenty-five-year expectation becomes a ten-year one because of work nobody quoted.
Wind warranty: Usually shorter than the headline term, and usually conditional. The same manual notes that blow-off coverage “is shorter than the nominal warranty duration,” commonly five years, and that a very common limitation is a requirement that the shingle must have sealed. Two catalogue entries — high nailing and a missing starter course — attack that condition directly.
Workmanship warranty: A separate document from a separate party, covering the class the manufacturer excludes. Nothing in a manufacturer’s warranty answers for workmanship; nothing in a workmanship warranty answers for the mat. An owner holding both still has two gaps between them: design, and maintenance. See how roofing warranties are actually written.

Repairability

Repairability is a cause-class question too. A workmanship defect in the field — high nails through one elevation, say — is repairable in place only where the shingles will lift without tearing, which is a function of how long they have been sealed and how warm the day is. Past a certain age, lifting a course to correct a fastener destroys more than it fixes, and the honest answer becomes slope replacement.

Detail defects behave differently. A missing kickout can usually be added; the cost is in opening the cladding and re-lapping the drainage plane, not in the metal. A reused flashing generally cannot be corrected without taking the covering back off it, which is why the decision belongs in the estimate rather than in the callback. See flashing details and workmanship.

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.

Before anyone signs anything

Questions that close out a defect argumentSection link

Phrased so a contractor can ask them of a manufacturer's rep, an inspector can ask them of a contractor, and an adjuster can ask them of a file.

Which document are we calling the standard here — the code, the manufacturer's instructions, or a house practice?
These three disagree in places, and only two of them bind. A good answer names the document and the section. An answer that cites “industry standard” without a document is an answer that will not survive an argument.
What is the printed exposure and fastener count for this specific product, and where does the nail line sit?
Exposure and nail placement are product-specific and they move between products in the same manufacturer’s range. Anyone answering from memory across brands is describing a defect they have not noticed yet.
Are there deck photographs, and were they taken before the underlayment went down?
This single question decides more disputes than any technical one. Deck condition, existing flashing, layer count and ventilation openings are visible for about four hours per job and then never again.
Is the condition on every elevation, or only some — and which ones?
It is the fastest cut between weathering and everything else. Orientation-dependent points at UV and thermal load; orientation-blind and uniform points at material or design; clustered points at a crew, a day, or a detail.
Who did the ventilation, and was it in the roofing scope?
It is the most common gap between what a warranty assumes and what anyone priced. If nobody owns it, the manufacturer’s reduced-warranty clause may already be in effect and no one has noticed.
What date is the loss, and what does the condition look like relative to it?
A defect predates the storm; storm damage does not. Directional bias, fresh fracture surfaces, and a condition absent from sheltered elevations point one way; a uniform, weathered, everywhere condition points the other. Neither is proof on its own.

Put these in the file before the staging comes down

Deck photographs by elevation, dated, before any underlayment — including any existing flashing left in place and why.
A close-up of the fastener pattern on at least one shingle per elevation, showing head seating and position relative to the nail line.
The product name and the printed exposure, photographed on the wrapper rather than transcribed.
Photographs of every roof-to-wall termination showing the kickout, and of every valley showing the lining running through.
Intake and exhaust: what is open, what was blocked off, and what was left alone — with the reason.
The ice-barrier extent measured from inside the exterior wall line, where the jurisdiction requires one.
Any existing condition accepted rather than corrected, named in writing and initialled, before it becomes a callback about somebody's memory.

What goes wrong

What gets muddled, and how the investigation itself failsSection link

Common misconceptions

Common belief
A leak means the roof was installed badly.
What is actually true
It means water reached a place it should not have. That can be workmanship, a design fault the roofer inherited, a maintenance item nobody serviced, a genuine material fault, or a building that has simply run out of service life. Water also travels along framing before it appears, so the stain is evidence about the structure, not about the roof geometry — see water travel and how roof leaks behave.
Common belief
It is still under warranty, so the manufacturer will take care of it.
What is actually true
The manufacturer’s warranty addresses material — one of the four classes, and not the largest one. If the cause is workmanship, design or maintenance, or the covering has simply aged, the document does not reach it — and several clauses are written to reduce or exclude coverage where installation or ventilation departed from the instructions. Whoever explains this to the owner should be the person who read the actual warranty, not a summary of one.
Common belief
Six nails is always better than four.
What is actually true
Only if all six are in the right place. IKO’s Cambridge instructions call for six in high-wind areas and on slopes of 21:12 (60 degrees) or more — a far steeper threshold than the 4-in-12 that makes a roof “steep” under the OSHA definition quoted at the top of this page, so read the number off the instructions rather than off the word. They add that no nail should be within 2 inches of a joint or cutout in the underlying shingle. The model IRC requires the number the manufacturer’s approved instructions give, but not fewer than four per strip shingle. Two extra fasteners placed above the nail line add two more holes and no more holding.
Common belief
Granules in the gutter mean the shingles are defective.
What is actually true
Loose granules shed early — they are the excess from manufacture — and again at the end of service life as the asphalt embrittles and releases its grip. The diagnostic question is not whether granules are present but whether the shingle surface behind them is exposing mat, and whether the pattern is orientation-dependent. See granule loss.
Common belief
Caulk it and it is fixed.
What is actually true
Sealant is specified in specific places and quantities: hand sealing in cold weather, the ends of shingles at an open valley, exposed cap nail heads. It is not a substitute for geometry, and excess causes its own defect — both the CertainTeed and IKO documents warn that too much cement makes the shingle blister. Where sealant is the only thing between the water and the deck, that is a defect with a countdown on it.
Common belief
The inspector wrote 'high nails', so the whole roof has to come off.
What is actually true
Extent is the question, and the report should establish it. High nailing on one elevation installed by one person on one afternoon is a different problem from high nailing found in every test lift. A report that names a defect without sampling enough of the roof to describe its distribution has produced an observation, not a scope.

