Roofs and flat roofs
Why can a dormer leak while the main tiles still look even?
A dormer is a box built through the slope. Its cheeks, its flashings and its little flat or pitched top fail on their own. Even tiles on the main roof do not speak for those joints. From the street you mostly see the front of the dormer, not the lead or felt where it meets the tiles.
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?
Surveyors look for cracked cheeks, tired felt on the top, and flashings that have lifted. Inside, the stain is often on the side of the dormer or on the ceiling just below it, which people then blame on the whole covering. A visual survey from the ground, and a look from the loft if it is safe, still may not see the top of a dormer. The report should say so.
RICS describes home surveys as inspections, not as a guarantee of the roof. Asking a roofer to “check the dormers” is a different instruction from a quote to retile the house. If the rating is about one dormer, keep the price conversation on that dormer until someone has seen the cheeks and the top. Costs vary with access and with whether scaffold is needed. Do not invent a figure from the rating.
What should you ask your surveyor?
- Did you see the top and the cheeks, or only the face from the street?
- Is the staining inside on the dormer, or under the main slope?
- Are you rating the dormer separately from the tiles?
What are the typical next steps?
- Photograph the stain and the outside of the dormer before any repair.
- Do not accept a full re-roof quote that starts from a dormer cheek.
- If you need certainty, ask a roofer to inspect that dormer and to say what they could not see.
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 roof window the same as a dormer?
No. A roof window sits in the slope. A dormer is a structure with its own walls and top. They leak at different joints.
Does a loft conversion certificate prove the dormer is dry?
Building-control paperwork is about the work as approved, not about today’s felt. The survey looks at condition now.