Windows, doors and glazing
Why does it matter if a balcony door threshold falls back towards the room?
Rain on the balcony then runs towards the floor inside instead of out onto the balcony, so the fall of that threshold is the point. It is not a window cill that slopes back to the glass, and it is not a door set below the outside paving. A home survey can see the fall if the door was opened and the balcony was in view, it does not hose-test the door, and a dry day is not proof the fall is outward.
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 doors fail quietly. The frame can be firm and the glass clear while the threshold tilts the wrong way, so water tracks under the door and into the screed or the timber. A visual survey looks at the level, the seal and any stain on the inside floor. It does not take the threshold out. Fitted flooring may hide the damage already done. Not lifting finishes is a normal limit. A stain just inside the door is a clue, not a measured depth of water.
The repair may be the threshold, the balcony outlet, or both. A blocked balcony outlet can push water at a threshold that would otherwise have been fine, so ask the surveyor which they saw. There is no standard price. Do not replace the door leaf because the fall is inward unless the leaf itself has failed. Do not treat this as a window-cill job. If the balcony structure was only seen from inside, the deck and its outlet may be not inspected rather than satisfactory.
What should you ask your surveyor?
- Does the threshold fall outwards or back into the room?
- Was the balcony outlet visible, and was it blocked?
- Is there staining inside the door, or only the fall?
What are the typical next steps?
- Show a joiner or a roofer the fall and the balcony outlet together.
- Do not replace the whole door until someone has checked the threshold.
- Do not confuse this with the paving level at a ground-floor door.
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 level threshold the same fault?
A level threshold has little margin. The survey should say whether water can still run out, not only whether it visibly runs in.
Does a new uPVC door prove the fall?
No. New frames are set at whatever fall the opening had. Age of the door is not the slope.