What a composition shingle is, and what its rating means
A modern composition shingle is a fibreglass mat saturated and coated with asphalt, surfaced with mineral granules that shield the asphalt from ultraviolet light, and fitted with a factory-applied thermoplastic sealant strip that bonds each course to the one above once the roof gets warm. Four standards describe it, and confusing them is how most bad roofing conversations start.
- ASTM D3018 classifies by type: Type I is self-sealing, Type II is not.
- ASTM D3161 is a fan-induced wind test. Classes A, D and F correspond to 60, 90 and 110 mph.
- ASTM D7158 is an uplift force and uplift resistance method for self-sealing shingles. Classes D, G and H correspond to basic wind speeds of 115, 150 and 190 mph.
- UL 2218 rates impact resistance by dropping a steel ball. Classes 1 to 4 correspond to 3.53, 7.35, 13.56 and 23.71 foot-pounds.
The two wind scales are not interchangeable. The building codes require asphalt shingles with factory-applied self-sealing strips to be classified for wind resistance using ASTM D7158. When a salesperson quotes a D3161 Class F figure of 110 mph against a competitor's D7158 Class H at 190, those are two different tests on two different scales. The comparison is meaningless.
And the rating is conditional on the installation. A wind class assumes the manufacturer's fastening pattern, the specified number of nails, correct placement, and — critically — that the sealant strip has actually sealed. An unsealed or badly nailed shingle does not carry its rated wind resistance regardless of the wrapper.
Sealant strip failure — the central North Texas failure mode
The bond between the sealant strip and the tab above is what resists wind uplift. Nothing else on the surface of the roof does that job. When the bond goes, the shingle is a loose flap held by four nails at its top edge, and it will crease, lift or leave.
Why it fails here, roughly in order of regional relevance:
- Installed cold and never sealed. The strip is a thermoplastic adhesive requiring roof-surface heat to bond. A roof installed in December may not reach sealing temperature until spring, and if it is windy in the meantime the tabs lift, the strip picks up dust, and it never bonds at all. In a market where hail drives re-roofing year-round, this is a real regional failure mode rather than a theoretical one.
- Thermal cycling. Over years of North Texas surface temperatures and large day-to-night swings, the asphalt in both the mat and the sealant oxidises and loses plasticity. The bond becomes brittle and releases.
- Someone broke the seal. Anyone walking the roof, and anyone lifting tabs to inspect, breaks seals — and on an aged roof they may never re-bond. That is a real cost of the storm-chasing inspection culture here.
In a report it appears as tabs that lift by hand under light pressure; wind creasing, a horizontal crease where a tab folded back and laid down again; missing tabs; shingles displaced but still nailed. The distribution is diagnostic — these cluster on windward slopes, at the rake edges, and at ridges and hips, where uplift pressures are highest. Scattered lifted tabs in a field are one finding. Wind creasing along an entire rake is another.
Fasteners, and the defect an inspection cannot find
The code sets a floor and defers to the manufacturer. IRC R905.2.6 requires the manufacturer's minimum number of fasteners, but not less than four per strip shingle or two per individual shingle. R905.2.5 requires corrosion-resistant roofing nails, minimum 12 gauge with a 3/8-inch head, penetrating at least 3/4 inch into the sheathing.
The manufacturers are more specific, and their instructions are the controlling authority. ARMA directs installers to place nails below the sealant strip but above the area that will be visible after the roof is complete, requires a minimum of four nails per full-size strip shingle for most products, and states plainly that nails improperly located or driven can lead to sealing failures, blow-offs, raised tabs, and buckling.
The failure modes are all versions of the nail being in the wrong place or set wrong:
- High nailing. Nails above the specified zone miss the top edge of the course below entirely. Each shingle is then held by a single thickness, the head sits exposed in the weather lap, and the tab below is unsecured. High-nailed roofs shed tabs far below the shingle's rated wind speed.
- Nails in the exposure, overdriven, underdriven, or driven at an angle. An exposed head is a leak path; a head crushed through the mat has no holding power; a proud head wears a hole in the shingle above; and a shiner that missed the deck is visible from the attic as a nail protruding at an odd angle.
