International Residential Code (IRC) Chapter 9

The International Residential Code (IRC) is a model code published by the International Code Council (ICC) for detached one- and two-family dwellings and townhouses. It sits alongside the International Building Code, which covers other buildings. Like the IBC, it is updated every three years and is adopted, often with local amendments, by most US states and many municipalities.

The IRC is written in a prescriptive style so that builders can follow it without engineering design in most cases.

Chapter 9: Roof Assemblies

Chapter 9 of the 2024 IRC includes sections on:

• general requirements
• fire classification
• weather protection (flashing, crickets, drainage)
• materials
• requirements for roof coverings (Section R905)
• roof insulation
• rooftop photovoltaic systems
• reroofing

Section R905 is the part roofers use most. It sets rules for each roof covering type, including:

• Asphalt shingles – minimum slope, underlayment, fastening, ice barrier requirements in cold climates, flashing details and wind classification under ASTM D7158 or ASTM D3161 depending on design wind speed.
• Clay and concrete tile, metal roof shingles and panels, slate, wood shingles and shakes – minimum slopes, underlayment and attachment.
• Low-slope coverings – built-up, modified bitumen, single-ply, sprayed foam and liquid-applied systems.

Referenced product standards include ASTM D3462 for asphalt shingles and UL 2218 where impact resistance is claimed.

Other relevant chapters

Roof framing, sheathing and ventilation of attics and enclosed rafter spaces are in Chapter 8 (Roof-Ceiling Construction). Energy efficiency, including roof and ceiling insulation, is in Chapter 11, based on the International Energy Conservation Code.

Regional differences

Local amendments are common in roofing, for example:

• extra wind provisions in hurricane-prone coastal areas
• requirements for ice barrier underlayment in snow regions
• Class A roofs in wildland-urban interface areas

Homeowners and contractors should confirm the edition and amendments adopted locally before planning a roof replacement.