New builds and warranties
The balcony deck on a new flat looks dry. Has the inspection seen the waterproofing layer beneath it?
No. Standing on the balcony shows you the surface, the upstands you can see, and any ponding or damage on top. The waterproofing membrane underneath is concealed. A dry day is not a test of that membrane, and a warranty is not a substitute for the limit of the inspection.
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?
Balcony leaks often sit in the build-up, at the door threshold, or where the covering meets the wall, not in a neat stain in the middle of the deck. The surveyor can comment on falls, cracks, open joints and staining to the underside if they can see the underside from this flat. They cannot see through the finishes. NHBC’s Buildmark is a 10-year warranty and insurance: the builder is responsible for the first two years, and NHBC guarantees that, and the following eight years insure damage from defects in specific parts, not every snag. That does not make the hidden membrane visible.
Do not write that the membrane has passed. Do not write that it has failed unless there is evidence. If the underside is stained, say what was seen and ask who should investigate. A snagging list that says balcony OK because the tiles look new has gone further than the inspection. There is no RICS tool in a standard survey that peels a new balcony back to the membrane.
What should you ask your surveyor?
- What of the balcony was visible, from above and from below?
- Are you silent on the membrane itself?
- Did a dry surface get written up as a test?
What are the typical next steps?
- Describe only the surface and the underside you could see.
- Ask the builder for the balcony waterproofing detail if the papers should hold it.
- Do not treat Buildmark as a visual check of a concealed layer.
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 flat below has a stain, is that this membrane?
It may be related. It is not proof by itself, and this survey may not even have entered the flat below.
Does a new covering mean the membrane is new?
Not necessarily. The survey cannot date a layer it cannot see.