Now the uncomfortable part. High nailing is invisible from the ground, invisible from a drone, and largely invisible from the roof surface without lifting shingles — which an inspector is not required to do and which risks the very damage the Standards permit an inspector to avoid. It is one of the most consequential defects a home inspection cannot reliably find. (ARMA, Nail Application of Asphalt Strip Shingles.)
Thermal ageing, and what is simply normal
Asphalt shingle ageing is oxidation, accelerated by temperature and ultraviolet light. The governing variable is roof surface temperature, not air temperature, and a dark shingle on a sunny North Texas afternoon runs far above ambient. Over cycles the volatile oils migrate out, the asphalt embrittles, granules lose their grip in a coating repeatedly softened and re-hardened, and the sealant bond degrades.
The end-of-life indicators appear in a rough sequence, and knowing the sequence tells you where a roof sits: granule thinning uniformly across sun-exposed slopes with granules accumulating in gutters; loss of flexibility, so a shingle cracks rather than bends when lifted; curling and cupping at tab corners; exposed black asphalt, then fibreglass mat showing through; craze cracking across the surface; and finally loss of the sealant bond and wind loss of tabs.
Now the part a reference site owes you and a contractor will not offer. In North Texas, south- and west-facing slopes age faster than north-facing slopes on the same roof, and that is normal. A report noting materially different condition on different slopes of one roof is describing ordinary thermal ageing with a directional signature — not a defect, and not a workmanship failure. If someone points at a weathered west slope and a clean north slope as evidence that something went wrong, they have described the sun.
The warranty is not a service life
The number on the wrapper — 30-year, 50-year, Lifetime — is a warranty term, not a prediction of how long the roof will last, and reading the actual documents makes that unmistakable.
It covers manufacturing defects, not weather. GAF's Silver Pledge limited warranty excludes acts of nature such as hail, fire, or winds including gusts over the applicable listed wind speed. The two things that actually destroy Dallas-Fort Worth roofs are excluded by name.
Ventilation is a condition of coverage, and both major manufacturers say so in writing. GAF: failure to install adequate ventilation is not an application error of GAF products and is not covered under the limited warranty. CertainTeed: shingle damage or failure resulting from inadequate ventilation is not covered by CertainTeed's limited shingle warranty. That makes an attic ventilation deficiency a financial finding rather than a comfort one, and it is the strongest argument for fixing soffit intake at the next re-roof, when it is cheapest.
Transfer is limited and time-boxed. GAF's Silver Pledge may be transferred only once, and the second owner must notify GAF in writing within one year after the property transfer. A buyer who wants the seller's shingle warranty has to do something, on a deadline, and almost nobody does. Terms differ by product, so read the specific document.
Which leaves the question everyone asks. We will not publish a number. There is no primary research on asphalt shingle service life in a hot, high-ultraviolet Texas climate that we can stand behind, and every figure in circulation traces to warranty terms or marketing. The regionally honest answer is better anyway: the practical determinant of a roof's life here is usually the next hail event, not oxidation. Note too that the Standards do not require an inspector to determine remaining life expectancy — so a figure offered in a report is a courtesy opinion, not a finding. (GAF Silver Pledge Limited Warranty.)
What an inspector can and cannot determine
Required to report: the type of roof covering; the vantage point from which the roof was inspected; evidence of water penetration; and evidence of previous repairs to the covering, flashing details, skylights and other penetrations. The inspector must report as deficient any deficiencies in fasteners, adhesion, roof covering materials, flashing details, skylights and other roof penetrations. Adhesion is named explicitly — the sealant bond is inside the scope.
Not required to: inspect from roof level where the inspector cannot safely reach or stay on the roof, or where walking it may cause significant damage; determine remaining life expectancy or the number of layers; identify latent hail damage; exhaustively examine fasteners and adhesion; or provide an exhaustive list of deficiencies.
