Age and type of house

Original steel windows meet a rotten timber sub-sill. Which of those materials has the rating actually described?

Both, but only as seen, and they should not be blurred into one material. The steel window and the rotten timber sub-sill are different. The surveyor can describe rust on the metal, failed putty, and rot in the timber under the frame. They have not tested the window as a product and have not opened the wall below the sill. Original steel is not a defect merely for being original. The rotten timber is the piece that needs the repair comment.

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 1930s steel window often sits on a timber sub-sill, with a concrete or tiled outer sill beyond it. Water gets trapped at the junction. The metal can be painted and still thin. The timber can be soft while the steel looks crisp. A single rating that says 'windows' hides which one you would actually pay to repair. The visit looks, probes where already open, and notes flaking. It does not remove the frame, and a standard inspection does not take off secured fittings. Putty and paint are not a laboratory test of the steel thickness.

Ask the report to say metal and timber in separate words if it has not. An empty cavity behind the jamb, if this is a cavity house, is not itself a defect and was not proved by a rotten sill. Do not replace every steel window because one sub-sill is soft, and do not keep a rotten sill because the metal is original and attractive. Rating 2 is repair that is not serious or urgent. Rating 3 is serious or urgent. The sill's softness is what should drive that choice, described at the windows where it was found.

What should you ask your surveyor?

Did you find rot in the timber sub-sill, rust in the steel, or both, and at which windows?
Was the wall below the sill opened, or is the comment limited to the visible faces?
Are the two materials written separately so a repairer can see which one failed?

What are the typical next steps?

Point a joiner at the rotten timber and do not assume every steel frame must go.
Do not treat original steel as a defect just because it is original.
If several sills are soft, get quotes before you commit if the rating says the repair is urgent.

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 new owner have to replace steel windows to satisfy the survey?

Only if the report says the metal itself needs repair or replacement. Original metal in fair condition is not automatically a defect.

Is the rotten sub-sill the same element as the outer tile sill?

No. Tile, concrete, timber and steel should be named. Rot in timber does not rate the tile by itself.