It can, but it isn't automatically the culprit. In walls exposed to wind-driven rain, or where the outer brickwork, pointing or render is defective, insulation can help water cross the cavity, and gaps in the fill can create cold spots for condensation. The cause needs proper investigation before anything is removed.
Cavity wall insulation has made a lot of homes warmer. It has also caused problems in houses that were never suitable for it or where the job wasn’t done well. Both of those things are true, and the trick is working out which applies to your house.
How CWI can lead to damp
A cavity wall has two leaves of masonry with a gap between them. The original idea was that any rain soaking through the outer leaf would run down the inside of the outer leaf and drain out at the bottom, never reaching the inner wall. Fill that gap with insulation and, in the wrong circumstances, water can be carried across to the inner leaf. That’s more likely where:
- The wall faces the prevailing wind and gets heavy wind-driven rain.
- The outer brickwork, pointing or render is in poor condition and letting water in.
- Gutters and downpipes are leaking onto the wall.
- The cavity already had debris, mortar droppings or other bridges in it.
Patchy or incomplete fill can also leave cold spots on the inside face of the wall, where condensation and mould form in a pattern that doesn’t match the rest of the room.
How to tell
Damp that appears or worsens after rain, on the exposed side of the house, at any height, points towards rain penetration. Isolated patches of mould on the inner face of an external wall can point towards cold spots from gaps in the insulation. A thermal camera, a borescope inspection through a small hole and a look at the outside of the wall all help.
Just because damp appeared after insulation went in doesn’t prove the insulation caused it. New windows, blocked vents, or a change in how the house is used can all happen around the same time.
What to do
- Fix the outside first: gutters, pointing, render, sills and cracks.
- Find your CWI paperwork. Many installations carry a guarantee, often through CIGA, and you should contact the installer or guarantee provider if you think it’s at fault.
- Get an independent assessment before agreeing to extraction. Removing insulation is sometimes the right answer, but it should be based on evidence.
When to call a specialist
If you suspect your cavity wall insulation is causing damp, get an independent survey that looks at the wall, the insulation and the weather exposure before making a claim or paying for extraction. Book a survey with All Dry on 01226 287181 or email info@alldrydampproofing.com.
Listen on The Damp Show
Frequently asked questions
Can cavity wall insulation be removed?
Yes, it can be extracted, but that should only follow a proper assessment of the cause.
Who guarantees cavity wall insulation?
Many installations carry a guarantee, often through CIGA, so check your paperwork.
Is damp after CWI always caused by the insulation?
No, external defects, ventilation changes and leaks can all cause similar symptoms.