Basements and cellars
What should you ask about a lightwell drain outside a basement window?
Ask whether the gully was seen and where it goes. A lightwell is a hole in the ground against the wall. If its drain blocks, the hole fills and the window sits in a pond. That is penetrating damp from outside, not a mysterious failure of a damp-proof course inside. The survey can see leaves in a gully. It does not rod the pipe.
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?
Basement windows and their wells are a classic leak. The seal around the frame, the cill and the drain have to work together. A survey from inside sees the stain. A survey from outside may not enter a small well safely. The report should say which view it had.
Clearing a gully is not the same as proving the drain beyond it. If the rating says water has entered, ask a drainage firm to look at this outlet, not only at the kitchen stack. There is no RICS price for lightwell drainage. Do not use the England flood map as a substitute. GOV.UK says that map does not cover blocked drains.
What should you ask your surveyor?
- Could you see the bottom of the lightwell?
- Is there a gully, and was it blocked?
- Is the staining at the window or on the opposite wall?
What are the typical next steps?
- Photograph the well before anyone hoses it out.
- Get a quote that includes the drain, not only new glass.
- Do not tank the inside wall and leave the well blocked.
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 lightwell a flood zone?
No. It is a local hole that fills if its own drain fails. The flood map is a different document.
Can you cover the well with a grille and forget it?
A grille keeps feet out. It also collects leaves. It is not a drainage design.