Roof pitch is the steepness of a

roof A roof ( : roofs or rooves) is the top covering of a building, including all materials and constructions necessary to support it on the walls of the building or on uprights, providing protection against rain, snow, sunlight, extremes of temper ...

expressed as a ratio of inch(es) rise per horizontal foot (or their metric equivalent), or as the angle in degrees its surface deviates from the horizontal. A flat roof has a pitch of zero in either instance; all other roofs are pitched. A roof that rises 3 inches per foot, for example, would be described as having a pitch of 3 (or “3 in 12”).

Description

The pitch of a roof is its vertical 'rise' over its horizontal 'run’ (i.e. its

span Span may refer to: Science, technology and engineering * Span (unit), the width of a human hand * Span (engineering), a section between two intermediate supports * Wingspan, the distance between the wingtips of a bird or aircraft * Sorbitan ester ...

), also known as its '

slope In mathematics, the slope or gradient of a line is a number that describes both the ''direction'' and the ''steepness'' of the line. Slope is often denoted by the letter ''m''; there is no clear answer to the question why the letter ''m'' is use ...

'. In the imperial measurement systems, "pitch" is usually expressed with the rise first and run second (in the US, run is held to number 12; e.g., 3:12, 4:12, 5:12). In metric systems either the angle in degrees or rise per unit of run, expressed as a '1 in _' slope (where a '1 in 1' equals 45°) is used. Where convenient, the

least common multiple In arithmetic and number theory, the least common multiple, lowest common multiple, or smallest common multiple of two integers ''a'' and ''b'', usually denoted by lcm(''a'', ''b''), is the smallest positive integer that is divisible by bot ...

is used (e.g., a '3 in 4' slope, for a '9 in 12' or '1 in 1 1/3').

Selection

Considerations involved in selecting a roof pitch include availability and cost of materials, aesthetics, ease or difficulty of construction, climatic factors such as wind and potential snow load, and local building codes. The primary purpose of pitching a roof is to redirect wind and precipitation, whether in the form of rain or snow. Thus, pitch is typically greater in areas of high rain or snowfall, lower in areas of high wind. The steep roof of the tropical

Papua New Guinea Papua New Guinea (abbreviated PNG; , ; tpi, Papua Niugini; ho, Papua Niu Gini), officially the Independent State of Papua New Guinea ( tpi, Independen Stet bilong Papua Niugini; ho, Independen Stet bilong Papua Niu Gini), is a country i ...

longhouse A longhouse or long house is a type of long, proportionately narrow, single-room building for communal dwelling. It has been built in various parts of the world including Asia, Europe, and North America. Many were built from timber and often rep ...

, for example, sweeps almost to the ground. The high, steeply-pitched

gable A gable is the generally triangular portion of a wall between the edges of intersecting roof pitches. The shape of the gable and how it is detailed depends on the structural system used, which reflects climate, material availability, and aesth ...

d roofs of Northern Europe are typical in regions of heavy snowfall. In some areas

building code A building code (also building control or building regulations) is a set of rules that specify the standards for constructed objects such as buildings and non-building structures. Buildings must conform to the code to obtain planning permission ...

s require a minimum slope.

Buffalo, New York Buffalo is the second-largest city in the U.S. state of New York (behind only New York City) and the seat of Erie County. It is at the eastern end of Lake Erie, at the head of the Niagara River, and is across the Canadian border from South ...

and

Montreal Montreal ( ; officially Montréal, ) is the List of the largest municipalities in Canada by population, second-most populous city in Canada and List of towns in Quebec, most populous city in the Provinces and territories of Canada, Canadian ...

, Quebec, Canada, specify 6 in 12, a pitch of approximately 26.6 degrees. A ''flat'' roof includes pitches as low as 1/2:12 to 2:12 (1 in 24 to 1 in 6), which are barely capable of properly shedding water. Such ''low-slope'' roofs (up to 4:12 (1 in 3)) require special materials and techniques to avoid leaks."Slope" def. 1. Schmid, Karl F.. ''Concise encyclopedia of construction terms and phrases''. New York: Momentum, 2014. Print. ''Conventional'' describes pitches from 4:12 (1 in 3) to 9:12 (3 in 4). ''Steep'' is above 9:12 (3 in 4) (21:12) (7 in 4) and may require extra fasteners. US convention is to use whole numbers when even (e.g. "three in twelve") or the nearest single or two-digit fraction when not (e.g. either "five and a half in twelve" or "five point five in twelve", each expressed numerically as 5-1/2:12 and 5.5:12) respectively. Definitions vary on when a roof is considered pitched. In degrees, 10°(2 in 12 or 1 in 6) is considered by at least one reference a minimum. In trigonomic expression, exact roof slope in degrees is given by the arctangent. For example: arctan(3/12)=14.0° Framing

carpenter Carpentry is a skilled trade and a craft in which the primary work performed is the cutting, shaping and installation of building materials during the construction of buildings, Shipbuilding, ships, timber bridges, concrete formwork, etc. ...

s cut

rafter A rafter is one of a series of sloped structural members such as wooden beams that extend from the ridge or hip to the wall plate, downslope perimeter or eave, and that are designed to support the roof shingles, roof deck and its associated ...

s on an angle to "pitch" a roof. Lower pitched roof styles allow for lower structures with a corresponding reduction in framing and sheathing materials.

Historic expressions of roof pitch

Historically, roof pitch was designated in two other ways: A ratio of the ridge height to the width of the building (span)"Pitch" def. 24.c. ''Oxford English Dictionary'' Second Edition on CD-ROM (v. 4.0) © Oxford University Press 2009 and as a ratio of the rafter length to the width of the building."Pitch" def. 2. Knight, Edward Henry. ''Knight's American mechanical dictionary: being a description of tools, instruments, machines, processes, and engineering; history of inventions; general technological vocabulary; and digest of mechanical appliances in science and the arts''.. vol. 2. New York: J.B. Ford and Co., 1874. 1719. Print. Commonly used roof pitches were given names such as: * Greek: the ridge height is 1/9 to 1/7th the span (an angle of 12.5° to 16°); * Roman: the ridge height is 2/9ths to 1/3 the span (an angle of 24° to 34°); * Common: the rafter length is 3/4 the span (about 48°); * Gothic: the rafters equal the span (60°); and * Elizabethan: the rafters are longer than the span (more than 60°).

References

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External links

Aerial Roof Measurements
Building Building engineering

Description

Selection

Historic expressions of roof pitch

See also

References

External links