The Proper Slope for the Roof

Climate Considerations

• In areas that receive a lot of snow, roof slopes tend to be steeper, to encourage heavy snowfall to slide off the roof. If you live in such a region, check with your local building authority about roof pitch requirements for snow load. Warm and dry climates are more suited to lower-pitch roofs, and in some Southwestern states, flat roofs are the norm. Even flat roofs, however, have some slope in order to allow drainage off the roof or into a drain installed on the roof. The slope is so slight that in many cases it might not be noticeable.

Slope and Roofing Materials

• Shingle manufacturers may require a minimum slope when installing their product. Typically, a 4:12 slope, or higher, is adequate for installing asphalt shingles. Roof slope ratios indicate the amount of rise per lineal foot. A roof with a 4:12 pitch rises vertically 4 inches for every 12 inches of roof width. Some shingle manufacturers may not warrant their product if it’s installed on a roof with a pitch less than 3:12. Roofing contractors often recommend a rolled-type rubberized roofing for roofs with a pitch less than 2:12.

Slope and Roof Construction

• Roof rafters are the traditional material for stick-framing roofs. In general, the lower the slope of the roof; the larger the rafters must be to support its weight. Roof trusses, however, which are preengineered at a truss manufacturing company, contain smaller members. Trusses use a system of triangles to support the roof. If you’re building a new house and you want a different slope on the roof than the blueprints call for, it’s likely that roof trusses can be designed to suit the slope you would like.

Codes and Covenants

• Often the proper slope of the roof depends upon the roof slope on neighboring homes. Consistency of design and style are considerations in new subdivisions and established neighborhoods. You probably won’t be able to build a house with a 2:12 roof pitch in a neighborhood where the homes all have a 6:12 pitch. In addition to the slope of the roof, you may be required to install a specific type of roofing material that blends in with the neighboring homes.