What it is called, by market
One concept, four markets. Where a name means something else locally, the card says so rather than leaving you to find out on site.
United Statesyours
Same word, different thingpitch (rise in 12)
also 6:12, 6 in 12, slope
A bare number means inches of rise per 12 inches of run, NOT degrees — so "a 6 pitch" is about 26.6 degrees, not six.
Canada
Same word, different thingpitch (rise in 12)
also 6:12, slope
As the United States: the run is 12 even where the rest of the drawing is metric, because the convention travelled with the framing practice.
United Kingdom
Same word, different thingpitch (degrees)
also fall, rise and run
British practice quotes the ANGLE in degrees, so a pitch given as a bare number means degrees — the opposite reading from the American one.
Australia
Same word, different thingpitch (degrees)
also fall, roof slope
As the UK, degrees — and manufacturers' minimum pitches for tiles and sheeting are published in degrees, so converting from a ratio is a required step rather than a convenience.
The governing standard, by market
United Kingdom
BS 5534
Slating and tiling — including minimum pitch and fixing requirements.
United States
IRC Chapter 9
Roof assemblies, including minimum slopes by covering type.
Calculators for this
Each works in either measurement system, and the terminology on the page follows whichever market you have selected.
Frequently asked questions
- Is a 6 pitch six degrees?
- No, and this is the one that produces a roof of the wrong shape. In American and Canadian usage a pitch of 6 means six units of rise for every twelve of run — an angle of about 26.6 degrees. In British and Australian usage a pitch of 6 means six DEGREES, which is a nearly flat roof. The two readings of the same bare number are far apart, and neither convention marks itself: a drawing saying "pitch 6" is unambiguous only to a reader who knows which market drew it. Converting is straightforward arithmetic — the angle is the arctangent of rise over run — but it has to be done deliberately, and the convention has to be stated on anything read across markets.
- What is the difference between pitch and slope?
- In careful American usage they are different ratios, though the words are used loosely. Slope is the rise over the horizontal RUN — the 6-in-12 figure — and it is what framing, rafter lengths and covering minimums are worked from. Pitch, in its older and stricter sense, is the rise over the total SPAN of the building, so the same roof has a slope of 6 in 12 and a pitch of one quarter. In everyday use the word pitch has taken over the slope meaning almost everywhere, which is why the strict sense mostly appears in older texts and in some truss literature. If a document uses both words for different numbers, that is probably why.
- Why do minimum pitches matter so much?
- Because a roof covering sheds water rather than sealing against it, and below a certain angle it stops shedding fast enough. Tiles, slates and profiled sheets each have a manufacturer's minimum pitch, below which wind-driven rain is pushed back up under the laps faster than it drains away — so the covering leaks even though every piece is correctly fixed. The minimum is not a single number per material: it depends on the lap, on the underlay, on the exposure of the site, and often on whether the sheets are sealed at the laps. Below the lowest tiled pitch the construction changes entirely to a continuously supported membrane, which is a different trade and a different detail.