Is cavity wall insulation frowned upon?

Expanding foam cavity fill can be added to cavities with rusting cavity ties to hold the two skins together.

Mike

There are allegedly some dramatic damp problems due to fitting it in the wrong sort of situation, or with the wrong sort of householder. In Merthyr Tydfyl and points south especially, for some reason. I don't know the truth of the matter.

It keeps elephants out

My wife's SIL bought a bungalow a couple of years ago that had cavity wall insulation, (don't know the age of the bungalow, but maybe

OTOH my late mother had urea-formaldehyde foam injected into her 1960 bungalow cavity walls circa 1975 which appears OK; no sign of damp. I always understood that U-F foam had a limited life, and went brittle with age, and certainly the 'balloons' of foam that came up the cavity into the loft space were brittle. But we've recently had a door cut through what used to be an outside wall with a cavity, and where the cavity is exposed, the foam has more the texture of cotton wool than foam, and is in perfectly good condition with no brittleness.

Depends on the house etc.

Some houses, including ours, were build with it as standard. We've not had a problem.

The issues Roger refer to relate to the 'injected' stuff which, if not correctly done, can cause problems related to damp.

If it was done correctly, then there should be an issue. If not, there may be. The uncertainly is knowing if it was done correctly. I suspect this sometimes comes down to the reputation of the company if there hasn't been an issue. Obviously, if there are signs of problems, there will be queries re the quality of the work.

Interestingly, cavity insulation has been around longer than some people think. I recall seeing some houses built over 50 years back and one of the foreman explaining to my father how they placed the insulation in the cavity. It was polystyrene sheet.

Well if it is working then its fine I imagine. I suspect they have a legacy thing going on. In the beginning they used chemicals that could cause headaches and funny smells and some installers did not really know what they were doing and made damp issues worse by bridging cavities with 'stuff'. I've not heard any really scary stories recently though. I'd love to have cavity wall insulation here, but sadly we do not have cavity walls in this terrace and in order to do anything really meaningful it really would need all occupiers to have something done. Brian

I think I need to have underfloor insulation and one of my Chimneys is making plasstic flapping noises so I guess its that time again to find a bloke who can fit a chimney balloon, on the other hand of course I could just buy a cheap roll of bubblewrap and shove it up the hole with the end of a broom?

Brian

There was a problem with fibrous insulation blown into the cavity. When this got wet for whatever reason (rising damp, falling damp, leaks, condensation on the inner surface of the outer brick skin) it made the fibres stick together and heavier, and they tended to sink. In the end, a mass of soaking wet insulation ended up at the bottom of the cavity. That caused the ties to rust quickly, and severe mould problems on the inner wall.

I understand that it can be removed with powerful vacuum machines, and there are companies which specialise in this.

Even polystyrene balls can be an issue if they aren't used properly. Everyone always finds a few balls coming out when a hole is drilled into the cavity, but when we had new patio doors fitted the stuff just poured out when the old doors were removed. I'd always though that when blown in a weak adhesive solution was used at the same time to make the balls stick together. But not, apparently, in our place!

No - it's a +ve. It does work - limited to how wide the cavity is.

Some of the foam stuff injected in the 70s was notorious for causing illness due to the fumes, but even that will have gassed off long ago.

The only negatives that I know of:

2) The blown fibre can settle - mine did a bit, but not so much that'd you'd worry - it still works.

If I ever got our place redone, I would opt for either foam or glue lined balls.

When it's installed during the build, it's normally held against the inner skin, leaving an air gap against the outer skin, and that prevents moisture wicking through.

Someone in the road had polystyrene balls installed some 30 years ago. A few months afterwards, the tail-end of a hurricane passed over, and the whole street and all the gardens were full of polystyrene balls for months. I presume they blew out the tops of the cavities.

Depends on property. Possibly not a good idea if a property is likely to be subject to much driving rain.

Drivel. Full fill cavity wall "bats" are moisture repellent mineral wool. As is the stuff blown into existing walls. Damp patches can appear due to cement droppings on fishtail cavity wall ties.

Rigid insulation board is secured against the inner leaf with clips attached to the cavity wall ties during construction.

Our 70's bungalow is similar - with U.F foam installed soon after it was built. We've now made several large holes in the outside walls for major alterations, and the foam is soft but still fills the cavity completely - no apparent slumping or other changes. No apparent damp problems either, despite being fully in contact with the outer leaf.

It appears to be a good long-term product - provided you are not having to breathe the formaldehyde gas during the initial period after installation!

Charles F

We're on the north coast of Scotland - driving rain with gale force winds is the reason we haven't had insulation pumped into the wall cavity. What we have is insulation-backed plasterboard - with that, double-glazing, and tight-fitting doors and windows, the house stays nice and warm.

You are reading too much into the question.

The Bellway houses built near me in 2010 had one-inch thick eps sheets chucked inside the cavities.

I knew this when 2 years ago one house had a 2 story extension and the original cavity wall was broken into, showing these eps slabs just lying in the middile of the cavity, all skew-wiff not even carefully lined up like lego bricks so that the cold air could just pass on both sides of the insulation. So as an insulant, it was utterly useless.

You can do a new-build with full-fill rockwool cavity batts but that requires the brickie to be careful not to allow mortar to lie on top of a line of batts before the next row is added.

It is treated to repel water, so nothing should cross the cavity, though I wouldn't be happy with full-fill if I lived on the South Coast, or West coast of Wales or Cumbria and parts of Western Scotland.

A new build with a 100mm cavity, with 50mm celotex, where the slabs are carefully cut, butted and taped and held firmly to the inner leaf with special round clips on the wall ties should be weather proof even in the most severe locations.