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Can cavity wall insulation be topped up or refilled?

Posted by Tasha Kosviner on 9 June 2014 at 10:10 am

Q: We had cavity wall insulation pumped into out walls about 30 years ago. Over the last 10 years or so it has been shedding the beads through air-bricks and any holes drilled in the walls to such an extent that I now question it's efficacy. Is it possible to have it refilled?

A: The short answer is that yes, you can, and you should, get your walls re-insulated. If your insulation is failing, as it sounds as though it is, you will begin to get cold patches on your walls that will render your home less energy efficient. Research has shown that a five per cent gap in insulation will account for 50 per cent of your home's heat loss. It will also eventually lead to condensation building up creating patches of mould on your internal walls. 

Unfortunately, since your insulation is over 25 years old, it will no longer be under guarantee with the Cavity Insulation Guarantee Agency and you will need to cover the work yourself. 

Tim Pullen, author of The Sustainable Building Bible, has this advice:

"It sounds as though your beads have settled and you should refill your cavity from the top," he says. 

To do this, Tim says, you or your contractor will need to get access to the top of the cavity or to drill holes along the top of the wall and take a look inside. Once he has ascertained how far your insulation has fallen, he will then be able to refill your cavity either by pouring the beads into the top of blowing them in through the holes.

With respect to your air bricks, you could also get these taken out now, as a cavity wall that has been insulated is no longer in need of ventilation. This is now standard practice when insulating cavity walls.

More information

YouGen guide to cavity wall insulation

Does cavity wall insulation cause damp?

Photo Credit: harry harris via Compfight cc

If you have a question about anything in the above blog, please ask it in the comments section below.

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2 comments - read them below or add one

Nigel Donohue

Nigel DonohueComment left on: 26 March 2019 at 8:46 pm

This is incredibly poor advice from Tim Pullen.


Firstly Airbricks are absolutely essential if you have suspended foorboards with a gap beneath them. The airbricks provide ventilation which stops the timbers from rotting. So well done Tim. Block them up and not only would you be violating building regulations but causing a massive bill to the home owner when their floorboards rot away.

Now a cavity was designed to have ventilation so that small amounts of moisture vapour can escape and Cavity vents help facilitate that. We are told they can be blocked up if the cavity is insulated because the insulation sould stop any air flow thought the cavity anyway.

Secondly topping up is not covered by BBA certificate and is not going to be covered by a CIGA guarante. 

>>Unfortunately, since your insulation is over 25 years old, it will no longer be under guarantee with the Cavity Insulation Guarantee Agency and you will need to cover the work yourself.

Does the author really think that CIGA would have covered that work if it was in gurantee?  The CIGA guaranteee is not worth the paper its written on but in this case you have said that you have distrubed the insulation by drilling holes - that invalidates the guarantee because of course it is unreasonable for a home owner to do any holes in a hole over 25 years.

The final point is why on earth are the beads coming out of the air bricks? the subfloor vents should be protected by a sleeve or second best a cavity brush which keeps the insulation out and so should never leak though the air brick - the install wasnt done properly and if you have suspended floor the beads are blocking the insulation and could very well have ended up under your floor boards.  This is typical of the poor quality installs that were done in the gold rush of CWI where unskilled installers didn't do proper surveys or checks.

avoid CWI.



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alfComment left on: 13 February 2015 at 5:16 pm

My problem is the rentokill fibre seems to be losing its insulation after 25 years and I have found a few bits where it is missing. Can I get this fixed?


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