How Much Roof Pitch Should Be Used?

Definition

• Pitch, also known as slope or grade, is the way a roof surface angles from the horizontal toward the top. It is usually expressed as a ratio of the number of units of rise over 12 units of horizontal movement. So a roof that goes up three inches for every 12 inches it goes forward has a pitch of 3:12. Low-pitch roofs, with a slope of 5:12 or under, are the easiest and cheapest to install because they are walkable. Medium-pitch roofs from 6:12 to 9:12 are not walkable. They require roofing jacks and planks for installation and are more expensive. High pitch roofs ranging from 10:12 to 12:12 -- 45 degrees -- are dangerous and difficult, requiring special protectons and fall arrest equipment. It is the most expensive to construct.

Asphalt

• Homeowners can use as steep a pitch as they desire, limited only by design and budget. However, minimum pitches depend on the materials used. Local building codes regulate these measurements, which are based on the International Residential Code. Asphalt shingle, for example, is the most popular roofing material in the U.S. because of its low cost and durability. It needs a minimum 2:12 slope and requires double underlayment for slopes up to 4:12. Underlayment is a protective sheet that sits between the shingle and the roof deck.

Tile

• Clay and concrete tile are long-lasting, and grants discounts with home insurance because they are naturally fire resistant. They require a minimum slope of 2.5:12. Like with asphalt, these materials require double underlayment for slopes up to 4:12. Slate tile is expensive and heavy but can add to the value of a home because of its dimensionality. It must have a minimum 4:12 slope. Materials similar to slate must also use the same slope.

Wood

• Wood is the oldest roof covering, and is popular because of its natural texture that can be stained a variety of colors. It does require constant upkeep and repair to maintain durability. Wood shingles, which are tapered and smooth on two faces, need a minimum deck of 3:12. Wood shakes, which are thicker and smooth on just one face, must also use the same slope.