Roof Pitch Regulations

IRC

• Local building authorities must approve roof installations to certify their usability by homeowners. To win this nod, contractors must follow local, state or some federal regulations. Though thousands of jurisdictions implement and develop roofing rules, they base their regulations on the International Residential Code, or IRC, managed by the International Code Council. The mission of this nonprofit organization is to ensure the consistency of safe construction in any location in the U.S. The council also manages related codes such as the International Building Code and the International Fire Code.

Pitch

• Pitch, which is also called slope or grade, measures the way a roof slope angles from the horizontal. It is expressed as the number of inches a roof rises over every 12 inches of forward movement. Low-pitched roofs, such as those measuring 3:12 or lower, are cheaper to install and can be walked on with no additional equipment. Steep roofs, such as those measuring 10:12 to the maximum 12:12 (45-degree angle) are more expensive to install and maintain because they are not walkable. They also require safety equipment such as fall arrestors for the roofers.

Regulations

• The IRC specifies minimum roofing slope based on the material used to cover the roof. For instance, asphalt shingles are the most common roofing choice in the U.S. They need a roofing deck slope measuring 2:12 or greater. However, roofs ranging from 2:12 to 4:12 require double underlayment. Clay and concrete tiles, which are naturally impervious to fire and may grant insurance discounts, need a minimum 2.5:12. Slopes up to 4:12 also need double underlayment. Natural and artificial slate shingles need a slope of 4:12 or greater.

Other Roofing Material

• Wood shingles, which are valued for their natural beauty, need a minimum slope of 3:12. Wood shakes, which are thicker than shingles and have only one finished side, need a 3:12 slope or greater; metal shingles also need the same ratio. Non-soldered metal seam roofs without applied sealant must measure 3:12 or more. The same type of roof with applied sealant can go on roofs measuring 0.5:12 or more. A standing-seam roof has the lowest slope allowable by the IRC for roof. It must have a minimum slope of 0.25:12.