Roofs and flat roofs
The loft notes damp on the underside of the sarking and the tiles outside are whole. Why might that be condensation in the roof build-up rather than a leak?
It might be condensation in the roof build-up because the tiles outside are whole and the damp is on the underside of the sarking, which is where moisture in the roof space can settle. BRE has described dripping that is built-up condensation rather than a leak through the covering. Whole tiles do not prove that account, but they do mean a hole in the covering was not what the survey saw. The inspection recorded damp on the sarking. It has not proved a leak, it has not proved condensation, and it has not run a test that separates the two.
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?
Sarking felt is the layer under the tiles. In cold weather the air in a loft can drop moisture on that cold sheet, and the drips then look like a leak even though the tiles are intact. That is the pattern BRE has described when a roof appears to drip from the build-up rather than from rain coming through a gap. The survey can put the two observations side by side: damp underneath, covering whole outside. It cannot, from one visit, decide which mechanism produced the damp it noted.
Do not invent a home test to force an answer. Tell the solicitor the report leaves both possibilities open, with no failed tile identified. A roofer can look at ventilation and at the felt, and can say whether anything in the covering still needs repair. The survey has not specified new tiles and has not said the felt must be stripped. If you need the two causes separated, that is a further look, not a conclusion this note already reached. Leave the sarking in place.
What should you ask your surveyor?
- Where was the sarking damp, and were the tiles over that area whole?
- Did you see a hole in the covering, or only damp on the underside?
- Have you left leak and condensation as undecided?
What are the typical next steps?
- Read damp sarking under whole tiles as undecided, not as a proved leak.
- Ask a roofer to look at ventilation as well as the covering.
- Do not strip the tiles on this note alone.
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Also asked about this
If drips fall in summer, does that prove a leak?
Not from the season alone. The survey still saw whole tiles and damp on the underside, and it has not run a test that separates condensation from a leak. Timing of a drip was not established as rain entry. The home survey itself did not pursue this summerdrip question any further than the visit.
Does whole tilework mean the felt can be ignored?
No. The damp is on the sarking, so the felt is part of the note. Whole tiles mean a covering hole was not seen. They do not mean the underside damp can be ignored. No later decision about the sarkingfelt was made, and this visit did not supply one.