Roof Pitch Standards

Codes

• Local and state building authorities across the U.S. regulate the construction of a house and its roof, by copying rules either directly or with modifications from the International Residential Code. The International Code Council, a non-profit founded in 1994, manages this code and others such as the International Fire Code and International Energy Conservation Code, which can all affect roof pitch standards. The mission of this organization is “to provide the highest quality codes, standards, products and services for all concerned with the safety and performance of the built environment.”

Calculations

• Pitch, also known as slope or grade, is the ratio of a roof’s rise against its forward movement in 12 units. For example, a structure that rises 3 inches for every 12 inches has a pitch of 3:12. A low-pitch roof has a ratio of 5:12 or less. This makes it the easiest and least expensive to install and maintain. More expensive is a medium-pitch roof, with ratios of 6:12 to 9:12 because it requires planks and roofing jacks for installation. A high-pitch roof, ranging from 10:12 to 12:12 -- a 45-degree angle -- is the most difficult and expensive installation. It requires special protections and fall arrest equipment.

Standards

• Though roofs can use any maximum pitch, limited only by design and budget, the minimum ratio is defined in building codes and depends on material. Asphalt shingles, frequently used because they are cheap and durable, needs a minimum pitch of 2:12, and double underlayment for pitches up to 4:12. Clay and concrete tile, which are naturally fireproof and impervious to insects, require a minimum slope of 2.5:12, with ratios up to 4:12 also requiring double underlayment. For metal shingles, which can duplicate natural textures, the smallest ratio is 3:12. But for metal panels, which add a modern touch, pitch can range from 0.25:12 for systems up to 3:12 for those with lapped, nonsoldered seams without applied lap sealant.

Nature

• Natural materials such as wood shingle or shake remain desirable because of their texture and breathability, and because they can be stained with different colors, and cut to different designs. They need a minimum pitch of 3:12. Slate tile is long-lasting and architecturally dimensional, but also one of the most expensive materials. It needs a slope of 4:12 or greater.