The cavity is obviously well ventilated, the cavity insulation board is not too effective and the inner skin mortar has gaps in it. From what you say it sounds like you have dot and dab plasterboard fixed to the wall - yes?

If the above description sounds like your extension then this would be fairly typical.

A fix would be full fill the cavity with say EPS beads and also consider wet plastering the walls having first removed the plasterboard.

Tony may be along soon to advise on the merits of 'plasterboard tents'

Yes, eps beads can help, they are both vapour open and air open but offer considerable resistance to air movement. I would open up socket and seal any holes, gaps and cracks and refit, that will stop air whistling in through the face plate. Unfortunately not around behind the boards. Need to foam or seal the bottom as a minimum.

https://readinguk.org/draughtbusters/going-further/dot-and-dab/

Posted By: Davycrocketair coming through electric outlets and below kitchen cupboards

Electricians are the second worst offenders when it comes to creating drafts, close behind kitchen fitters.

I discovered this one today: the sparky has drilled a hole to run cables from the well-ventilated loft, down into the partition stud wall between two bedrooms, pic is from in the loft looking down at the hole. But not just a little hole!

Unsurprisingly, there was a gale blowing around inside the partition wall.

Davy, it might be that you have sparky damage like this, which if you find and plug, would reduce your draftiness?

There were also gales from under the kitchen units, as the fitters didn't feel that holes really count if they couldn't be seen behind the units. Particularly generous holes had been cut to feed the drain pipes through, and cables running up to splashback sockets. I foamed some by peering under with a phone camera. For some others I wound down the screw legs of the unit and slid it out forward from under the worktop to get at the holes.

Posted By: tonyYes, eps beads can help, they are both vapour open and air open but offer considerable resistance to air movement.

Can this be done diy or would a firm have to do it ?

Unfortunately not around behind the boards. Need to foam or seal the bottom as a minimum.

Ive done the top and bottom and in between as best i could but its non better unfortunately.

Posted By: WillInAberdeen

Posted By: Davycrocketair coming through electric outlets and below kitchen cupboards

Electricians are the second worst offenders when it comes to creating drafts, close behind kitchen fitters.

I discovered this one today: the sparky has drilled a hole to run cables from the well-ventilated loft, down into the partition stud wall between two bedrooms, pic is from in the loft looking down at the hole. But not just a little hole!

Unsurprisingly, there was a gale blowing around inside the partition wall.

Davy, it might be that you have sparky damage like this, which if you find and plug, would reduce your draftiness?

There were also gales from under the kitchen units, as the fitters didn't feel that holes really count if they couldn't be seen behind the units. Particularly generous holes had been cut to feed the drain pipes through, and cables running up to splashback sockets. I foamed some by peering under with a phone camera. For some others I wound down the screw legs of the unit and slid it out forward from under the worktop to get at the holes.

I imagine it has been a bit of this, theyre only interested in what the finished article.

Posted By: WillInAberdeen

Posted By: Davycrocketair coming through electric outlets and below kitchen cupboards

Electricians are the second worst offenders when it comes to creating drafts, close behind kitchen fitters.

I discovered this one today: the sparky has drilled a hole to run cables from the well-ventilated loft, down into the partition stud wall between two bedrooms, pic is from in the loft looking down at the hole. But not just a little hole!

Unsurprisingly, there was a gale blowing around inside the partition wall.

Davy, it might be that you have sparky damage like this, which if you find and plug, would reduce your draftiness?

There were also gales from under the kitchen units, as the fitters didn't feel that holes really count if they couldn't be seen behind the units. Particularly generous holes had been cut to feed the drain pipes through, and cables running up to splashback sockets. I foamed some by peering under with a phone camera. For some others I wound down the screw legs of the unit and slid it out forward from under the worktop to get at the holes.<

I foamed behind all the plaster boards from top to bottom before the kitchen was fitted, So im stumped as to why its no better.

Tony.

I'm not even convinced that the cavity insulation is joined to the l insulation to be honest.

How does fibreglass tie into celotex ?

As for the draughts I'll take another look at this perhaps I've missed something.

That's a lovely offer re the blower, whereabouts are you mate ?

<blockquote><cite>Posted By: tony</cite>Fibreglass need to fully touch foam sheet insulation, I like to tuck outside layer in behind sheet insulation.</blockquote>

I'll be surprised if that's the case. I'll investigate !

That will be great if you can let me know how much postage is I'll transfer you some money across mate.

Thank you.

Not good at photos on here as a moderator I can’t for some unknown reason post pics

https://www.dropbox.com/s/2u1di3id1du8hss/IMG_4898.HEIC?dl=0

The gun is connected to an old vacuum cleaner tube and to a compressor, you will need a compressor hose too , I use a 50l compressor and while injecting the compressor can’t keep up so runs all the time

Usually the motor and engine is the same on 25l and 50l compressors

Tony

For filling behind plasterboard I drill one 28mm hole near the top 200mm out from the corner, not into a dob of adhesive then roughly at 600cc.

Tell me your address, I will let you find an old vacuum cleaner hose and a delivery tube, 28mm copper or plastic or adapt something.

I will tell you postage cost afterwards likely £5 ish