Roof pitch

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 (slope greater than 3.215 in 12).

Carpenters frame (build) 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 (lean-to, single or mono-) pitched roof has twice the pitch as a gable (double or dual-) pitched roof has for the same span. [Walker's Building Estimator's Reference Book] Having two gradient exposure planes, what most people call a "pitched roof" is 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 (without hip or valley) 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 and, or, differing slopes (like two opposed shed roofs with differing pitches) 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 (in) per 1 ft or as a ratio of inches per 12 in; and commonly referred to with units of, less correctly and confusingly, "pitch" (e.g., for a slope of 1/3, "4 pitch(es)" is 4 in of rise over 1 ft of run and "4:12 pitch" is 4 in of rise over 12 in of run). In the UK, Australia and many other places, roof pitches given in degrees (°) are inclinations.

Notes


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