Roofs and flat roofs
Tennis balls and leaves are stuffed in the secret gutter behind a parapet. What lining under that debris was not seen, and where would an overflow wet the wall?
The lining under the tennis balls and leaves was not seen, and an overflow would wet the wall beneath the parapet. Debris stuffed in the secret gutter hides the sole and the outlets. Water that cannot get away spills onto the wall the parapet is meant to protect, often at the head of that wall rather than as a missing tile on the slope. The survey has recorded the blockage it could see. It has not cleared the gutter or proved the wall is already wet.
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?
A secret gutter is a channel you barely see from the ground, tucked behind the parapet. Its lining, whether metal or felt, only shows once the channel is empty. Tennis balls and leaves sit on top of that lining and can also sit in the outlet. The survey could not see through them. An overflow path is down the back of the parapet and into the wall head, which is why stains sometimes appear inside at the top of the room rather than halfway down a tile slope.
Ask a roofer to clear the secret gutter and then report on the lining and the outlets, with the seller's agreement. Keep that separate from the home survey. Tell the solicitor the finding is a blocked channel whose lining was hidden, not a cleared roof. If there is already staining inside at the wall head, show the roofer that mark. Do not read the survey as having inspected the lining.
What should you ask your surveyor?
- Was the lining of the secret gutter hidden by the debris?
- Where would an overflow from that blocked channel wet the wall?
- Did you leave the gutter uncleared, with the outlets unseen?
What are the typical next steps?
- Treat the secret gutter as blocked and its lining unseen.
- Ask a roofer to clear it and then report on the lining.
- Link any high-level internal stain to that overflow path.
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 tiles in front of the parapet look sound, is the gutter fine?
No. Sound tiles on the slope do not show the channel behind the parapet. The tennis balls and leaves still hid the lining. The survey has not cleared that gutter or seen the sole. The weather detail that matters is the blocked secret gutter, not the tiles in front of it.
Does moss on the parapet prove the wall is already saturated?
Not on its own. Moss shows a damp surface that holds growth. It does not measure water inside the wall, and the survey did not open the wall head. The certain note is the blocked gutter. An overflow would wet the wall beneath the parapet, but that wetting was not proved by moss.