The short answer
Plain tiles are small, flat and laid in rows that overlap by two courses, so water has several layers to cross. Interlocking tiles are larger and lock sideways into each other, which makes them quicker to lay and workable at lower pitches. Plain tiles suit traditional and period roofs; interlocking tiles suit most newer houses and shallow slopes.
How each type is laid on the roof
A plain tile is a small, slightly curved rectangle, and it works by overlapping. Each row, called a course, covers the joints of the course below, and the tails of the tiles sit over the heads of those two rows beneath. Water that gets past one layer meets another. The roof ends up with a fine, even texture that you see on many Victorian and Edwardian houses and on older village buildings.
An interlocking tile is bigger and carries a groove or rib along its side edges, so one tile slots into the next across the row. Only a short overlap at the head is needed from one course to the next. Fewer tiles cover the same area, which is why laying goes faster. Marley's range shows the idea well: the Double Roman, the Mendip and the Ludlow are all interlocking profiles, with the surface running from smooth to deeply profiled.
Both types hang from battens, the timber laths nailed across the rafters. Both rely on underlay beneath, and on clips and nails to hold them in wind.
Weight on the rafters and walls
Weight matters because the rafters and walls were designed around the covering that was put on originally. Marley gives its concrete plain tile as 73.8 kg/m² when laid at a 100 mm gauge, with a 65 mm headlap. That is a useful baseline, though clay plain tiles and interlocking profiles each have their own data sheets, and the tile maker's published figure is the one to use for any particular product.
Changing from one covering to another can change the load. Approved Document A counts a load increase of more than 15 per cent as a significant change, while the Planning Portal asks for approval where a covering is 15 per cent heavier or more. Going from a lighter interlocking tile to heavy plain clay is therefore worth checking before anything is ordered. If the roof might need strengthening, the Planning Portal tells you to get a structural engineer or surveyor involved before starting, and your building control body will want to hear about it.
A like-for-like replacement on an unaltered roof raises none of these questions. The rafters, purlins and wall plates have already carried that weight for years, so the survey is mainly looking for timber that has rotted or sagged since.
Typical cost per m2 for clay and concrete
Plain tiles take longer to lay, so the labour element tends to be higher for the same area. Checkatrade's roof repair guide (updated October 2026, with the table last updated June 2026) gives typical repair costs per m² of £110 to £160 for clay and £90 to £120 for concrete, excluding VAT and excluding access equipment. These are national repair figures for tiled work, not prices for your roof, and a full re-roof is priced differently.
| Covering | Typical repair cost per m² |
|---|---|
| Clay tiles | £110 to £160 |
| Concrete tiles | £90 to £120 |
What moves the figure on a real roof is access, the size of the area, how much of the timber needs renewing and whether a tile has to be sourced to match. After our survey the quote is sent in writing as one total. Whoever quotes you, ask whether the figure includes VAT and scaffolding.
Pitch: where each type can and cannot go
Each tile has a minimum angle of slope, below which wind-driven rain can be pushed up under the laps. For plain tiles the minimums are fairly steep. Marley lists its concrete plain tile at 35 degrees, and its clay plain tiles at 30 to 40 degrees depending on the profile, with the Canterbury at 40.
Interlocking concrete tiles cope with much shallower slopes. In the same Marley table the minimums run from 12.5 degrees for one Mendip tile up to 25 degrees for the Anglia, with many sitting around 15 to 22.5 degrees. Low extension roofs, porches and the sloping sides of dormers are often too flat for plain tiles, and suit an interlocking profile.
The maker's data sheet for the exact tile gives the figure to trust, because it varies from product to product. Our page on the minimum pitch for roof tiles sets the table out in more detail.
Choosing for your house
On a period house, a conservation area or a listed home, the existing covering is part of the character, and plain clay tiles are usually the expected choice. Consent may be needed to change them, and matching an existing roof is a skill in itself. Our page on matching old roof tiles covers that side.
On a 1960s to 1990s estate house, the roof is often interlocking concrete, and replacing like with like is straightforward and sensible. Changing to a different material is possible, but it is a design decision, and our page on changing tiles to slate shows what that involves.
Whichever type you have, a damp loft can be down to poor air flow instead of the tiles; our roof ventilation guide explains what to look for. You end up with survey photographs of the roof itself and a quote on paper, and the finished work carries a 10-year workmanship guarantee, also on paper.
Weighing one tile type against the other for a repair or a whole new roof? Our pitched roofing hub gathers the rest of our tiled roof pages in one place. A snapshot taken from the pavement, plus the approximate age of the house, usually lets us name the family of tile before we visit.