The short answer
The minimum pitch depends on the tile. Marley lists clay plain tiles from 30 to 40 degrees, its Lincoln clay pantile at 15 degrees and its concrete tiles from 12.5 to 35 degrees. Sandtoft's Old English Pantile needs 30 degrees. Check the maker's data sheet for the product you are choosing before you commit, since the figure also moves with exposure, headlap and fixings.
What pitch means and how it is measured
A roof's pitch is its slope angle above the horizontal, given in degrees. A 30 degree roof rises roughly as much for every metre as a steep garden path would, while a 15 degree roof looks nearly flat from the street. It is measured on the slope itself, not on the ridge line, and a roofer can read it with an inclinometer or from a drawing. Rafter pitch and finished pitch are the same on an ordinary roof.
The reason the number matters is simple. Every tile sheds water by overlapping the one below, and the rain must run off faster than it can creep sideways or back up beneath the laps. In a heavy shower the water also meets wind, which pushes it up the slope, so the roof is working against more than gravity. On a steep slope gravity does most of the work. On a shallow one, wind-driven rain and capillary action can push water under the tile, so manufacturers set a floor below which they will not stand behind the product.
Published minimum pitches for common tiles
Marley's published guidance lists minimum pitches for its clay and concrete ranges. Sandtoft's product data sheet, from Wienerberger, gives the Old English clay pantile. These are manufacturer figures, read on 13 October 2026, and every product is different.
| Tile | Minimum pitch |
|---|---|
| Marley clay plain: Canterbury | 40 degrees |
| Marley clay plain: Ashdowne | 35 degrees |
| Marley clay plain: Hawkins | 30 degrees |
| Marley Lincoln clay pantile | 15 degrees |
| Marley concrete plain | 35 degrees |
| Marley concrete Edgemere | 17.5 degrees |
| Marley concrete Mendip (smooth) | 15 degrees |
| Sandtoft Old English Pantile | 30 degrees |
Natural slate under BS 5534 is quoted at 20 degrees in moderate exposure, with the right headlap. Cupa Pizarras adds a fixing rule for slate: no hook fixings on a pitch below 25 degrees. Cotswold stone slates are traditionally laid at 47 to 55 degrees on old roofs, which is a custom rather than a limit set by a maker.
Why one clay tile needs twice the pitch of another
A plain tile is small, flat and double-lapped, which means two thicknesses of tile sit over each part of the slope. It is relatively simple to make watertight on a steep roof, but a gentle one lets water creep through the joints. An interlocking or pantile profile carries water in channels and locks to its neighbours, so it can work on shallower roofs. That is why the Lincoln pantile sits at 15 degrees and the Canterbury plain tile at 40, though both are clay.
Headlap, the overlap between a tile and the one two courses above, also depends on the pitch. Sandtoft gives the Old English Pantile a headlap of 75 mm and a fixed gauge of 290 mm. A shallower roof needs a bigger overlap, and a steeper one can manage with less. If you want to compare the two formats directly, see plain tiles or interlocking tiles.
Why you check the product data sheet
The table above is a guide, not a specification. A product data sheet also sets out the headlap, the gauge and the fixing rules for the tile you have chosen. Exposure matters as well, and Cupa Pizarras defines severe exposure for slate as any area within 30 miles of a west-facing coastline. That is a published definition used in headlap tables, not a statement about any one valley, and we make no claim about local weather.
The pitch on your roof may not be what you think. Roofs altered over the years often vary from slope to slope, and a dormer cheek or a lean-to can be lower than the main roof. We measure on survey and photograph the slope. If an existing roof turns out to be below the minimum for the tile on it, our answer on tiles on a low-pitched roof explains why it leaks and what the options are.
What happens if the pitch is below the minimum
A shallow slope is also where underlay and flashings are tested hardest, because water lingers on them for longer. Even above the minimum, a low-pitch roof leaves less margin for a slipped tile or a blocked valley, so repairs there deserve extra care.
Below a tile's minimum, the manufacturer's weather performance no longer applies, and any guarantee on the tile may be affected. A roof may stay dry for years, then leak after one wet and windy spell. Fixes include a covering designed for lower pitches, a different tile profile, a sheet or membrane roof, or a change to the structure to raise the pitch.
Changing the covering has knock-on effects. A heavier tile may mean a structural check, and the Planning Portal says approval is needed where the new covering increases the weight by 15 per cent or more. Re-covering less than 50 per cent of the roof, while touching less than 25 per cent of the building envelope, does not normally call for an application. Where one is needed we talk through why and send it to building control for you. The quote you get after the survey covers the whole job, and we write the measured pitch of each slope, in degrees, on it. For roof tiles that have slid on a shallow slope, see slipped roof tiles, and for the whole service, pitched roofing.