Wall ties and cavity insulation
Why do people say wall ties should be dealt with before a cavity is filled?
Because insulation blown or injected into a cavity can hide the ties and can sit against a wall that is already cracking or bridged. The Energy Saving Trust says the masonry should be in good condition, the cavity at least 50mm and clear of rubble, and repairs to pointing, roofs and gutters done first. A home survey does not carry out that pre-install check for you.
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?
Filling a cavity is an alteration, not a survey finding. If ties are failing, the outer leaf needs restraint, and insulation in the way makes a later inspection harder. The Trust also warns against filling walls exposed to driving rain or in poor condition, because of damp. Those are suitability tests, not a diagnosis that your wall has failed.
If the report mentions both insulation and ties, keep them in order: structure and rainwater goods first, fill second, and only if the cavity is suitable. Do not accept an insulation grant quote that ignores a bow the surveyor has already described. The survey fee does not include the installer’s survey.
What should you ask your surveyor?
- Has the cavity already been filled, or is fill only being suggested?
- Did you see a bow or bed-joint cracks that filling would hide?
- Are you saying the wall is unsuitable, or that you could not see the cavity?
What are the typical next steps?
- Do not book cavity fill to “solve” a tie crack.
- If fill is already there, tell any tie firm. They need to know before they drill.
- Ask the installer for the suitability checks in writing. The Trust’s page is the list, not your house’s certificate.
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 filled insulation cause tie failure?
The rust is a metal and moisture problem. Fill does not invent it, but it can hide it and it is a poor idea on a wall that is already failing.
Is 50mm a rule for every house?
It is the Trust’s suitability figure for ordinary cavity insulation. It is not a measurement the surveyor took unless they say they did.