Cavity wall insulation

Hi all!
I was trying to measure the width of the cavity in the outer walls of our 1930s semi to work out if cavity wall insulation is possible - by opening up an air brick vent low down in our lounge (seems to be about 70mm but hard to be accurate).

While I was doing that some fluffy white material fell out - anyone know what this is?
Is this an old form of cavity wall insulation perhaps? If so, does that mean there’s not much point in having it re-insulated?

Finally, could it have asbestos in it??

Many thanks


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Hi Peter,
I can answer part of that.

I believe it is cavity wall insulation. We have the same in our 1980s bungalow. We’ve had a corner of the bungalow opened up to add an exrension and this stuff was in it

Does it gave asbestos? Don’t know, our builder didn’t panic so I’m hoping not.

I dont like this type because it is blown in, very light and Ivv bc suspect a lot of friction. They found air pockets on the corner which is irritating to think there may be gaps elsewhere.

I most likely means your cavity is filled, so if you want more insulation you need to do internal or external. My knowledge ends there I’m afraid.

great thanks Robin - very useful :slight_smile:

Interesting photo! Have you got another photo looking more directly into that hole?

Looks like knauf supafil to me, which is what we have in our cavities. And yes the installers do tend to miss bits.

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I’m glad you didn’t lose your phone in there. I’d be tempted to pack that space with mineral wool before covering it over again. It looks reasonably dry in there too so I am not sure whether the air vent was really needed? Can you feel at draft in there when you put your hand in? Does (or did) the room have a gas fire in it or an open fire? Do you still want / need a fire in the room? If no fire then the need for air from this location may no longer be important.
In terms of passive inlet vents the Aereco vents are probably the best. You would probably fit one of those Aereco units higher up, say 1.9-2.0m above floor level.