View source for Roof pitch

{{short description|Measure of roof steepness}}
[[File:Roof Pitch (American 12-based).png|thumb|Display of roof pitches 1:12 through 18:12]]
[[File:Anne Hathaway's cottage - geograph.org.uk - 752203.jpg|thumb|right|A roof made of [[thatch]], one of the oldest roofing materials, needs a steep pitch to drain properly]]
[[File:Kamena kuca u Pokreveniku.jpg|thumb|right|Some types of stone roof have a very restrictive roof pitch, which can lead to leaking]]
[[File:Slater at work, Rothesay, Isle of Bute.jpg|thumb|Working on roofs with pitches too steep for safety requires a staging of scaffolding boards secured with ''roof brackets'']]
[[File:Pitch gauge measuring slope on a roof.jpg|thumb|A pitch gauge measuring the slope of an asphalt shingle roof]]
'''Roof pitch''' is the steepness of a [[roof]] 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 [[Roof#Design elements|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 (architecture)|span]]), also known as its '[[slope]]'.
In the [[Imperial and US customary measurement systems|imperial measurement systems]], "pitch" is usually expressed with the rise first and run second (in the US, run is held to number 12;<ref>{{Cite web|url=https://roofonline.com/roof-slope-multiplier|title=Roof Slope Multiplier|website=Roof Online|language=en-US|access-date=2018-05-19}}</ref> 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, a [[Irreducible fraction|reduced ratio]] is used (e.g., a '3 in 4' slope, for a '9 in 12' or '1 in {{frac|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,<ref>"Pitch" Sturgis, Russell. ''A dictionary of architecture and building: biographical, historical, and descriptive''. New York: The Macmillan Co. ;, 1901. 152. Print.</ref> 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]] [[longhouse]], for example, sweeps almost to the ground. The high, steeply-pitched [[gable]]d roofs of Northern Europe are typical in regions of heavy snowfall. In some areas [[building code]]s require a minimum slope.  [[Buffalo, New York]] and [[Montreal]], Quebec, Canada, specify 6 in 12, a pitch of approximately 26.6 degrees.<ref>[https://www.thisiscarpentry.com/2011/07/29/miter-angles-miter-saws/] Miter angles and miter saws, thisiscarpentry.com</ref>
A [[flat roof|''flat'']] roof includes pitches as low as {{frac|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.<ref name="Schmid" >"Slope" def. 1. Schmid, Karl F.. ''Concise encyclopedia of construction terms and phrases''. New York: Momentum, 2014. Print.</ref> ''Conventional'' describes pitches from 4:12 (1 in 3) to 9:12 (3 in 4).<ref name="Schmid" /> ''Steep'' is above 9:12 (3 in 4)<ref name="Schmid" /> (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 {{frac|5|1|2}}:12 and 5.5:12) respectively.
Definitions vary on when a roof is considered pitched.  In [[degree (angle)|degrees]], 10° (2 in 12 or 1 in 6) is considered by at least one reference a minimum. <ref>Dictionary of Architecture & Construction, C.M.Harris.</ref>
In trigonometric expression, exact roof slope in degrees is given by the arctangent. For example: arctan({{frac|3|12}}) = 14.0°.
[[Framing (construction)|Framing]] [[carpenter]]s cut [[rafter]]s on an angle to "pitch" a roof.  Lower [[List of roof shapes|pitched roof styles]] allow for lower structures with a corresponding reduction in framing and sheathing materials.
==Historic expressions of roof pitch==
[[File:Rathaus von Sölden im Schwarzwald.jpg|thumbnail|A building in the [[Black Forest]] of Germany with a pitched roof]]
Historically, roof pitch was designated in two other ways: A ratio of the ridge height to the width of the building (span)<ref>"Pitch" def. 24.c. ''Oxford English Dictionary'' Second Edition on CD-ROM (v. 4.0) © Oxford University Press 2009</ref> and as a ratio of the rafter length to the width of the building.<ref name="Knight" >"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.</ref>
Commonly used roof pitches were given names such as:
* Greek: the ridge height is {{frac|1|9}} to {{frac|1|7}} the span (an angle of 12.5° to 16°);
* Roman: the ridge height is {{frac|2|9}} to {{frac|1|3}} the span (an angle of 24° to 34°);
* Common: the rafter length is {{frac|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°).<ref name="Knight" />
== See also ==
*[[List of roof shapes]]
*[[Shed roof]]
*[[Flat roof]]
*[https://civilchapola.com/pitched-roof/ Types of Pitched roof]
== References==
{{reflist}}
==External links==
*[http://www.tomcomknowshow.com/how-to-calculate-a-roof-pitch-in-degrees.html How to determine roof pitch]
*[http://shedbuilder.info/roof-pitch-calculator.html Roof pitch calculator]
*[https://stroyka.expert/en/calcs/roof/roof-pitch-calculator.html Online roof pitch calculator]
[[Category:Building]]
[[Category:Building engineering]]
[[Category:Roof construction]]