Roofs and flat roofs
What should you ask if mortar debris is sitting in a roof valley, even when the lead looks whole?
Ask whether the lining is split or the valley is simply dammed by broken mortar from a ridge, a hip or a verge, which can hold water even when the lead is intact. That is a blockage, not proof the metal has failed. From the ground the debris is often invisible, and a loft stain under the valley still does not show you the lead.
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?
Valleys collect whatever falls into them. A repointed ridge can shed lumps of mortar that no one clears. Water then overtops the lining and wets the boards or the ceiling, which reads like a split valley when the sheet is whole. Clearing debris is a different job from relining the valley. A home survey should not upgrade a blockage into a failed lead valley unless a split was actually seen.
The limitation is access. A standard inspection does not walk every valley and does not lift the tiles along it. If the surveyor could not see into the valley, the honest sentence is that it was not seen, not that it passed. Ask for the loft comment under that line as well as the outside comment. There is no set price for clearing a valley. A roofer who can see it should separate debris from a hole in the lining.
What should you ask your surveyor?
- Did you see debris in the valley, a split in the lining, or neither?
- Was the valley visible from the ground, from the loft, or not at all?
- Would clearing the channel be enough, on what you saw, or do you think the lining is open?
What are the typical next steps?
- Do not commission a new lead valley because mortar has fallen into the old one, unless someone has seen a split.
- Ask the roofer to say whether they found debris, a hole, or both.
- Keep the valley comment separate from the tiles on either side.
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
Is mortar in a valley the same as a mortar-bedded ridge?
No. Ridge bedding is the joint on the ridge. Debris is that material, or verge mortar, lying where water should run.
Can underlay show you the blockage?
No. Underlay, if you can see it, may be stained. The blockage is outside, in the valley channel.