Roofs and flat roofs
Drips fall from the underside of the roofing felt and the tiles above look even. Why might that be built-up condensation rather than a tile leak?
Those drips might be built-up condensation rather than a tile leak, which is a distinction BRE has described. Moisture from the rooms can gather on the cold underside of roofing felt and fall in drips while the tiles above still sit even, with no slipped or missing piece to point at. The survey has recorded drips from the felt and an even tile line. It has not proved condensation, and it has not proved a leak. It has not set out a test that would decide between them. Even tiles make a simple hole in the covering less obvious.
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?
Built-up condensation is moisture that air in a cold roof drops onto a cold surface, here the underside of the felt, until it runs and drips. A tile leak is rain coming through from outside. Even tiles do not rule a leak out, because water can track from a detail you cannot see, but they do remove the obvious displaced tile. BRE has described dripping that is built-up condensation rather than a leak. The survey can point at that possibility. It cannot certify which mechanism this roof is using.
Tell the solicitor the report records drips and even tiles, and that the cause was not proved. If the two must be separated, ask a roofing firm to look at the coverings and at how the roof space is ventilated, as a further inspection. Do not treat this sentence as a test method. BRE's point is that a drip can be misunderstood. The home survey has not stripped tiles and has not measured the air in the loft. Do not reroof from the drip alone.
What should you ask your surveyor?
- Did drips fall from the felt while the tiles looked even?
- Have you left both condensation and a tile leak unproved?
- Did you avoid describing a test the visit did not include?
What are the typical next steps?
- Read the drips as unexplained, with condensation a real possibility.
- Do not assume a tile leak from a line of even tiles.
- Ask a roofer to separate the causes if you need a decided answer.
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 drip appears only in cold weather, is it certainly condensation?
Cold weather fits condensation, and BRE has described drips that are built-up condensation rather than a leak. That does not prove this roof. The survey saw drips and even tiles and did not run a test. Rain and cold can arrive together. The mechanism in this house remains unproved either way.
Should the felt be stripped because the underside is wet?
Not on this note. Wet felt is what was seen. The survey has not specified stripping it, and it has not decided the wetness is a leak rather than condensation. BRE's warning is that the drip can be misread. A later inspection can recommend work. This report has not written that specification.