Roof pitch

Roof pitch Relates to the slope and inclination angle of a roof in building construction. A roof is considered pitched with a gradient greater than 15 degrees or a slope greater than 3.215 in 12. The primary purpose of a pitched roof is to redirect rainwater. In general, the pitch of the roof is proportional to the amount of 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, being roof-dominated 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 26.5 degrees.
Carpenters frame rafters to "pitch" a roof. A 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] 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 foot (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.