Wall ties and cavity insulation
What does the Energy Saving Trust say should be repaired before cavity insulation is installed?
The Trust’s cavity-wall advice, updated 8 May 2026, says defects should be repaired first, including damaged brickwork or pointing, roofs and gutters. It also says not to insulate while internal walls are damp, and that very narrow or rubble-filled cavities, and walls exposed to driving rain or flood, may be unsuitable.
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?
The same page says a typical installation in Great Britain can cost around £2,200, and around £1,000 in Northern Ireland. That is the Trust’s published typical figure, not a quote for this house and not a repair cost for a defect in your survey. Suitability still depends on the wall in front of you.
A home survey is not an insulation survey. If it has found open pointing, a failed gutter or a damp patch, those are reasons to pause before anyone pumps material into the cavity. The Trust says a good installer should not block ventilation. Ask the installer to confirm that in writing. If ties are also suspect, deal with the investigation of the ties before you fill the cavity and hide them.
What should you ask your surveyor?
- Which defects in your report would you want repaired before any cavity was filled?
- Did you see vents or underfloor grilles that insulation must not block?
- Are you able to say the cavity is wide enough? A visual survey usually cannot measure it.
What are the typical next steps?
- Use the Trust’s figure only as context. Ask an installer for a price after they have assessed this wall.
- Repair the rainwater and the brickwork the survey actually named before you talk about filling the cavity.
- If the house is already filled, ask for the paperwork rather than a new price.
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 the Trust say insulation never causes damp?
It says insulation should not cause damp if the wall is suitable and the job is done properly, and it tells you to contact the installer and check any CIGA guarantee if damp appears afterwards. It does not say every existing installation is dry.
Is the Great Britain figure valid in Northern Ireland?
No. The same page gives a different typical figure for Northern Ireland, around £1,000. Neither figure is this house.