Minimum pitch
What is the minimum roof pitch for tiles?
No single angle suits every tile: each product has its own published limit. Below: Marley clay and concrete figures, slate, and what a shallow roof needs.
The short answer
There is no single minimum pitch for tiles, because each tile has its own published limit. Marley's published list starts at 15° for its Lincoln pantile and tops out at 40° for a clay tile it calls Canterbury, while its concrete tiles run from 12.5° to 35°. For natural slate, Cupa says BS 5534 gives 20° at moderate exposure with a 500 mm slate and a 115 mm overlap. Check the maker's sheet for the exact tile before anything is ordered.
4 min read · Part of Pitched roofing
Why every tile has its own limit
Pitch is the angle of the roof slope above horizontal, measured in degrees. A steep slope sheds water quickly, so rain has little time to be driven up under the tile edges. A shallow one sheds it slowly, so each tile has to be designed to cope with it. A flat-faced plain tile and a deep profile pantile deal with water differently, which is why their limits differ so widely.
Two things sit behind any figure below. The first is that these are the makers' published minimums, and your own roof also has to satisfy the data sheet of the tile and BS 5534. The second is that exposure counts. Cupa says that tall buildings, and those on hills, slopes or the coast, receive a higher exposure grade, so a limit quoted for moderate exposure may not be enough on an open site. On survey the pitch is measured with a digital level, and the data sheet for the tile in question is read against it. A figure taken from the ground or from a drawing is not enough, since the roof may have settled or been altered since it was built.
Clay tile limits from Marley
Marley's published minimum pitches for its clay tiles run across a wide spread, with the range tile at the top and the pantile at the bottom.
| Tile | Minimum pitch |
|---|---|
| Canterbury | 40° |
| Ashdowne | 35° |
| Hawkins | 30° |
| Acme Single Camber | 30° |
| Lincoln pantile | 15° |
Canterbury here is the name of a Marley tile and has nothing to do with the city, so it says nothing about roofs in Canterbury or anywhere else. The tile that suits a roof depends on its slope, and a roof pitched at 25° cannot take any of the first four, however well they would suit the look of the street. The same applies in reverse: a pantile on a steep slope may be allowed, but the look and the fixing still have to be right for it.
A roof may also have more than one angle. A porch, an extension or a garage roof on the same house can sit far shallower than the main slopes, so each slope is measured and checked against its own tile. We take the pitch from the rafters in the loft where we can, and from the outside where we cannot.
Concrete tiles and natural slate
Marley's concrete tiles have lower limits on the whole, and several sit well below 20°.
| Tile | Minimum | Tile | Minimum |
|---|---|---|---|
| Plain | 35° | Edgemere | 17.5° |
| Modern-Duo | 17.5° | Double Roman | 22.5° |
| Mendip | 15° | Mendip 12.5 | 12.5° |
| Ludlow Major | 22.5° | Ludlow Plus | 22.5° |
| Wessex | 15° | Anglia | 25° |
Marley also lists the Ashmore at 22.5°. Natural slate follows Cupa's reading of BS 5534: a minimum of 20° at moderate exposure with a 500 mm slate and a 115 mm overlap, and hooks never used below 25°. Those slate figures move with the exposure and the overlap. If you are weighing slate against tile, the pitch narrows the field first, and cost and looks come second. A roof pitched near the bottom of a tile's range leaves little margin, so the survey names a safer choice rather than selling the tile that merely fits on paper.
The Planning Portal and the Building Regulations do not set a pitch for tiles; the limits above come from the makers and from BS 5534.
When the roof is shallower than the tile allows
A tile laid below its limit is a tile used outside what its maker published, which is a risk we do not take on a customer's roof. If the slope is too shallow for the tile you want, there are only a few sound routes:
- choose a tile whose minimum pitch is lower than your roof's angle, such as a pantile or a low-pitch concrete profile
- change the covering to one designed for the pitch, which can mean a different material altogether
- re-form the roof structure to a steeper pitch, which is a larger job with its own approvals
Changing the covering has knock-on effects. A new covering that is 15 per cent or more heavier needs Building Regulations approval, and a re-roof touching less than 25 per cent of the building envelope and less than 50 per cent of the roof normally stays clear of an application under the Planning Portal test. Our clay against concrete page covers the comparison, and the pitched roofing page shows how the work runs.
More questions
Does the minimum pitch rise on an exposed site?
It can. Cupa reports BS 5534's 20° for natural slate only at moderate exposure, with a 500 mm slate and a 115 mm overlap, and says exposed sites are graded higher. A tile's published minimum is a starting point, and the data sheet and BS 5534 then set what the actual site needs.
Is the Canterbury tile pitch the rule for roofs in Canterbury?
No. Canterbury is the name of a Marley clay tile, which has a published minimum pitch of 40°. It has no connection with the city or with roofs there. Roofs in any town take the tile whose published limit suits the slope, and the survey measures the pitch to confirm what that is.
Tell us what's wrong with the roof.
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