Roofs and flat roofs
The extension's flat roof is ponding and the survey saw it from a bedroom window. Has the deck been opened?
The deck has not been opened. The extension's flat roof is ponding, and that pond was seen from a bedroom window, which is a view of the surface only. Ponding shows water lying on the covering. It does not show the deck, the insulation or the boards beneath, and the covering was not cut. The survey has not decided whether the structure under the pond is wet, decayed or still sound. The limit is the window viewpoint and the unopened roof.
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?
Water that stands on a flat roof loads the covering and finds any lap or crack. From a bedroom window the surveyor can see the shine and the extent, and still cannot feel the deck or look underneath. A window view is not a ladder on the extension and not a core through the membrane. The joists of an extension roof can decay under a pond while the ceiling below looks ordinary. None of that hidden zone was opened. The pond is the finding. The deck is the unknown.
Ask the seller how long the pond has sat there after rain. A roofing contractor can get onto the extension, check the outlet and open the deck only if that is justified. The survey has not authorised opening-up and has not condemned the joists. Tell a lender the flat roof ponds and was seen from a window, with the deck unopened. Do not describe the structure as rotten, and do not describe it as dry. The covering was not lifted.
What should you ask your surveyor?
- Was the deck of the extension roof opened?
- Is the ponding note based on a view from a bedroom window?
- Has the structure under the covering been called decayed or sound?
What are the typical next steps?
- Treat the pond as a surface view, not an opened deck.
- Ask the seller whether the water sits after every rainfall.
- Instruct a roofer onto the roof if the deck must be known.
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
Does a bedroom window show whether the insulation is wet?
No. Glass gives a view of the top surface and the pond. Insulation sits under the covering and was not exposed. Wet or dry insulation cannot be judged from the bedroom. The survey did not cut the roof. The ponding is real as a surface defect. The layers below remain unseen and untested.
Is ponding itself proof the joists have decayed?
No. Ponding is a reason to worry about the deck, not proof the joists have gone. Decay needs moisture in the timber over time, and that timber was not seen. The covering was not opened. Some ponding roofs still have sound boards, and some do not. This survey has not sorted which. The window view cannot do that sorting.