How it actually fails

The cause is determined from the ground: Every entry in this catalogue is either invisible from the ground or ambiguous from it. Binoculars and a drone establish that something is wrong; they do not establish which of five causes produced it, and a report that infers a cause from an aerial image is describing a guess in a professional register.What you can see: Reports whose cause statements are more specific than their observation statements.
The symptom gets repaired instead of the cause: A stain gets sealed, a boot gets caulked, a valley gets cemented. The symptom stops for a season and the mechanism keeps running, usually into the deck. The second failure is then both worse and harder to attribute, because a repair now sits between the investigator and the evidence.What you can see: Layers of sealant of different ages at one detail; a stain that moved rather than stopped.
The photographs are taken after the repair: Documentation is produced after the correction, so it records the fixed condition rather than the found one. Everyone afterwards is arguing from memory, and memory is not evidence.What you can see: A file whose earliest image already shows new material.
The extent is never sampled: A defect is named without a distribution, so it cannot be priced and cannot be defended. “High nailing observed” is not a finding; “high nailing observed in four of six test lifts on the south and west elevations, none on the north” is.What you can see: Scopes that jump straight from one observation to full replacement, or from one observation to no action.

Sources and further readingSection link

Understanding Roofing / Published August 27, 2026

Scope and limitations

It cannot tell you what caused the defect in front of you.
It sets out the classes, the mechanisms and the evidence that discriminates between them.
A destructive investigation, a laboratory evaluation of the material, or the manufacturer's own determination is what settles a contested cause.
It publishes no frequency data.
There is no public dataset apportioning roofing failures by cause, defect type, or trade, and the percentages that circulate for this — usually attributed to a trade association — have no traceable publication behind them.
The ordering of the catalogue is by mechanism, not by incidence.
It publishes no time-to-failure figures.
The 'what reveals it' column names an event rather than a number of years, deliberately, because no dataset supports a national service interval for any of these defects.
That includes penetration boots and sealant repairs, for which the industry repeats intervals nobody has published.
It publishes no cost figure.
Callback, repair and re-roof costs vary by market, access, extent and the age of the covering, and no defensible national dataset separates defect remediation from the rest of a roofing job.
Every code-shaped statement here is model text.
There is no nationwide building code for site-built construction; the reader's adopted edition, its amendments, its effective date and the authority having jurisdiction govern.
The model provisions cited were read through a third-party aggregator because ICC's own Digital Codes site returned HTTP 403 to automated requests on 27 August 2026 — an aggregator is not adopted law anywhere.
The manufacturer material is product-specific.
IKO's Cambridge instructions and CertainTeed's applicator manual are cited because they are published, readable and explicit; they bind those products and nothing else.
The instructions for the product actually on the roof control, and they change between products in one manufacturer's own range.
The cause-class assignments in the catalogue are this page's own analysis, not a sourced classification.
They describe where a defect usually originates, not where it originated on a particular building.
It makes no coverage, liability, licensing or classification determination, and it is not legal advice.
The warranty and claim sections have not had legal review; they describe how the documents cited are written, not what any warranty or policy will do.

