Question answered
What is the minimum pitch for roof tiles?
The short answer
The minimum pitch for roof tiles depends on the tile. Marley lists 35° for its concrete plain tile, 30° to 40° for its clay plain tiles and between 12.5° and 25° for its interlocking concrete tiles. Natural slate is 20° at moderate exposure under BS 5534. These are product minimums, so the maker's sheet for the exact tile should be read before any roof is laid or recovered.
Every tile and slate has a lowest pitch below which it should not be laid. The figure changes with the product, so the maker's data sheet settles the matter for any particular roof.
Why a tile needs a minimum slope
Pitch is the angle of the roof slope measured up from the horizontal. A tiled covering sheds water because gravity carries it down across the laps, and on a flatter slope the water moves more slowly and a gust can shove it backwards under the tile above. Below a certain angle a perfectly good tile begins to let water past its joints, though nothing about the tile has changed.
That angle comes from testing and is printed by each maker. There is no single national figure covering all tiles. Marley also states that on a pitch below 30° the windward slope can feel severe suction, so a low roof has to drain well and be held down well. Drainage and wind are the two reasons shallow slopes are where tile trouble tends to start, and why a tile that suits one house can fail on the next.
Plain tiles and pantiles: the Marley figures
Plain tiles are small and double-lapped, so they need a steeper slope than the large interlocking kinds, because each course has less overlap to resist water pushed up the roof. Marley's minimum-pitch page gives the examples below, and every product also has its own data sheet. Treat the table as a guide to the pattern, not as a substitute for the sheet that comes with the tiles you are actually buying.
| Marley product | Minimum pitch |
|---|---|
| Concrete plain tile | 35° |
| Clay plain, Canterbury | 40° |
| Clay plain, Ashdowne | 35° |
| Clay plain, Hawkins | 30° |
| Lincoln clay pantile | 15° |
A plain-tiled roof that seems quite shallow from the road may still sit well above these numbers, and one that looks steep may not. What matters is the measured angle of the slope, never the impression it gives from the pavement or the garden gate.
Interlocking concrete tiles and natural slate
Large interlocking tiles lock sideways and have deep side channels, so they cope with lower slopes. Marley's figures run from 12.5° for Mendip 12.5 and 15° for Wessex, through 17.5° for Edgemere, up to 22.5° for Double Roman and Ludlow Plus and 25° for Anglia. The spread shows how much depends on the profile, and a change of profile can change the price of a re-cover, as our tiled roof repair cost guide explains.
Natural slate follows another rule. Cupa Pizarras, quoting BS 5534:2014+A2:2018, puts natural slate at 20° minimum for moderate exposure, using a 500 mm slate with a 115 mm headlap. The headlap, which is the overlap between courses, has to grow as the slope falls. It also advises against hook fixings on a slope of less than 25°. Slate is a separate subject, but the principle matches that for tiles: the lower the slope, the less room for error.
When a roof sits below the limit
Low pitches turn up on porches, lean-to extensions, dormer cheeks and old outbuildings where the wall height fixed the angle. They also turn up when someone recovers a roof with a different tile from the original. A slope that suited a pantile may be too shallow for a plain tile, and the new covering can leak where the old one never did. Matching a tile by look alone, without checking its limit, is a common way into that problem, and how to match old roof tiles covers the other half of the choice.
Marley asks that where the rafter length is more than 6 metres, or the site is rated severe for driving rain, the tile's suitability is confirmed with the maker. The right response is to check the real tile, the measured angle and the exposure with the supplier, and to keep the reply on file with the job.
Working out the pitch of your own roof
A rough measure is possible from the loft. Hold a spirit level flat against a rafter, measure how far the rafter drops over a set distance and compare the result with the maker's chart. A surveyor measures the angle precisely and checks it against the product, which is more reliable than guessing.
A low pitch also changes the detail beneath the tiles. On a shallow roof the underlay, the eaves and the gutter line matter more, because water has less slope to help it away, and our note on eaves felt support deals with the eaves side. If a slope is below the limit for its covering, the sound choices are a different covering that suits the angle or a steeper structure. Hoping for the best is not one of them. The range of tiled work we carry out is on the pitched roofing hub.
Pitch and the data sheet
Can a tile go below its minimum pitch if the underlay is strong?
Only if the maker's own literature allows it for that product. A better underlay is a second line of defence, not a way round a tested limit. Ask the tile maker's technical service and keep the reply with your papers before any covering goes on.
Do I need to know my roof's pitch before asking for a quote?
No. The survey measures it. A rough idea helps, as does the tile type if you know it, but photographs of the slope and a note of any leaks are enough for us to start. The written quote follows once the angle and the covering have been checked.
Tell us about your roof
Describe what is happening and we will call you back to arrange a visit.
- Photographs of what we find
- A written quote with one total price
- Or call 01903 299063
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