Roofs and flat roofs
What should you ask if the flashing around a pipe through the roof looks split or blobbed with mastic?
Ask about that pipe only. A soil vent or another pipe through the covering needs a collar or a proper flashing, and a split collar or a blob of mastic is a local rain path, not a valley failure and not an abutment. The survey sees the outside of the pipe if it was visible, does not camera the pipe, and does not pass the rest of the slope.
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?
Pipes move slightly and mastic hardens and falls out. The durable detail is a flashing that laps the pipe and the covering. A temporary smear can look tidy on completion day and open later. From the ground you may only see a dark ring or a stain on the ceiling beside the pipe. A home survey should say whether the collar was seen, guessed, or hidden on the far slope. It will not dismantle the flashing.
The pipe itself may be a drainage or ventilation pipe. The survey has not tested the drain and has not flow-tested the stack. Keep the weatherproofing comment separate from any smell or slow gulley. A roofer prices the collar. A drainage firm, if you need one, prices the pipe. There is no single figure that covers both. Do not reroof because one vent penetration looks tired.
What should you ask your surveyor?
- Which pipes pass through the covering, and which flashings did you see?
- Is the defect a split collar, mastic, or a stain you could not trace?
- Are you excluding a drain test?
What are the typical next steps?
- Ask a roofer to quote the pipe flashing on its own.
- Do not seal a soil pipe with mastic and call the survey closed.
- If the loft is stained only beside that pipe, say so. Do not blame the whole slope.
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 boiler flue through the roof the same detail?
The weatherproofing question is similar. The flue is also an appliance path the survey does not safety-test. Keep those sentences apart.
Does a new plastic pipe mean the flashing is new?
No. Pipes are replaced without the flashing being redone. Ask what was seen at the covering.