Asphalt Shingle Roofs — resource guide
U.S. Department of Energy, Building America Solution Center (PNNL)
The named improper-nailing conditions ('high nails, low nails, overdriven nails, underdriven nails, angled nails, and inadequate nails'); do not use staples; starter strip position and its 1/4 to 3/4 inch overhang past the drip edge; the 2-in-12 minimum slope and the double underlayment requirement from 2-in-12 to 4-in-12; the ice-barrier extent to a point not less than 24 inches inside the interior plane of the exterior wall.
Guidance, not adopted law. Where it names code requirements it is summarising IRC editions it identifies; confirm against the edition your jurisdiction adopted.
Step and Kick-Out Flashing at Roof-Wall Intersections — resource guide
U.S. Department of Energy, Building America Solution Center (PNNL)
That kick-out flashing directs rainwater into gutters and away from the structure; that omission produces damage to wall sheathing, framing and insulation and mould in wall cavities, and that fibre-cement and vinyl cladding can conceal it for years; the code history (2009 and 2012 IRC R703.8; 2015 and 2018 IRC R703.4 and R903.2.1); step flashing extending at least 4 inches up the wall and 4 inches along the deck; metal flashing not less than 0.019 inch thick.
Cites the 2009, 2012, 2015 and 2018 IRC. None of those is necessarily the edition in force where the reader works.
Roof Valleys and Penetrations Sealed — resource guide
U.S. Department of Energy, Building America Solution Center (PNNL)
Valley and penetration membrane practice: self-sealing membrane installed directly on the sheathing beneath the underlayment, sections lapped 6 inches shingle-fashion, fasteners kept out of the 6 inches either side of the valley centre, at least 6 inches of membrane each side of and below a penetration, and the downslope-then-upslope sequence around a pipe.
Describes a sealed-deck best practice; the guide itself notes building codes generally do not require a sealed roof deck for new homes or roof replacements.
Roof Deck Sheathing and Sealing for Sloped Roofs — resource guide
U.S. Department of Energy, Building America Solution Center (PNNL)
Deck attachment practice: 8d ring-shank nails at 4 inches on centre within 4 feet of roof edges and either side of the ridge and 6 inches on centre elsewhere; minimum 7/16 inch plywood or OSB; and that sheathing nails which miss the trusses weaken the roof in high winds.
These are IBHS FORTIFIED programme requirements, not a code minimum. A deck fastened to code is not thereby defective.
Calculating Attic Passive Ventilation
U.S. Department of Energy, Building America Solution Center (PNNL)
That net free ventilating area is defined as the clear open area of a vent after its screening and slot dimensions are accounted for, that most screened vents have about 60 percent free area, that upper vents should be no more than 50 and no less than 40 percent of the required area, at least 3 feet above the lower vents and no more than 3 feet below the highest point of the roof, and the 1/300 and 1/150 ratios as the 2015 IRC R806.1 states them.
Cites the 2015 IRC. The ratio, the reduction conditions and whether ventilation is required at all depend on the adopted edition and the assembly.
Vented versus Unvented Attic — resource guide
U.S. Department of Energy, Building America Solution Center (PNNL)
That vented and unvented attics are both code-recognised approaches; that the key to an unvented roof assembly is keeping the roof deck, as the principal condensing surface, sufficiently warm year-round that condensation will not occur; and that in cold climates air-impermeable insulation should be maintained at 50 percent or more of the roof system's total R-value for condensation control.
Cites the 2012 IRC, a superseded model edition. Unvented assembly requirements have changed across editions and vary by climate zone.
29 CFR 1926.501 — Duty to have fall protection
U.S. Occupational Safety and Health Administration
The 6-foot trigger and permitted systems for steep roofs at 1926.501(b)(11), low-slope roofing work at 1926.501(b)(10), and residential construction at 1926.501(b)(13).
Federal OSHA. States operating their own OSHA-approved plans may have different or additional requirements, and applicability depends on the work and the employer. Nothing here is a compliance determination.
29 CFR 1926.500 — Scope, application, and definitions (Subpart M)
U.S. Occupational Safety and Health Administration
The definitions of steep roof (slope greater than 4 in 12), low-slope roof, roofing work and unprotected sides and edges at 1926.500(b), and the scope statement at 1926.500(a) excluding inspection, investigation or assessment of workplace conditions before construction starts or after it is complete.
Definitions and scope for Subpart M only. The inspection-and-assessment exclusion is a statement about which standard applies, not an assurance that any particular activity is safe or unregulated.
Fall Protection in Residential Construction — compliance guidance
U.S. Occupational Safety and Health Administration
That STD 03-11-002 rescinded the interim residential fall-protection compliance guidelines, and that an employer demonstrating infeasibility or greater hazard must instead implement a written fall protection plan meeting 1926.502(k).
Agency guidance, not the standard text itself. The page carries no publication date.
Master Craftsman Shingle Applicator's Manual, Sixteenth Edition
CertainTeed / Sixteenth edition, © 03/23, Code No. 13-03-1741-NA-EN