Read that pair together and the shape of a roof section becomes clear. An inspector tells you the covering type, where they stood, and what they found deficient. An inspector does not tell you how many years are left, does not lift shingles across the roof to audit the nailing, and is not warranting that every unsealed tab in an acre of shingles was found. Those are written limits, not gaps in diligence, and an inspector who ignores them is trading accuracy for the appearance of thoroughness.
What to do about it
Separate ageing from failure. Uniform granule loss with mild curling on a mid-life roof, no leaks, no wind creasing, is a monitoring item and an insurability question — not a repair.
Treat unsealed tabs by their distribution. A few isolated lifted tabs on an otherwise sound roof is a targeted repair, with the honest caveat that a roof which has started releasing seals will release more in the next wind event. Widespread unsealed tabs and wind creasing across multiple slopes is a different scale of finding and belongs with a roofing contractor before closing.
If the roof is new and already misbehaving, suspect the install. Lifting tabs, buckling or blow-offs on a young roof point at nailing or sealing rather than at age. That needs a roofer who will lift shingles, because the inspection cannot confirm it.
Do the ventilation work at the re-roof. Both manufacturers quoted above exclude ventilation-related shingle failure. Correcting soffit intake and exhaust is cheapest when the roof is off, and doing it then converts an argument you would lose into a warranty you might keep.
Common questions
What does a 30-year shingle actually guarantee?
A prorated remedy against manufacturing defects, and very little else. GAF's Silver Pledge warranty calculates the amount of use by dividing months elapsed by months in the term, and excludes acts of nature such as hail and winds over the applicable listed speed — the two causes that actually replace roofs in North Texas. Both GAF and CertainTeed also exclude damage resulting from inadequate ventilation. The term on the wrapper is a warranty period, not an expected service life.
My shingles are rated 110 mph but my neighbour's say 130. Whose roof is stronger?
You cannot tell from those numbers, because they are probably from different tests. ASTM D3161 is a fan-induced test with classes A, D and F at 60, 90 and 110 mph. ASTM D7158 is an uplift resistance method for self-sealing shingles with classes D, G and H at basic wind speeds of 115, 150 and 190 mph, and it is the test the building codes reference for modern self-sealing shingles. Either way, the rating assumes the manufacturer's nailing pattern and that the sealant strip has sealed.
Why are tabs lifting on a roof that is only a few years old?
Most often the sealant strip never bonded. It is a thermoplastic adhesive that needs roof-surface heat, so a roof installed in cold weather may not seal until spring — and if it is windy in the meantime, tabs lift, the strip contaminates with dust, and it never bonds. Improper nail placement produces the same symptom: ARMA states that nails improperly located or driven lead to sealing failures, raised tabs, blow-offs and buckling. On a young roof this is a workmanship question for the installer, not a wear item.
Is it normal for one side of my roof to look much worse than the other?
In North Texas, yes. South- and west-facing slopes take far more solar load and age faster than north-facing slopes on the same roof, so a directional difference in granule cover, colour and flexibility is the expected pattern of ordinary thermal ageing. What would be unusual is damage concentrated on a slope with no directional logic, or heavy granule loss on the north slope while the west slope looks new. Those patterns deserve a second look.
Can an inspector tell me if the roof was nailed correctly?
Generally no, and this is the most consequential thing a home inspection cannot confirm. High nailing — fasteners placed above the manufacturer's zone so they miss the course below — is invisible from the ground, from a drone, and from the roof surface without lifting shingles. The Standards do not require exhaustive examination of fasteners and adhesion, and they permit an inspector to avoid actions that may significantly damage the covering. Confirming nailing requires a roofer lifting shingles.
Should I replace a roof that is losing granules but not leaking?
Not on granule loss alone. Uniform granule thinning across sun-exposed slopes is ordinary oxidation, and Haag's testing found that granule loss without a fracture of the reinforcement did not affect service life. The signals that actually indicate end of life are loss of flexibility, curling, exposed mat, craze cracking and loss of the sealant bond. In the meantime, confirm what a carrier will charge to insure the roof at its current age — in this market that often drives the timing more than the shingles do.