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Roof Pitch Determines Your Choice Of Roofing Materials


Roof Pitch

Roof Pitch - From Low to Steep

Copyright Lee Wallender - Licensed to About..com
When choosing roofing materials, it may seem that you have an infinite choice of any material on the market…asphalt, composite, metal, wood shake. The world is your oyster, right? Not so. One of the many factors which limit your choice of roofing materials is pitch.

By pitch, we mean the angle of your roof. Let’s look at two extremes. Many houses built beginning in the 1960s had practically a zero pitch; in other words, except for a negligible slope to drain water, the roof was almost flat. The other extreme are the roofs on Victorian-era houses, which are sharply angled and steeply pitched.

How Roof Pitch Is Measured

For roof pitch, you will see designations such as 2/12 or 7/12. The first number denotes the vertical (height) and the second number denotes the horizontal (length). So, a roof pitch of 5/12, which also happens to be a common roof pitch, means that for every 12 feet, the roof drops 5 feet (or rises 5 feet, however you choose to look at it—same thing).

Extremes range from zero to 12/12. More likely, you will find roof pitches in the range of 4/12 up to 8/12.

Low Roof Pitches: Built-Up and “Torch-Down” Roofing

Roof pitches in the lower ranges, such as 1/12 up to 3/12 are found in more urban, contemporary style houses and, ironically, in industrial buildings and shacks. So, the type of roofing that you find in these buildings tends to be built-up roofing composed of tarpaper roll and hot tar. A “torch-down” roof is one that is softened and melted into place by the workers’ propane torches. The reason you cannot have conventional shingles on the low-pitched roof is that the water does not drain off fast enough, which would allow water to permeate within the shingles. Basically, you need a watertight seal to allow for the slow drainage of water.

Medium Pitches: Asphalt and Composite

Asphalt shingles or composition shingles are the most popular kind of shingle and are the most serviceable type of shingle in terms of roof pitch. Asphalt shingles can start as low as 4/12 pitch, going all the way up to a 12/12 pitch.

Wood Shake Shingles: Steeper Roof Pitch

Wood shake shingles are more susceptible to leakage than composite or asphalt, because the shingles do not lock together as tightly or lay as flat as do composite and asphalt. You will find that wood shake shingles with more exposure to the exterior are even less capable of tolerating the lower pitches. Wood shake shingles are good for pitches from 5/12 on up to 12/12.

Finally, note that these are common types of roofing materials and pitches; we have not covered all types. Also, these designations are not mutually exclusive. For instance, a torch-down roof, while commonly used for extremely low-pitched roofs, can also be used for steeper pitches if so desired.

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