Roofs and flat roofs
What is roof spread, and how is it different from a crack caused by the ground?
Roof spread is the feet of the rafters pushing the tops of the walls outward because the roof is not tied well enough. The clues are at the eaves: walls bowing out, a gap at the ceiling line, sometimes a hump in the ridge. That is not the same pattern as subsidence, which shows at the base and around openings.
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?
Older roofs rely on collars and binders, and sometimes on the ceiling joists, to stop the rafters spreading. If those ties are missing, cut for a loft room, or rotted, the eaves move. A surveyor in the loft can see cut timbers if the loft is safe to enter. From outside they may see a bow limited to the top of the wall. Approved Document A is about structural work that needs building regulations. It is not a calculation the survey has already run.
The Association of British Insurers describes subsidence as a downward movement of the ground affecting the foundations. Roof spread is a roof problem that loads the walls. Mixing the words leads people to underpin a house that needs a structural carpenter. If the report mentions spread, ask what was seen in the loft and whether a structural engineer should look before you commit. Do not take a ground-works price from a roof sentence.
What should you ask your surveyor?
- Did you see cut or missing ties in the loft, or only a bow outside?
- Is the movement at the eaves, or at the base of the wall?
- Are you recommending a structural engineer, a roofer, or both?
What are the typical next steps?
- Do not cut more timbers out to “open up the loft” while this is unresolved.
- Ask for the loft notes: what was tied, what was cut, what was not seen.
- If the walls have moved, a structural engineer should say whether the roof needs restraining. That is not a damp quote.
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
Can a loft conversion cause spread?
It can, if ties were removed and not replaced with another design. The survey cannot prove the calculations. Ask for the building-control papers and what timbers are there now.
Is a bowed eave always roof spread?
No. Wall-tie failure and rotten plates can bow a wall too. The height of the bow and the loft timbers are how you start to tell them apart.