The short answer
There is no single minimum pitch for roof tiles, because it depends on the product. Marley's data gives clay tiles from 15 degrees for the Lincoln pantile to 40 for the Canterbury, and concrete tiles from 12.5 degrees for the Mendip 12.5 to 35 for its plain tile. Read the maker's published sheet for your specific tile, and measure the roof before you choose.
Clay tiles
Marley's guidance on minimum pitch for a roof tile or slate lists these clay products and the lowest angle each should be laid at.
| Tile | Minimum pitch |
|---|---|
| Canterbury | 40 degrees |
| Ashdowne | 35 degrees |
| Hawkins | 30 degrees |
| Acme Single Camber | 30 degrees |
| Lincoln pantile | 15 degrees |
The spread is wide. A traditional plain clay tile such as the Canterbury needs a steep roof, because it relies on a deep overlap and gravity to shed water. The pantile, a larger wave-shaped tile, needs far less.
Those are the figures for one maker. Other clay tile makers publish their own, and an individual tile of the same family can differ by finish or by batch. The maker's sheet for the tile you are buying is the reference.
Degrees are measured from the horizontal, not as a ratio. A 30 degree roof is a moderate slope, steeper than a typical shed roof and shallower than a steep Victorian gable. You can read the pitch from a set of drawings, from a pitch finder, or from the angle of the rafters in the loft.
Our page on repairing a clay tile roof looks at how the type affects repairs.
Concrete tiles
Marley's concrete tiles are listed below, with the smooth versions marked where the figure applies to the smooth finish.
| Tile | Minimum pitch |
|---|---|
| Plain | 35 degrees |
| Edgemere | 17.5 degrees |
| Modern-Duo | 17.5 degrees (smooth) |
| Double Roman | 22.5 degrees (smooth) |
| Mendip | 15 degrees (smooth) |
| Mendip 12.5 | 12.5 degrees |
| Ludlow Major | 22.5 degrees (smooth) |
| Ludlow Plus | 22.5 degrees |
| Wessex | 15 degrees |
| Anglia | 25 degrees (smooth) |
| Ashmore | 22.5 degrees |
The plain tile at 35 degrees needs a steeper roof than any interlocking profile in the list, which goes some way to explaining why interlocking tiles are used on shallow slopes. The lowest figure, 12.5 degrees for the Mendip 12.5, is the opposite extreme from the plain tile, so a swap between two tiles on one roof can be impossible without changing the structure. Our page on interlocking versus plain tiles sets out the difference.
The note about smooth finishes matters. Some figures in the list apply only to the smooth version of a tile, so you cannot assume that the same tile with a different finish is allowed on the same slope. The order of the finish matters when matching an existing roof, because the name on the tile may not state it.
Slate has its own rules
Natural slate is a different case. The slate maker Cupa reads BS 5534 as putting natural slate's floor at 20 degrees, and adds that slate hooks are not for slopes under 25 degrees. A slate roof between those two angles therefore needs another fixing method, such as nails.
The rules here concern the covering. If a roof is below the minimum for a tile, the tile will not do, however good it is. Options are then a different covering made for low slopes, such as a flat roof system or a lead or metal sheet, or changing the pitch of the roof structure, which is major building work.
Slate has a separate page on this site, so we leave the detail there. The point to carry over is that the same logic applies to every covering: pitch is a limit set by the product, not an opinion.
Do not rely on a roofer's memory of a pitch figure, or on a general rule of thumb. Ask to see the maker's sheet for the tile, and ask what pitch your roof measures.
When replacing a few tiles on an existing roof, the question is usually settled, since the old tile was presumably laid within its limits. It matters most when changing the tile type or building something new.
Measuring your roof and checking
The pitch of a roof can be measured in several ways. Plans and elevation drawings often state it. In the loft, a spirit level and a tape measure give the rise over a known run, from which the angle follows. A pitch-finding app on a phone, held against a rafter, gives a quick reading.
At the survey we measure the pitch ourselves, with the equipment for the job, and note it with the other roof details. For a change of tile type, we compare the measured pitch with the data sheet before we quote.
When the roof is close to a limit, there is little margin. A tile used right at its minimum depends on everything else being right: the laps, the underlay, the fixings and the exposure of the site.
If your roof is a shallow one, tell us. It affects which coverings are suitable. Our page on changing to a different type of roof tile sets out the other checks that go with a change of covering.
What you receive is one total covering the work we recommend. The pitched roofing hub covers the other coverings we handle across Farnborough and the surrounding towns.