The 'common workmanship defects' framing and its list — over- and under-driven nails and their relation to air-gun pressure in cold weather, fasteners driven outside the approved pattern by the arc of the gun, missing fasteners under vertical racking, and short fasteners backing out; 'High nailing: prohibited'; the position that nails are preferred to staples; nail specification (11 or 12 gauge, 3/8 inch head, 3/4 inch penetration or through a thinner deck); the instruction to seal an overdriven nail and set another beside it; the galvanic scale and the instruction to use fasteners of the same metal as the flashing and to isolate unavoidable pairs with underlayment, bituminous paint or another non-conducting material; the ventilation balance rule that effective ventilation is limited to the lesser of intake and exhaust; 'never mix two types of exhaust vents'; blocked intake openings; the reduced ten-year warranty on inadequately ventilated decks; that standard shingle warranties tend to cover manufacturing defects and exclude application not in strict adherence with the written instructions; that wind coverage is shorter than the nominal term and commonly conditioned on the shingle having sealed; that excess roofing cement causes blistering; the APA 1/8 inch panel gap; wide board decking as a cause of shingle buckling; and two 8d nails per board at each rafter.
One manufacturer's training manual. Product-specific and commercially interested; it is not code and it does not bind another manufacturer's products. Read as full extracted text, not as a summary.
IKO Cambridge Shingles — Application Instructions
IKO / © 01/21, documents 342261 / 342263 / 342308
'IT IS CRITICAL TO USE THE NAIL LINE AS A GUIDE. HIGH NAILING ABOVE THE NAIL LINE CAN VOID IKO'S LIMITED WARRANTY'; the Overdriven / Crooked / Underdriven / Perfectly Nailed diagram; the 5-7/8 inch exposure for this product and the 6 to 10 inch offset range; starter shingles required at all eaves and rakes with a 1/4 to 3/4 inch overhang for high-wind warranty coverage; four nails standard and six on slopes of 21:12 or more and in high-wind areas, with no nail within 2 inches of an underlying joint or cutout; fasteners 11 or 12 gauge with 3/8 inch heads penetrating 3/4 inch into the deck or 1/8 inch through a thinner one; the open metal valley method including the 36 inch membrane, the minimum 24 inch wide 28 gauge liner, chalk lines 6 inches apart widening 1/8 inch per foot, and no nail closer than 2 inches to the chalk line; never applying shingles below 2:12 and the twelve-year warranty limit between 2:12 and 3:12; minimum 3/8 inch plywood or 7/16 inch non-veneer decking with board decks not recommended; the caution that excessive roofing cement can cause blistering; and 'IKO assumes no responsibility for leaks or defects resulting from improperly installed shingles.'
Product-specific instructions for IKO Cambridge shingles. They do not describe any other product, and IKO's own range differs internally. Read as full extracted text.
TruDefinition Duration Shingles — product brochure with printed specifications table
Owens Corning Roofing and Asphalt, LLC / Pub. No. 10013978-B, May 2012
The published product specification used in the worked exposure calculation: nominal size 13-1/4 by 39-3/8 inches, exposure 5-5/8 inches, 64 shingles and 3 bundles per square, coverage 98.4 square feet per square.
A 2012 consumer marketing brochure that carries a printed 'Product Specifications' table, used here only for the nominal dimensions and coverage that the exposure arithmetic reproduces. It is not current product data; read the current data sheet for the product actually being installed.
2024 International Residential Code, Chapter 9: Roof Assemblies
International Code Council (model text), read through UpCodes / 2024 International Residential Code (model), read in a GSA adoption viewer
MODEL wording of R903.2 (flashings installed at wall and roof intersections, wherever there is a change in roof slope or direction, and around roof openings); R905.2.5 (fastener specification); R905.2.6 (the number of fasteners the manufacturer's approved instructions require, but not less than four per strip shingle); R905.2.2 (asphalt shingles only on slopes of 2 in 12 or greater); R905.2.8.5 (drip edge not less than 1/4 inch below the sheathing and not less than 2 inches up the deck); and R905.1.2 (ice barrier where Table R301.2 designates a history of ice forming at the eaves, extending to a point not less than 24 inches inside the exterior wall line).
An aggregator is never adopted law. This is MODEL text; the ICC Digital Codes site returned HTTP 403 to automated requests on the access date, so the official publication was not read. Confirm against the edition and amendments adopted where the work is.
Reroofing by the book — Mark S. Graham
National Roofing Contractors Association, Professional Roofing / February 2019
The recover-versus-replacement distinction, the two-layer limit and the prohibition on recovering a water-soaked or deteriorated roof under IBC 2018 Section 1511, and the Section 1511.5 provision that existing vent flashings, roof edge metal, metal counterflashings, drain outlets and collars are not to be reinstalled where rusted, damaged or otherwise deteriorated.
A 2019 article about the 2018 International Building Code — a commercial model code, superseded editions of which now exist, and not the residential provision. It is not adopted law anywhere. Cited only for the reroofing framing the catalogue's 'reused or omitted flashing' entry relies on.

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