Roof pitch
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In building construction, roof pitch is a numerical measure of the steepness of a roof, and a pitched roof is a roof that is steep.
The roof's pitch is the measured vertical rise divided by the measured horizontal span, the same thing as what is called "slope" in geometry. Roof pitch is typically expressed as a rational fraction. Having twice as much rise per span, a shed pitched roof has twice the pitch as a gable pitched roof has for the same span.[1]
A roof is considered pitched if its pitch is greater than 3.215 in 12, or equivalently if its angle from horizontal is greater than 15 degrees. The primary purpose of a pitched roof is to redirect rain or snow. Typically, the pitch of roofs is greater in areas where there is more precipitation. Houses in areas of low rainfall frequently have roofs of low pitch while those in areas of high rainfall and snow have steep roofs. The longhouses of Papua New Guinea, for example, is a roof-dominated form of architecture, the high roofs sweeping almost to the ground. The high steeply-pitched roofs of Germany and Holland are typical in regions of snowfall. In parts of North America, including the cities of Buffalo, New York and Montreal, Quebec, Canada, building codes require a minimum slope of 6 inches in 12 inches, a pitch of approximately 26.6 degrees.
Carpenters frame rafters to "pitch" a roof. Having two gradient exposure planes, often called a "pitched roof" is more correctly a "double-pitched roof". Mono-pitched roofs have one gradient exposure plane. Gable and other split opposed-slope pitched roofs allow for shorter primary structures with a corresponding conservation of materials.
Example: The pitch of a shed roof with an 8 ft rise (above wall height) by a 24 ft span (between exterior supporting walls) will be 1/3. The pitch of a gable roof with a 4 ft rise by a 24 ft total span will be 1/6. However, the slopes of each roof will be the same (1/3).
A simple shed roof is pitched with one plane. A simple gable roof is pitched with two equal opposed-slope planes. A simple salt box roof is pitched with opposed planes of unequal split or differing slopes sharing a common ridge. A combined pitched form has a vertical offset along a common ridge line. Hip and mansard (quad-pitched, very often mistakenly called double-pitched, hip) roofs are pitched with uniform slopes on all sides. Other roof styles include flat (unpitched), domed, gambrel (quad-pitched, very often mistakenly called double-pitched, gable or barn), and A-frame, barrel-vaulted. The lower plane's slope is steeper than the upper plane's slope on quadruple-pitched roofs.
In the United States, slope is typically given in inches per 1 foot or as a ratio of inches per 12 inches; and commonly referred to with units of "pitch" (e.g., for a slope of 1/3, "4 pitch(es)" is 4 inches of rise over 1 foot of run; "4:12 pitch" is 4 inches of rise over 12 inches of run). In the UK, Australia and many other places, roof pitches given in degrees (°) are inclinations.
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[edit] Roof Pitch Calculation Formula
Calculating roof pitch as rational is achieved by the following formula:
Roof pitch = (rise / run) X 12
Where the roof run is measured from the point where the level touches the roof. It equals the half of the root width.
[edit] Notes
- ^ Walker's Building Estimator's Reference Book
[edit] See also
[edit] External Links
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