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.

Hello I am in Sheffield so out of your main area.
I have a 3 bed semi 1930 with single story extension built 16 year ago that goes around most of side of house and wraps around half of the back of the house. Seems this extension is our first issue for installing cavity insulation.
Installer I just spoke to checked out property on google maps whilst I was on the phone and said as well as the extension there may be issue as well as the Headabricks- rectangle bricks -something about decorative or going into the property making it unsuitable for cavity wall and a question about gable wall running all the way around.
I understood the basics of this but if you can help at all on whether that makes sense and if you can suggest any installers who cover Sheffield.
We have done some internal insulating and also considered external cladding.
Be glad of some help
Many thanks
I would be very grateful

You could insulate the cavity in sections if there is an interrupted cavity but you will end up with thermal bridges between the sections. There is little point in external wall insulation if you have an empty cavity as your slightly warmer cavity will simple vent into the roof or straight out. Internal insulation has thermal bridges between rooms, both at internal walls and between ceilings and floors, although it is sometimes possible to insulate between storeys.

It would seem that in your case a combination approach is required. As I am not in, or even near, Sheffield I can’t suggest a company but bear in mind that they will need to be PAS 2035/2030 registered. Alternately get a whole house assessment by a retrofit coordinator and get the components done as time and budget permit.

Personally I would do CWI followed at a later date by EWI, assuming that your house is suitable for EWI.

I don’t see how you can have a gable wall forming more than a triangle at the top of the house. That is more or less the definition of “Gable Wall”. Please explain more about your roof and the gable end, so that I and others can better contemplate your insulation requirements / predicaments. A photo might be useful.

Hi Mike. Apologies for resurrecting an old thread. Did you have any luck finding an installer?

Hi Tom. Yes I finally went for Cooney, based in east Mcr ; I think they did a good job, hard to know for sure, obvs. The installer (Nathan) showed me how the injection thingy worked. He asked about air vents - you need to identify these and specify which ones you want to be kept open. (Most of them.) We had ‘step cracks’ in the mortar of the bricks, in a couple of places, which he re-pointed - you can press the installer to do some extra re-pointing… Price seemed fair enough, £1,600 for our semi-detached.