What Is the Minimum Pitch for a Tiled Roof?

Pitch

• The pitch, also known as slope or grade, is the way in which the roof angles from the horizontal toward its highest point. A high-pitched roof shows the greatest surface to the street and is associated with traditional structures. But it is more difficult and expensive to install. A low-pitched roof is easier to put up and maintain, but may show very little of its material at ground level. To calculate roof pitch, take the lowest point of the roof and measure the amount of rise for every 12 inches of horizontal movement toward the highest point. For example, a roof that rises 3 inches for every 12 inches has a pitch of 3:12.

Standards

• Roofers must turn to local or state building codes when installing tiled roofs, if they want their constructions to be approved for occupant use. These codes come from the International Residential Code, or IRC, which is maintained by the International Code Council. Founded in 1994, this nonprofit organization combined the three national codes existing at the time, streamlined any duplication and eliminated conflicting rules. Its goal is to help “the building safety community and construction industry provide safe, sustainable and affordable construction through the development of codes and standards used in the design, build and compliance process.”

Clay and Concrete

• Both clay and concrete tile are available in many colors, and are naturally weather-resistant. Clay tiles are colorfast – which means their tints improve rather than fade over time. Concrete is long-lasting, with a minimum lifespan of 50 years, depending on climate. The IRC recommends a minimum pitch of 2.5:12 for these materials. Ratios from that minimum up to 4:12, which are considered low pitch, require double underlayment. These linings are applied starting at and parallel to the eaves, in 36-inch-wide strips, with a 19-inch overlap for successive sheets. Slopes 4:12 or greater, which are considered high pitch, need only one layer of underlayment.

Slate

• Slate tiles, whether natural or synthetic, are expensive, but they can add value to a home because of their appearance. They last from 60 to 200 years, with their main problems lying in the fastening material, which can rust if made from corrosive substances. Slate tile requires a pitch of 4:12 or greater. Additionally, if the climate can cause backups of water as ice under the eaves, the tile requires at least two layers of underlayment cemented together. In areas with high winds, the underlayment must be attached with corrosion-resistant fasteners according to manufacturer’s instructions.