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Roofs and flat roofs

What should you ask if a roof truss has been cut to make a loft room?

Ask whether the cut is supported, and do not assume the new bedroom has building-regulations approval. Trussed rafters work as a set of timbers. Cutting one changes the roof. A home survey can see a cut member and a boarded room. It does not design a beam, and it does not sign the work off under Approved Document A.

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?

Approved Document A is England’s structural guidance when building work is done. Wales has its own regulations. A visual survey is neither approval. The clues are a severed diagonal, a missing piece, or a trimmer the surveyor cannot see because it is boarded. Papers, if they exist, are for the solicitor. An indemnity policy does not hold the roof up.

If you plan to use the room as a bedroom, the structure, the stairs and the fire separation may all matter. The survey describes what is visible. There is no RICS price for putting a truss back or for a new floor. Ask an engineer or a building surveyor instructed for that alteration, not for a repaint.

What should you ask your surveyor?

  • Which members were cut, and which were hidden by boarding?
  • Did you see a supporting beam, or only a plasterboard room?
  • Are you saying the roof is unsafe, or that the alteration was not proved?

What are the typical next steps?

  1. Ask the solicitor for building-regulations papers for the loft room.
  2. Do not cut any further timber.
  3. If the rating says the structure is unclear, get advice before you rely on the room.

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 cut in an old purlin roof the same thing?

No. Older cut roofs and factory trusses work differently. The survey should say which roof this is.

Does a velux window mean the trusses were cut?

Not always. Some openings are trimmed properly. The survey should say what it could see, not guess from the window.

Sources