This is literally the worst case of wet insulation I have ever come across. Also highlights don’t presume you know what the problem is, it’s not always that simple!

A property owners recently had cavity wall insulation installed to keep their property nice and warm and cozy………

A few months later  severe mould appeared to the under stairs cupboard and also along the stringer of the stairs on the first floor.

We were called in for a damp survey, to be fair I thought the problem would be the insulation just because the house has been fine for years, bit of insulation injected and we have a problem.

On pulling up on the drive it was evident how damp the wall was, it was visibly damp stained.

Externally there was a possible defect with the guttering that had a small leak tracking back against the wall.


I proceeded to drill the cavity to carry out a boroscope inspection, for the first time ever in my life water span off the drill bit onto my hand….wow this wall is soaked.


The boroscope didn’t really show anything as the wall was stuffed full of insulation, I had to remove a brick.

The below picture just shows how wet the wall is there, there was water on the damp proof course.


Blown fibre insulation could be scrunched up it was so wet.


On removing the insulation we find a 15mm pipe dripping in the cavity.


We take a brick out further up the wall cut the pipe of with a pipe slice and stick a tube on so we can try to get the water to run away from the building. The pipe is traced back to the airing cupboard on the first floor, this is something to do with the pressure release valve, and also should have been in copper.


We decided to remove the plasterboard internally, to include the ceiling under the stairs to investigate for timber decay, fortunately this was ok. Removal of the cavity wall insulation and drying of the structure before re-instatement works.


We carried out the whole job from survey, report, drying, all repairs, and dealt with the insurance company.

This was an interesting survey, which I thought would make a nice case study as everybody was blaming the insulation. Damp surveying is an art, and the surveyor has to be prepared to spend time on a survey, and normally open up areas to find the actual cause. If I hadn’t opened up we would have blamed the small gutter leak and the cavity wall insulation.

I will post some more case studies of recent jobs actually because of wet cavity wall insulation from penetrating damp.


Posted by Complete Preservation


  1. as informative as ever, great post. keep em coming


  2. I think we could have damp problems because of cavity wall insulation. We have mould and the plaster is coming away, the house was built in 1970 with a damp proof in the wall. Not sure if you remember, you fixed my aunties house in Marlborough where there were all the fish skeletons under the floor.


    1. Hi Tracey,

      I can remember you and Mary 🙂
      I’m sure the heron got the blame for stealing the fish, but it was the rats lol


  3. Good work Ross as ever, assume nothin. Colin King


    1. Hi Colin,
      Exactly assume nothing 🙂


  4. Ross I spoke to a few weeks ago about you looking the damp walls. Really like a survey this week please.

    Bill Griffin


    1. Hi Bill, give me a ring tomorrow


  5. How do we book a survey? We have had a free cavity wall insulation damp survey and they have said that the mould in our bunglalow is because of the insulation and it all needs to be removed. One area is protected so it can’t be getting wet. I like what you do as it seems more of an investigation rather than a quote.


  6. Awesome! Thanks for sharing.


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