Cavity wall Insulation for narrow cavity

[meow2222]

Hi

Cavity wall (brick & block) with a slightly narrow 1.5" cavity, any advice re cavity filling it? What fill, if any, would work with such a cavity? Any tips on diying it?

thanks, NT

[John Rumm]

Do you want to insulate and existing wall, or is this insulating a new one as it is built?

[meow2222]

Its an existing wall, and making holes in it to fill it is no problem.

ta, NT

[John Rumm]

Any of the normal loose blown in or injected cavity wall insulation products then...

[Tim S]

[e-mail] coughed up some electrons that declared:

Mines been done in blown fibre - probably 10-15 years ago. Seems in good condition judging by what I've found after cutting holes in the wall. Also hasn't settled - loads up on top of the cavity.

I've heard good things about poly beads - they coat them with glue now so you don;t drown in white stuff if you make a large new opening down the line.

Cheers

Tim

[meow2222]

I thought most of them needed blowing in, I dont have the equipment. I'd be looking at pour in, and polystyrene bead is the only one I believe that can be done with. Are there any others? Any specific bead size, coating, etc? The issue Tim mentioned of beads pouring out of holes shouldnt be a problem.

NT

[Tim S]

[e-mail] coughed up some electrons that declared:

If it were me, I'd go with the beads if you really want to DIY it. Making some sort of wide channel out of ply or thick cardboard and pouring them on that and using it to direct them over the wall leaf into the cavity might help - I guess there'll be a lot of volume of beads.

Would you be doing this from inside of out?

If I were paying, fibre seems OK, but glued beads might be better from a damp tracking POV (though I've never seen damp in the walls and the outside is unrendered brick).

[meow2222]

inside

the wall is damp, and will stay so, but I cant see poly beads making it worse. I think unglued ones would be an insurance policy though, just in case. I have heard of the odd case where CWI made the damp much worse, and needed to be removed, but IIRC those were from water running down inside the cavity, which doesnt happen in this case.

NT

[meow2222]

I realised something else too, theres a balanced flue duct going through the wall for a 3kW cast iron heater, so almost 3kW going outside through that. Is that compatible with polystyrene bead? I guess I know how to find out.

NT

[Tim S]

[e-mail] coughed up some electrons that declared:

Does it run no more than warm to the touch in the bit you can get at? And is it concentric? Any heat shield where it goes through the wall?

It's not going to take much to melt polystyrene :(