Roofs and flat roofs
What should you ask if a cement fillet has been used where a roof meets a wall, instead of lead?
Ask whether that junction is mortar rather than metal. A cement fillet is a triangular band of mortar used instead of soakers and a cover flashing, and it cracks and parts from the wall so water can run behind it while the tiles still look even. A home survey sees the fillet if it is in view and cannot see how far water has tracked.
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?
Mortar is rigid and the roof moves. The fillet opens at the wall or along the tiles, often in a crack you can see from the ground, sometimes only after rain. Lead or another proper flashing is chased or lapped so water stays on the face. A fillet has no lap once it cracks. Calling it an abutment flashing hides the fact that the usual metal detail is missing. The survey should name what is there.
Raking out a fillet and fitting a flashing is a local job at that wall, not a new roof, unless the tiles under the fillet are also gone. There is no standard price. If the junction is behind a parapet or above a bay, say so, because access changes the work. Do not inject the wall for rising damp because the stain starts under a fillet. The path is from the junction down.
What should you ask your surveyor?
- Is the junction a cement fillet, lead, or something you could not see?
- Is the fillet cracked, or only a different material from the one you would expect?
- Did you see staining below it, inside or outside?
What are the typical next steps?
- Ask a roofer to price a flashing at that abutment, not a whole-slope re-cover, unless they find more.
- Do not repoint the fillet and call it a flashing.
- Photograph the crack at the wall if you can see it from a safe place.
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 a neat fillet acceptable because it looks fresh?
Fresh mortar can still be the wrong detail. New does not mean it is chased metal. Ask what was used.
Does a fillet at a chimney differ from one at a dormer?
The material point is the same. The access and the flashing length are not. Keep each junction separate.