The short answer
GAF is the volume leader in this market. Its impact-rated Timberline AS II carries a UL 2218 Class 4 rating, uses SBS-modified asphalt, and is rated ASTM D3161 Class F and ASTM D7158 Class H for wind. The detail most homeowners miss: GAF states plainly that its shingles are not warranted against hail damage, whatever the impact class.
Verified specifications
| Item | What GAF publishes |
|---|---|
| Timberline AS II | UL 2218 Class 4, SBS-modified asphalt |
| Wind rating | ASTM D3161 Class F and ASTM D7158 Class H |
| WindProven warranty | 15 years with no maximum wind speed, when installed with four required GAF accessories: starter strip, roof deck protection, ridge cap, and a leak barrier or attic ventilation |
| Algae warranty | 25-year StainGuard Plus on qualifying packages |
| Defect warranty | Lifetime limited for original owners of single-family detached homes |
| Hail | Not warranted against hail damage, per GAF |
Figures above come from GAF published product and warranty documents. Specifications change, so confirm against the current data sheet for the exact product before you sign a contract.
What this means for a roof here
Impact class earns an insurance credit, and in the Hill Country that credit compounds every year you own the house. What it does not do is make a roof hail proof. Manufacturers generally do not warrant shingles against hail damage, and a 2025 study by the Insurance Institute for Business and Home Safety found impact-resistant shingles performed only slightly better than conventional shingles against cumulative granule loss from repeated small hail. Buy the class for the insurance credit and the margin against large stones, not for immunity.
The other thing worth noticing across every brand on this page is how often the headline rating depends on the system rather than the shingle. Wind ratings and warranty tiers routinely require that manufacturer's starter, underlayment and ridge cap. A shingle installed without its specified components does not carry its advertised performance, and that gap is where cheap bids come from.
