Cavity Insulation Recommend?

Has anyone had a good cavity-wall insulation job done by a firm they can recommend? Anywhere near-ish Gorton/Longsight/Levenshulme area. Thanks!


Hi Mike, welcome to the Carbon Co-op community. Sorry that this message got a little lost, on our end we have been quite busy and there have been a lot of people on holiday. I added your thread to the #home-retrofit category, which will hopefully help more people with experience in this area see it, and I will ask around our team to see if there is anyone who has a better idea!

Welcome to the forum @mike_killian . I don’t live in your area so cannot answer your question but do have some advice on cavity wall insulation.

Find out all you can about the different types of cavity insulation and their properties. Also consider how porous your walls are and how exposed to driven rain you might be. If the inner leaf of your walls are permeable are you likely to get warm air penetrating the wall into the cavity and the humidity condensing out against the outer leaf.

Now consider what the most appropriate type(s) of insulation are.

Now look for a supplier of that/those type(s).

Don’t rely on the supplier’s survey. Guess what, your walls will be ideally suited to the type of insulation that they supply.

Thanks Tim. Was considering the cavity-beads method. We’re not exposed to driving rain. I’ve not considered permeability of inner walls, so I suppose a separately-done survey would answer that? I had thought of doing a separate/independent before-n-after thermal-radiation survey - or, getting the installer to agree to same - so we can see what the immediate difference is. However, that would be after-the-fact, and wouldn’t expose potential permeability problems arising later…

Thermal surveys are easiest and therefore cheapest in midwinter, preferably before dawn. If you want a “before” you won’t be getting an install until rather too late in the heating season.

Vapour permeability of the inner leaf isn’t a problem providing you have appropriate measures in place, ie. free draining, non capillary, inert insulation.

Air permeability is another matter and should be addressed urgently. You may need a blower door test to discover the failing areas. A combined airtightness and thermal survey should do the trick.

You could take the method approved by AECB, or their chairman Andy Simmonds. That is to use closed cell foam. That creates an airtight & vapour tight layer within the structure of the wall. Your airtightness will leap up as your wall U value plummets, exceeded only by the balance of your savings. The justification for using an oil derivative is that it rapidly saves more than was used in its production and keeps on doing so.

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Thanks Tim. I was thinking of a chilly autumn-winter early-morning for a ‘before’ survey, for the reasons you say. I had thought foam was considered less-good than beads because it’s more difficult to ensure homogenous/even distribution of foam (plus, it’s more-awkward to undo/remove, in the event of problems.) But the final problem is, how to find a reliable contractor - it’s quite a big thing to ask someone to stuff the walls of your house with some substance… which is why I haven’t done it, over 12 years of being here.

Generally I agree with you. I did have regular (open pore) foam insulation added to my then house in the late ‘70s and when I changed the windows there were no gaps visible. Also the foam protruded from the top of the cavity in the loft.
The difference with Andy Simmond’s case is that he specifies closed cell. This makes an airtight, water tight, vapour impermeable and it’s much more expensive. You won’t get cold or damp bridging and don’t need to worry about future airtightness measures. Being waterproof you won’t get damp from exposed walls transferring inside.

What you might have to do is introduce MVHR to maintain air quality.

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Do you mean, you were expecting to see some spacing/gaps, to allow a level of breathability within the insulation, but you saw no such gaps or spacing?

Certainly not! I was responding to this:

I was indicating that there was no evidence of gaps, not that I wanted any.
Open cell foam is slightly permeable. So the building can breathe very slowly and likewise damp can transfer from one side to the other, so not suitable for all walls/locations.

Oh right, got that… Thanks.