Roofs and flat roofs
What is the difference between an interlocking concrete tile and a clay plain tile?
An interlocking concrete tile is a large single-lap tile that overlaps its neighbours with shaped edges. A clay plain tile is smaller, usually laid in a double lap, and it needs a steeper pitch and more tiles to cover the same slope. A surveyor who names the covering is telling you how the roof is built, not how many years it has left.
Last reviewed 24 October 2026. Written for buyers in England and Wales unless this answer says otherwise. No named surveyor has signed this page. It is general guidance, not a report on your house, and not legal advice.
What is the fuller explanation?
The covering changes what “a few slipped tiles” means. One slipped interlocking tile can open a larger hole than one small plain tile, but plain tiles rely on each course overlapping the next, so a slipped nib or a tired batten can let water past even when the roof still looks tidy from the road. A visual survey sees the surface from the ground, or from a ladder only if that was safe and agreed. It does not strip a patch to see the battens.
RICS home surveys describe condition. They do not publish a life in years for either tile. Moss, lamination and uneven courses are comments about what was visible. Ask which covering is on the house, which slopes were seen, and which were hidden by height, a neighbour’s land or a valley.
What should you ask your surveyor?
- Which covering is on each slope, and which slopes could you see?
- Are you commenting on the tiles only, or also on the lines of the battens?
- What would a roofer need to see that you could not see from the ground?
What are the typical next steps?
- Do not replace a whole slope because one tile is cracked, unless a roofer who has been up there says the rest match that crack.
- Ask the seller whether any slope has been recovered, and keep the invoice with the survey.
- If a valley or an abutment was not visible, say that in any question you send back to the firm.
Costs vary with the building and with who you instruct. Where this page does not cite a published figure, ask the surveyor, a relevant specialist, or your solicitor for a written quote. Do not treat a forum average as the price.
Also asked about this
Are concrete tiles always heavier than the old slates under them?
Often a concrete recovery is heavier than a thin slate roof it replaced. The survey cannot prove the timbers were checked for that weight unless it says so. Ask.
Does a matching spare tile mean the roof is sound?
No. A stack of spares in the loft is useful. It is not an inspection of the laps.