Age and type of house
A purlin is cut where a dormer cheek was formed. Has a calculation for that cut been seen?
No calculation for that cut has been seen. A purlin helps carry the rafters, and cutting it where a dormer cheek was formed interrupts that line. The survey recorded the cut where it could be seen. It has not seen a structural calculation, a design for how the load was picked up, or a building-regulations approval for the alteration. The visit has not decided the cut is adequate because the dormer is still standing.
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?
When a purlin is severed, the load it carried has to go somewhere else: into a trimmer, a beam, or a remaining length that was never meant to work alone. None of those alternatives is proved by the fact of a finished plaster cheek. The survey can see the end of the timber and any obvious sag nearby. It cannot invent the calculation that should have justified the cut. Standing up today is not that arithmetic.
Ask the solicitor for any building-regulations certificate, engineer's calculation or completion record for the dormer, and keep the absence of those papers in view. The survey does not issue a building-regulations certificate. A structural engineer can assess the cut if you instruct that. Do not tell a lender the roof alteration was checked by calculation. The report only confirms the purlin is cut and that no calculation was in the papers seen.
What should you ask your surveyor?
- Was the cut purlin recorded without a calculation beside it?
- What alternative support, if any, was actually visible?
- Are building-regulations papers for the dormer missing from the pack?
What are the typical next steps?
- Treat the cut as seen and the calculation as not seen.
- Ask the solicitor for any approval or engineer's design.
- Do not describe the standing dormer as proof the cut is adequate.
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 steel beam nearby count as the missing calculation?
Only if the papers show it was designed for this cut, which they have not. A beam in the room may carry something else entirely. The survey can note a beam it sees. It cannot treat that beam as the calculation, or as proof the purlin load was picked up, without the design.
Can the surveyor calculate the load after the visit from photographs?
No. Photographs show the cut that was visible. They are not a structural design, and this survey has not calculated the load. A later engineer, properly instructed, would need to inspect and design. Do not ask the home survey to become that calculation after the event.