Roofs and flat roofs
The only outlet sits in the middle of a pond. Has that outlet been proved blocked?
The outlet has not been proved blocked. The only outlet sits in the middle of a pond on the roof, which shows water standing around it. Standing water can mean the outlet is high, slow, blocked or simply sitting in a hollow in the deck. The survey saw the pond. It did not rod the outlet, lift the covering or run a controlled test. Ponding is the defect that was visible. A blockage is one possible cause, and it has not been proved.
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?
A flat roof should fall toward an outlet so water leaves. When the only outlet is in the middle of a pond, water is not getting away. Debris in the outlet is a common suspect, and so is a badly laid deck that ponds even when the outlet is clear. Those causes look alike from a surface inspection. Proving a blockage means clearing or rodding and seeing the flow. Nobody did that. The report should stay with the pond, not jump to a named obstruction.
Ask the seller when the roof was last cleared and whether the pond is permanent. A roofing contractor can rod the outlet and check the falls. That is not this survey. Tell a lender there is ponding around the only outlet and that a blockage was not proved. Do not authorise a full strip of the roof on the blockage theory alone. Get the outlet checked first, and keep the covering unopened until a contractor needs to go further.
What should you ask your surveyor?
- Has the outlet been rodded to prove a blockage?
- Can a hollow deck pond even if the outlet is clear?
- Was the covering lifted around the pond?
What are the typical next steps?
- Treat ponding as seen, and a blockage as unproved.
- Ask the seller when the outlet was last cleared.
- Instruct a roofer to rod the outlet and check the falls.
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
Can the pond be caused by levels rather than debris?
Yes. If the deck falls toward a low spot and the outlet is not at the true low point, water sits even when the outlet is open. The survey did not rod the outlet and did not take a long series of levels. Debris remains possible. Levels remain possible. Neither cause has been proved. The visible fact is the pond around the only outlet.
Was the deck opened under the pond on this visit?
No. The covering stayed in place. Ponding was a surface observation. The deck, the insulation and any wet boards underneath were not exposed. Opening the roof would be a contractor's work, instructed separately. The survey has not called the structure under the pond rotten or sound. It has recorded the water lying at the outlet.