Minimum tile pitch
What is the minimum pitch for roof tiles?
The short answer
It depends on the tile. Marley's published minimums start at 15 degrees, for its Lincoln clay pantile and the smooth Mendip concrete tile, and rise through 17.5 degrees for several interlocking concrete tiles, to 35 degrees for concrete plain tiles and 30 to 40 degrees for clay plain tiles. BS 5534 indicates 20 degrees for 500 mm natural slate in moderate exposure. Always read the data sheet for your own product.
What minimum pitch means, the figures for common tiles and slate, and why a low-pitched roof needs more care than the number alone suggests.
What a minimum pitch is for
Pitch describes how steeply a roof slopes, measured in degrees up from the horizontal. Each tile and slate has a lowest angle at which it keeps weather out. Below that angle, wind can drive rain up beneath the laps, or the water may run off too slowly to clear them, and the covering leaks however well it is nailed. The figure comes from the maker and, for slate, from BS 5534.
The minimum can also shift with exposure and with the finish of the tile. The same product may carry a higher minimum on an exposed site, and a different one for a smooth face than for a textured face. So a general number is only a starting point. The product data sheet is the document to check, and any roofer ought to produce the sheet for the tile named on your quote. Ask for the pitch to be written on the survey too, so the two can be checked against each other.
Figures for common clay and concrete tiles
Marley's guide to the minimum pitch for a roof tile or slate gives the following. Among clay plain tiles, Canterbury needs 40 degrees, Ashdowne 35, and Hawkins and the Acme Single Camber 30. Its Lincoln clay pantile goes right down to 15, which is why a pantile, the S-shaped clay tile, suits a shallow slope. A concrete plain tile needs 35 degrees.
Interlocking concrete tiles go lower. Edgemere, and Modern and Duo in the smooth finish, are 17.5 degrees. Double Roman in smooth is 22.5, as are Ludlow Major in smooth, Ludlow Plus and Ashmore, while Anglia in smooth is 25. Mendip in smooth and Wessex are both 15, and Mendip 12.5 manages 12.5 degrees, as its name suggests. Each figure belongs to a named product, not to a tile type in general, so a similar-looking tile from another maker can differ and must be checked against its own sheet.
Slate and the fixings that go with it
For natural slate, Cupa Pizarras says BS 5534:2014+A2:2018 indicates a minimum pitch of 20 degrees, for a 500 mm slate in moderate exposure. At 20 degrees, a 500 by 300 slate laid in sheltered or moderate exposure is given a headlap of 115 mm. Headlap is the distance each course reaches down over the course beneath it, and it is the main defence against water creeping up under the slates.
Cupa adds that hook fixings should not go on any pitch below 25 degrees. So a slate roof at the low end needs a different fixing from one on a steeper slope, a detail that is easy to miss on a quote. For the coverings themselves, our page on roof tile types compares the main choices, and the interlocking and plain tile answer shows why their minimums differ so widely.
Low pitches and the pull of the wind
A shallow roof is not only a rain problem. Marley warns that on slopes under 30 degrees the windward side can be subjected to severe suction, also called negative pressure. That lifts tiles instead of pressing them down, so fixings on a low roof have to be chosen for the site, not copied from a steeper one.
Wienerberger says the right fixing specification turns on geographic location and on altitude and local wind exposure. A tile that meets its minimum pitch still needs the correct nails or clips for where the house stands. Near the sea, where gales are part of the weather, that is worth confirming with the roofer before the order goes in. If you are changing the covering on an existing roof, the other checks, on the condition of the battens and underlay, come first.
Finding your pitch, and what to do if it is too low
The pitch of your roof is rarely written down anywhere. A roofer can measure it with a digital level at the eaves, or in the loft along a rafter, and a survey records it. A phone app held against a rafter gives a rough reading, but it is not a basis for choosing a tile or ordering materials, and the error can be several degrees. Measure in more than one place, since an old roof may have settled and the slope can vary along its length.
If your pitch is under the minimum for the tile you want, there are three ways forward. Choose a tile with a lower minimum, such as a pantile or one of the low-pitch interlocking ranges. Raise the pitch by altering the structure, which is a larger job and may need Building Regulations approval. Or use a different kind of covering altogether. Turning a flat extension roof into a sloping one is a case in point, covered on our flat to pitched roof page, and the pitched roofing hub lists the rest of our work.
Related questions
Pitch questions
Can I lay concrete plain tiles on a roof of 25 degrees?
No. Marley's minimum for concrete plain tiles is 35 degrees, so 25 is too low. An interlocking tile with a lower minimum would suit that slope, and the maker's data sheet confirms which ones do.
Does a steeper roof always last longer?
Not by itself. A steeper slope sheds water sooner and loads the laps less, but fixing, underlay and upkeep matter more to how long a roof lasts. Pitch decides which coverings are allowed, not how long they survive.