Yes, in most cases you can. Cavity wall insulation is common in UK homes, and on its own it rarely stops a mortgage. It becomes a problem when the lender's valuer or your own surveyor spots damp, mould or other signs that the insulation may have failed. Then the lender may ask for a specialist report, hold back part of the loan, or want the problem put right first.
This post covers what lenders look for, the paperwork to ask the seller for, the checks you can make on a viewing and what happens if the insulation needs to come out. You can look for warning signs yourself, but never drill into or open up a wall in a house you don't own. Finding out what is inside the cavity is a job for a specialist.
Why cavity wall insulation alone is rarely a problem
A cavity wall is two layers of brick or block with a gap between them. Most UK homes built between the 1920s and 1990 have them. Millions were insulated later by blowing insulation into the gap through small holes drilled in the mortar.
Most of those installations cause no trouble. Welsh Government guidance says most were done in suitable homes to a good standard. A lender's valuer is mainly checking that the house is worth what you are paying and is sound security for the loan, so insulation in good order rarely changes their view.
When a lender looks harder
Lenders tend to become cautious when:
the valuation or survey notes damp patches, mould or staining on the inside of outside walls
the walls face the worst of the weather, where wind-driven rain can soak the outer wall and cross the cavity on wet insulation
nobody can show what was installed, when or by whom
work has been done on the walls with no paperwork to prove it
In those cases the lender may ask for a specialist cavity wall inspection, or a report confirming the insulation isn't causing problems, before it releases the money.
What a mortgage retention means
A retention is when the lender holds back part of the loan until named work is done and signed off. It is usually triggered by something the valuer has seen. For you, it means either paying for the work yourself after you move in, or agreeing with the seller that it is done before completion. Terms vary between lenders, so ask your mortgage adviser exactly what yours needs to see.
The paperwork to ask the seller for
Ask your solicitor to request:
the cavity wall insulation guarantee, often a 25-year guarantee from CIGA, the Cavity Insulation Guarantee Agency
the installer's name and the date the work was done
any certificates or reports if insulation was removed or wall ties were replaced
Welsh Government guidance says a large share of guarantees in Wales are held by CIGA, and CIGA can check whether one was issued for a particular home. If it has no record, another guarantee provider may hold one. Our guide to how cavity wall insulation guarantees and CIGA claims work explains what a guarantee covers.
Checks you can make on a viewing
You can look for these without touching anything:
small, evenly spaced filled holes in the mortar across the outside walls, a common sign the cavity was filled after the house was built
damp patches, mould or flaking paint on the inside of outside walls, especially low down, around windows and in corners
one wall that feels noticeably colder than the rest of the room
outside brickwork that looks wet or stained, or leaking gutters and cracked render that let rain soak in
None of these proves the insulation has failed. Condensation, leaking gutters and plumbing leaks leave similar marks. They are reasons to ask more questions. Autumn and winter viewings are a good time to look, because walls are at their wettest. Our post on how to tell if a house has cavity wall insulation goes into more detail.
Why your survey may not give the full answer
A HomeBuyer survey or a full building survey is a visual inspection. The surveyor won't drill into the walls, so they can report signs of trouble but usually can't see the insulation itself.
If your survey flags a concern, a specialist cavity inspection is the next step. The specialist looks into the cavity through a small hole using a borescope, which is a small camera on a flexible tube. They check what the insulation is, whether it is wet or has slumped, and the condition of the wall ties, the metal ties that hold the two layers of the wall together. Ask the seller's permission first, because the house is theirs until completion.
If the insulation needs to come out
If a specialist finds failed insulation, you have choices before you exchange contracts. You can ask the seller to have it removed, renegotiate the price to cover the work, or check whether a valid guarantee covers it.
Removal isn't always the right answer, and Welsh Government guidance recommends professional advice before deciding. Where it is needed, the insulation is drawn out with specialist extraction equipment, the cavity is cleaned and the access holes are made good. With the cavity open, it is also the right moment to check the wall ties through a wall tie survey.
