Roofs and flat roofs
A truss web was cut to make room for a water tank and no extra timber was seen. What of that truss joint is now missing?
The web that was cut is the missing part of that truss joint. A truss web is a member that joins the others and shares the load. Cutting it for a water tank removes that member at the joint, and no extra timber was seen to replace what the cut took away. The survey has recorded the cut and the absence of additional timber. It has not calculated the strength left in the truss, and it has not designed a repair. The tank sits where the web was. The joint lacks the piece that was cut, with nothing seen in its place.
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?
Roof trusses work as frameworks. Each web gives the forces a path. When a web is cut to squeeze a tank in, that path is broken at the joint the web used to meet. Extra timber, a gusset, or a designed frame around the tank might put a path back, and none of that was seen. The surveyor looked and recorded the gap. They did not test the truss and they did not measure how far it has moved. Missing timber is the observation. A structural design is not.
Ask a structural engineer to say how this truss should be repaired or supplemented, before the tank is relied on. Tell the solicitor a web was cut and no extra timber was seen, so the support is not confirmed. Any building-regulations approval for the alteration is a paper to ask the seller for. The survey has not produced that approval and has not designed the replacement member. Do not pack the cut with an offcut and call the joint restored.
What should you ask your surveyor?
- Which truss web was cut, and for which tank?
- Was no extra timber seen at that joint?
- Has the strength of the truss been left uncalculated?
What are the typical next steps?
- Treat the cut web as a missing part of the truss joint.
- Ask an engineer how the joint should be put back.
- Ask the solicitor for any approval of the alteration.
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
If the ceiling below is level, has the truss coped?
A level ceiling on the day is not a calculation. The web was cut and no extra timber was seen, so that part of the joint is missing. The survey has not measured strength and has not said the truss has coped. Ceilings can stay level for a time and still sit under a cut member.
Can the tank stay if a piece of timber is simply added beside the cut?
The survey has not designed that repair. No extra timber was seen, and the cut web is what the joint is missing. Adding a piece without an engineer's design is not the report saying the joint is restored. Ask the engineer what member is required. Do not invent the repair from the fact that a gap was recorded.