Slope Minimum for Various Roof Coverings

We just updated InterNACHI’s article on how to measure roof slope with the following information:

The International Residential Code (IRC) specifies minimum requirements for roof coverings and mandates the use of the roof-covering manufacturer’s installation instructions.

[ul]
[li]Asphalt shingles should be installed on roof slopes 2:12 or greater (2015 IRC R905.2.2).[/li][li]Clay and concrete roof tiles should be installed on roof slopes 2.5:12 or greater (2015 IRC R905.3.2).[/li][li]Metal roof shingles should be installed on roof slopes 3:12 or greater (2015 IRC R905.4.2).[/li][li]Mineral-surfaced roll roofing should be installed on roof slopes 1:12 or greater (2015 IRC R905.4.2).[/li][li]Slate shingles should be installed on roof slopes 4:12 or greater (2015 IRC R905.6.2).[/li][li]Wood shingles should be installed on roof slopes 3:12 or greater (2015 IRC R905.7.2).[/li][li]Wood shakes should be installed on roof slopes 3:12 or greater (2015 IRC R905.8.2).[/li][li]Built-up roofs should be installed on roof slopes 0.25:12 or greater (2015 IRC R905.9.1), except for coal-tar built-up roofs that have a minimum roof slope of one-eighth unit vertical in 12 units horizontal (1% slope).[/li][li]Metal roof panels should be installed on roof slopes according to particular seams (2015 IRC R905.10.2):[/li][LIST]
[li] minimum roof slope of 3:12 for lapped, nonsoldered-seam metal roofs without lap sealant applied[/li][li]minimum roof slope of 0.5:12 for lapped, nonsoldered-seam metal roofs with lap sealant applied[/li][li] minimum roof slope of 0.25:12 for standing-seam roof systems[/li][/ul]

[li]Modified bitumen roofing should be installed on roof slopes 0.25:12 or greater (2015 IRC R905.11.1).[/li][li]Thermoset single-ply roofing should be installed on roof slopes 0.25:12 or greater (2015 IRC R905.12.1).[/li][li]Thermoplastic single-play roofing should be installed on roof slopes 0.25:12 or greater (2015 IRC R905.13.1).[/li][li]Sprayed polyurethane foam roofing should be installed on roof slopes 0.25:12 or greater (2015 IRC R905.14.1).[/li][li]Liquid-applied roofing should be installed on roof slopes 0.25:12 or greater (2015 IRC R905.15.1).[/li][li]Photovoltaic shingles should be installed on roof slopes 2:12 or greater (2015 IRC R905.16.2).[/li][/LIST]
If you’re interested in access the IRC books, visit https://codes.iccsafe.org/public/collections/I-Codes

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