Leasehold
The balcony deck was not lifted and the membrane under the boards was not seen. What waterproofing is unknown?
The waterproofing under the balcony boards is unknown. The deck was not lifted, so the membrane that should sit beneath the boards was not seen. Boards can look even, stained, or newly laid, and none of those faces shows the layer that keeps water out of the structure below. The survey has recorded that the deck stayed down and the membrane stayed hidden. It has not tested the waterproofing, and it has not decided that the balcony is watertight. Unknown means the membrane itself was not inspected.
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 balcony deck is the walking surface. The membrane, if there is one, is the waterproof layer under it, turned up at walls and outlets. Water that passes a worn board, a failed joint or a blocked outlet can reach that layer, and damage can show in the soffit or the room below. The surveyor who does not lift the boards cannot say the membrane is continuous, lapped, or even present. A visual note of the boards is not that look. No sample of the layer was taken.
Tell the solicitor the balcony waterproofing is uninspected, and ask who repairs balconies under the lease and whether any guarantee or drawing exists for this deck. A specialist can lift boards under a separate instruction if you need the membrane described. Do not treat a dry soffit on the day as a test of the hidden layer. The survey has not classified the balcony covering, and it has not produced a warranty for it.
What should you ask your surveyor?
- Did you lift any balcony boards, or did the deck stay down?
- What of the membrane, outlets and upstands could you not see?
- Have you left the waterproofing unknown rather than sound?
What are the typical next steps?
- Treat the balcony waterproofing as unknown because the deck was not lifted.
- Ask the solicitor who repairs the balcony and whether any guarantee exists.
- Do not read a tidy deck as a membrane that was seen.
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
If the boards look even and new, has the membrane been inspected?
No. Even new boards are the deck, not the membrane. The deck was not lifted, so the layer under them was not seen. A fresh surface can hide a failed lap or a missing upstand. The survey has not inspected that waterproofing, and a neat finish does not stand in for the lift.
Does a dry soffit below prove the hidden waterproofing?
No. A dry soffit on the day of the visit shows that face was dry then. It does not show the membrane, because the boards were not lifted. Water can sit in the build-up without staining the soffit yet. The waterproofing under the deck remains unknown.