Roofs and flat roofs
An open joint in a parapet coping lets you see daylight and the felt field below is dry. What path does rain have through that joint?
Rain has a path through the open joint in the parapet coping, down into the parapet and towards the wall beneath, even though the felt field below is dry. Daylight through the joint shows the coping units no longer close. Water does not need a wet felt field to use that gap. It can enter the head of the parapet and track inside the wall. The survey has recorded the open joint and a dry field. It has not traced a leak into a room, and it has not repointed the coping. The path is the joint you can see through.
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?
Copings shed rain off the top of a parapet. The joints between coping units are part of that cover. An open joint is a slot. Rain driven at it, or simply falling into it, enters the top of the wall rather than the felt on the roof below. A dry felt field means the surveyor did not see that field failing. It does not seal the coping. The two surfaces are different. Daylight shows the joint is open. It is not a forecast of how much rain will enter.
Ask a bricklayer or a roofer to close that coping joint, and to check the damp course under the coping if they open the area. Tell the solicitor the felt field was dry, so the note is a path through the parapet joint, not a failed felt roof. The survey has not said a room is already wet. Leaving the joint open keeps the path, whatever the felt is doing. Do not reseal the felt and ignore the coping.
What should you ask your surveyor?
- Which coping joint is open enough to show daylight?
- Is the rain path through that joint, with the felt field dry?
- Was any leak into a room left untraced?
What are the typical next steps?
- Treat the open coping joint as the rain path.
- Do not call the dry felt field the failure.
- Ask for the joint to be closed before you blame the flat roof.
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 no stain shows inside, is the joint only cosmetic?
No. Daylight through a coping joint is an open path for rain into the parapet, whether or not a room is stained today. The felt field being dry does not close the joint. The survey has not traced a leak inside, and that absence is not a finding that the slot does not matter. Rain still has that path when it falls on the coping.
Should the felt be stripped because the coping joint is open?
Not from this note. The felt field below is dry. The path is the open joint in the parapet coping. Stripping a dry field would be a different decision, and the survey has not made it. Close the joint that shows daylight. Do not turn a coping slot into a full roof renewal the report did not describe.