Condition ratings
Felt on a small rear flat roof is blistered and the ceiling under it was dry. What rating has that scene earned?
Not quite. Blistered felt on a small rear flat roof is a defect in that felt, and a dry ceiling under it does not choose the number. Dry plaster on the day only says no drip was showing then. The blisters still need the surveyor's own judgement of how serious the felt is. Do not read a dry ceiling as a pass, and do not promote every blister to the most severe mark without their words.
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?
Blisters in felt are the covering ageing or losing its bond, usually on a small flat roof over a rear extension or a bay. The ceiling underneath is a different element. A dry ceiling on the day of the visit means the surveyor saw no active drip and no fresh stain at that moment. It does not mean the felt is rating 1, which is the mark for no repair currently needed beyond normal maintenance. Nor does every blister automatically become rating 3. Rating 3 is serious, urgent, or both. Rating 2 is a repair or replacement that is needed but is not serious or urgent. The surveyor has to say which of those fits this felt.
Flat-roof timbers and the deck under the felt are concealed. No survey level guarantees that those concealed parts are sound, and a dry ceiling is not that guarantee. If they could not see the deck, do not invent a pass for it. Where the felt is rating 3, the what to do now note tells you, the buyer, to get written quotations before legal commitment. It does not invoice the seller, and it does not tell you the dry ceiling has cancelled the blisters. Ask a roofing contractor to judge the felt you can see, and keep any opening-up of the deck as a further step only if the decision needs it.
What should you ask your surveyor?
- Which rating did you give the blistered felt, and why?
- Does the dry ceiling have a separate mark from the felt?
- Were the deck and the timbers under the felt seen, or are they outside this rating?
What are the typical next steps?
- Read the felt rating and the ceiling sentence as two lines.
- Do not treat a dry ceiling as proof the flat roof has passed.
- If the felt is rating 3, get written quotations before you commit.
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
If the blisters are old and stable, can the felt still be rating 2?
Yes, if the surveyor judges that a repair is needed but it is not serious or urgent. Age of the blister is their call.
Does a mineral-felt roof share the rating of the main pitched covering?
No. A small rear flat roof is its own covering. Do not copy the slate or tile number onto it.