The pitch of a roof is important when making certain roof drainage calculations (see Roof Drainage). ![]() The pitch of a roof is an important factor in figuring out how much roofing material will be needed when installing a new roof, because it allows you to accurately calculate the surface area of the roof (see How to Find the Area of a Roof).The pitch of a roof determines what roofing materials can be used on the roof (see Minimum Roof Pitch for Every Roofing Material).Low-slope roofs use a different set of materials, have different installation techniques, and have far different maintenance requirements than steep-slope roofs. Low-slope roofs may drain slowly and they depend on a continuous waterproof barrier to keep water out of the building, while pitched roofs depend on gravity and slope to get water off the roof as fast as possible while ensuring the water doesn’t flow up and underneath the shingles or tiles. Generally, although there are exceptions (such as the case with asphalt shingles mentioned above), low-slope roofs will have a different fundamental method of waterproofing than pitched roofs. Any use of asphalt shingles, for example, on a roof with a pitch below 3-in-12 is considered a “low-slope application” of the shingles. In all the technical literature, the cut-off point is 3-in-12. Low-slope roofs typically have membrane-style roof coverings and steep-slope roofs typically have shingles or tiles.īecause shingles and tiles can also sometimes be installed on roofs that have a pitch under 3-in-12 (as low as 2-in-12 if special underlayment requirements are met) there is often confusion about where the cut-off point is between low-slope and pitched roofs. More casually, roofers who specialize in pitched roofing will often use “steep slope” to refer to roofs with a 9/12 or greater pitch. (from OSHA’s Safety and Health Regulations for Construction, Section 1926.500(b)(2)). In the context of OSHA’s safety guidance, “ steep roof means a roof having a slope greater than 4-in-12 (vertical to horizontal)”. “Pitched” or “steep-slope” roofing refers to any roof with a slope of 3-in-12 or above (as defined and used in the technical literature of the roofing industry). The technical definition of a low-slope roof is any roof having a slope of less than 3-in-12 (approximately 14 degrees above horizontal). Perfectly flat roofs would be at a much higher risk of overloading and collapsing due to standing water.Ī low-slope roof will typically have a pitch between ¼-in-12 and 2½-in-12. This requirement is intended to ensure that water will drain off the roof. Steep-Slope RoofsĪ low-slope roof is commonly called a “flat roof”, although building codes forbid perfectly flat roofs and require all flat roofs to have some slope. The steepness of a roof may be expressed in degrees or as a percentage (see Ways to Express Roof Slope: Pitch, Degrees, and Percentage). Instead, they express roof slope in degrees. Places that don’t use inches typically don’t use standard roof pitch, either. ![]() ![]() Traditionally, this expression of pitch takes the form “X:12″ or “X-in-12″, where X is the number of units (inches) of vertical rise of the roof and 12 inches is the run.ġ2 is always used for the run because there are 12 inches in a foot, and you are stating how many inches the roof rises over a one foot horizontal span. When using pitch (rather than degrees or percentage), the slope of the roof is given as a ratio of the vertical rise to the horizontal run (rise/run). Roof pitch is a mathematical expression of how steep your roof is.
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