The IRC on wind, ice and hail, section by section

R301.2: the numbers your jurisdiction fills in

Section R301.2 says additional climatic and geographic criteria are established by the local jurisdiction and set forth in Table R301.2. That table has columns for wind design, covering speed, topographic effects, special wind regions and windborne debris zones, plus a column for whether ice barrier underlayment is required. Ask the building department for its completed table, because it drives everything below.

R301.2.1: wind design criteria

Section R301.2.1 builds wind design on the ultimate design wind speed, Vult, from Figure R301.2(2). Where nothing else is specified, roof coverings must meet the component and cladding loads in Table R301.2.1(1), adjusted for height and exposure with Table R301.2.1(2). The same section sends asphalt shingles to Section R905.2.4 and metal roof shingles to R905.4.4, and requires a continuous load path for uplift from the roof assembly to the foundation.

When the IRC hands off to engineered design

Under R301.2.1.1, the IRC's own wind provisions stop applying where Figure R301.2.1.1 requires wind design, or where Vult reaches 140 mph or more in a special wind region. There, the house is designed with the AWC Wood Frame Construction Manual, ICC 600, ASCE 7, AISI S230 or the International Building Code.

Exposure and speed conversion

Section R301.2.1.4 assigns each site Exposure B, C or D. B is the default for urban, suburban and wooded terrain; C covers open terrain with scattered obstructions; D covers flat ground exposed to wind over open water, mud flats or salt flats for at least 5,000 feet. Where a product standard uses nominal speeds, Table R301.2.1.3 converts them: a Vult of 140 mph corresponds to a Vasd of 108 mph, for example.

Hurricane-prone regions and debris

Chapter 2 of the 2024 IRC defines hurricane-prone regions as the U.S. Atlantic and Gulf of Mexico coasts where Vult exceeds 115 mph, plus Hawaii, Puerto Rico, Guam, the Virgin Islands and American Samoa. Its windborne debris regions sit inside those areas: within 1 mile of the mean high-water line where Exposure D and speeds of 130 mph or more combine, or wherever Vult is 140 mph or higher. Glazing in a debris region must meet the large missile test of ASTM E1886 and ASTM E1996 or use the wood structural panel exception.

R905.2: asphalt shingles

Section R905.2.1 requires shingles to be fastened to wood structural panels or solid lumber sheathing. Under R905.2.2 they may go only on slopes of 2:12 or steeper, with double underlayment from 2:12 up to 4:12, and R905.2.4 requires them to comply with ASTM D3462.

R905.2.4.1: wind classification

Section R905.2.4.1 requires shingles to be tested to ASTM D7158, with the packaging labeled for the class Table R905.2.4.1 assigns to the design wind speed. Shingles outside the scope of D7158 are tested and labeled to ASTM D3161 instead.

In summary, the table accepts D7158 Classes D, G or H at its lowest listed speeds, requires G or H from 129 mph and Class H from 168 mph; on the D3161 side, Class F is the only option from 142 mph up. A footnote says D7158's standard calculations assume Exposure B or C and a building no taller than 60 feet. Read the full table on ICC's page before you order shingles.

Fasteners and nailing

Roofing nails must be galvanized steel, stainless steel, aluminum or copper, at least 12-gage with a 3/8-inch head, compliant with ASTM F1667, and long enough to reach 3/4 inch into the sheathing or pass through it. Section R905.2.6 sets a floor of four fasteners per strip shingle or two per individual shingle, or more where the manufacturer's instructions call for it.

R905.1.2: ice barriers

Where Table R301.2 records a history of ice forming along the eaves and backing up water, R905.1.2 requires an ice barrier under asphalt shingles, metal roof shingles, mineral-surfaced roll roofing, slate and wood shingles and shakes. It is either two layers of underlayment cemented together or a self-adhering polymer-modified bitumen sheet, running from the lowest roof edge to at least 24 inches inside the exterior wall line.

On slopes of 8:12 or steeper, the barrier runs at least 36 inches along the slope from the eave, and detached accessory structures without conditioned floor area are exempt. When a roof is replaced, Section R908.3 can let an existing adhered ice barrier membrane stay in place if the sheathing beneath it is not water soaked or deteriorated.

Hail: what the codes say, and don't

A search of the full text of chapters 3 and 9 of the 2024 IRC finds no hail-resistance rating for residential roof coverings; the shingle tables rate wind only. The 2024 IBC's Section 1504.7 requires low-slope coverings to resist impact damage under ASTM D3746, ASTM D4272 or FM 4470, which is an impact rule for flat roofs rather than a hail rating.

Florida's HVHZ test protocols do contain a hail test by title, TAS 114 Appendix F, covered in the Florida HVHZ guide. For houses elsewhere, hail ratings usually arrive through products and programs: IBHS's FORTIFIED Hail Supplement, for example, requires UL 2218 Class 4 metal panels or FM 4473 Class 4 tile. See the FORTIFIED guide and NRD's explainer on Class 4 impact-resistant shingles.

For roofers keeping current

Roofers who want code and storm updates can subscribe to The Roofing Wire, the National Roofing Directory's free weekly issue, and can claim a listing on the directory. NRD's membership levels run Claimed, Verified, Gold and Platinum.

Frequently asked questions

Does the IRC require Class 4 impact-resistant shingles?

Not in the 2024 edition's roof chapter, which classifies shingles for wind, not hail. Grant programs can ask for more: Oklahoma's requires the FORTIFIED Hail Supplement, for instance.

What do Class F and Class H on a shingle bundle mean?

They are wind classes from two test standards, Class F under ASTM D3161 and Class H under ASTM D7158, and they are the top classes in Table R905.2.4.1. FORTIFIED Roof requires one or the other.

Is an ice barrier required on every roof?

No. It applies where the jurisdiction's Table R301.2 designates a history of ice forming along the eaves.