Cavity wall insulation DIY small job - advise please.

Hello,
me again..
My BCO was keen that I insulate cavity wall (part integral garage conversion) if its not already filled with rockwall (its not).

I'm teraced and this wall in question is the party wall, it only petrudes say 2metres out and beyond my neighboors, so really its only this section that needs cavity insulation. Some builders recon I may get away with it if the BCO is happy with the rest of the work.

I've seen DIY kits (£200+), are there any simple spray injection cans I can buy, one builder even recommended gap filler and just drill holes into wall and blast away. Could this cause thermal briding (even damp) in later years? the house is already half cavity insulated so wouldn't be worth any of these other insulation companies coming out for such small job.

any info as always much appreciated.
KS

i guess insulating from the inside will mean having to do the whole wall?

is this section of wall full cavity, i.e. 75-100mm? this would translate to an overall wall thickness of between 270 -300mm.

hello noseall,
It's more like 50mm cavity, built in the mid 80s.
Thanks
KS

If you use expanded foam cans, then there is a great risk of dampness crossing the cavity. If the external face is sheltered, then the risk is low.

Easiest option is to insulate internally (dry-line).

Easier still is to just tell the BCO you've done it, and make it look like you have.

Or knock out a hole about 700 square, and shove some insulation in with a stick. Use fibreglass not Rockwool as this will just crumble to bits

Thanks Woody, its given me some ideas. With my garage conversion the window will be the width of the garage door opening so I'm trying not to add say another 50mm celotex or other insulation to that wall as it will encroach even closer to the edge of the window, every bit of space counts, the overall width of the grage isn't that wide as it is.
KS

..
Nearly at the stage when I need to do this job. I'm not too sure what checks the BCO can carry out, or if he ever would when it comes to sign off and this cavity wall + insulation.
I got a load of wickes (celotex) boards which I was going to use between the rafters, but now I'm going for standard insulation above joists and closing the roof space in this small mini loft I call it. I may well open up at a later stage.
I'm debating with myself to dot n dab these celotex boards to the wall then more adhesive to back it with plasterboard, rather than spend more ££ on kingspan insulation backed pb.

Woody, (thx for all advise so far onthis project..!) If you read this and could spare a mo, would you recon they would ever check if I use 30,40,50mm celotex.. What I'm afraid is that if I pose the exact question to BCO and he comes up and requests say 70-80mm stuff, then I've shot myself in the foot.
better fit something 40-50mm celotex and keep it at that?
ta
KS