The short answer
Plain tiles are small, flat and double-lapped, giving a finely textured roof that needs a steeper pitch, from 30 to 40 degrees for Marley clay and 35 for its concrete plain. Interlocking tiles are larger, laid in a single lap and locked at the sides, and many suit pitches from 15 to 17.5 degrees. Plain suits older, steeper roofs, while interlocking suits shallower and larger ones.
How the two formats keep water out
A plain tile is a small rectangular tile, traditionally clay, hung from a batten by two nibs and slightly curved across its length. Tiles are laid in overlapping rows so two thicknesses of tile sit over every part of the slope. Roofers call this double-lap, and it takes a great many tiles to cover a roof. The weathering relies on gravity and the steep angle, with each tile lying under the one above.
An interlocking tile is much larger and has a profiled edge, a channel or rib along its side that engages with its neighbour. It is laid in a single lap: the tile overlaps only the course below by a headlap, and the side joints carry the water down their channels. Fewer, bigger tiles cover the roof quicker. Pantiles and double roman profiles are interlocking tiles; both come in clay and concrete.
Pitch: the main practical difference
Because a plain tile relies on double-lap overlap and steepness, its minimum pitch is high. Marley lists its clay Canterbury at 40 degrees, Ashdowne at 35, Hawkins at 30 and its concrete plain tile at 35. Interlocking profiles run lower: Marley's Lincoln clay pantile is 15 degrees, its Mendip concrete tile 15 degrees in smooth form and its Edgemere 17.5. Sandtoft's Old English clay pantile needs 30 degrees.
That gap makes the choice for many roofs. If your slope is 25 degrees, a plain tile is not suitable, while a pantile or interlocking concrete tile may be. If you want to change formats on an existing roof, the pitch must still meet the new tile's minimum, and our answer on the minimum pitch for roof tiles sets out the published numbers. The product data sheet has the last word.
Look, weight and cost
The visual difference is considerable. A plain tile roof has a fine, close grain with a soft, slightly uneven texture, and hand-made clay tiles weather beautifully. Interlocking tiles read as bolder, with strong lines or waves running down the slope, and a larger scale overall.
| Point | Plain tiles | Interlocking tiles |
|---|---|---|
| Laying | Double-lap, many small tiles | Single-lap, fewer large tiles |
| Typical minimum pitch | 30 to 40 degrees for Marley clay, 35 concrete | 15 to 17.5 degrees for many Marley profiles |
| Look | Fine texture | Bold lines or waves |
| Labour | More tiles to fix | Quicker coverage |
Weight and cost vary by product, material and supplier, so we do not quote a general figure. On cost, In Checkatrade's 2026 cost guide, concrete tile repair is £90 to £120 per m² and clay £110 to £160 per m², before VAT and with access extra. These are national ranges, and an itemised quote from us follows the survey, with tile, labour and scaffolding priced apart.
Which suits an older house, and which a newer one
Older houses tend to carry plain tiles on steeper roofs, and the small tiles follow the curves of old timber frames well. Changing to a large interlocking tile on such a roof alters its character and can be a planning matter in a conservation area or a listed building. On an older roof we start from the same format and material the house already has, so plain tiles are replaced with plain and clay with clay.
A middle path exists for people who love the look of plain tiles but have a roof that is too shallow for them: some makers offer a profile that imitates the look of small plain tiles in a larger, interlocking format. It is a different product with its own pitch, weight and fixing rules, so it needs its own data sheet check, and it will not fool a close inspection. We tell you plainly when we think it suits and when it does not.
Newer homes often have interlocking concrete tiles, laid quickly on lower pitches to fit common roof designs. Extensions and shallow porch roofs often need an interlocking tile or a different material because of their pitch. If you are choosing between clay and concrete rather than format, see our guide to roof tile types, and for the pros and cons of matching what is already there, matching old clay tiles.
What changing the format involves
Swapping plain for interlocking is not a like-for-like job. The new tile has a different gauge, headlap and weight, so the battens are usually re-fixed to new spacings, and the roof structure is checked. Where the new covering is 15% heavier or more than the old, Approved Document A calls for a structural check and approval. Our answer on concrete tiles and old roofs covers that rule.
Cost is not the only trade-off. Small plain tiles mean more fixings and more batten lines to get right, so labour is a larger share of the job, while an interlocking roof spends more of its budget on the tiles. Neither is automatically cheaper, and the answer depends on the product you pick and the shape of the roof, with hips and valleys adding cutting time to both.
We survey first, take photographs of your roof and measure the pitch. Our quote then separates access, stripping, new materials, labour and clearance. Where the job needs Building Regulations approval, we explain why and make the notification. A 10-year workmanship guarantee comes in writing with the work, and the roof, drive and gutters are left clear of offcuts. For the full service, see pitched roofing.