ASHP & triple glazing

[AE-NMidlands]

I planned to screw the pir board (foiled both sides) to the existing battens under the original plasterboard which I didn't intend to remove. I'd then glue fix the standard paperbacked 9.5mm pb to the foil of the pir board

I hadn't thought of foiled PIR. That has the vapour barrier and the ally tape completes the seal on the room side. If it is rigid enough to take screws (or you can find wide-head screws that will pull themselves in flush) then all's good, if not then maybe a few screws right through your final pb layer, recessed just enough to only need a surface touch up?

[Joeboy]

Would it not be easier just to stick prefinished plasterboard already stuck to foil insulation direct to the wall?

No timber required, quicker easier install,

That's clever, make up my own Sandwich boards on the horizontal. Could weigh them down with plate weights then fire them on as one pre prepped package once dry. That really is clever.

The temp difference within the room. 17.1 to 17.3 on the bad wall and 18.9 on good internal walls. I'll.keep looking for prebuilt all in ones. The £8 per can for adhesive kills the price run though. I'd rather pva the plasterboard to the pir foil backed board then screw through both to known fix points with same glue on back of pir foilboard as back up. This is just me playing in my mind. I'll happily pay full whack but the fun isn't in just doing that.







Me n swmbo use this spray contact adhesive in our furniture side of things. It really is excellent. I wonder?

https://www.poundwholesale.co.uk/151-he ... 00ml?gQT=1

I'm pretty sure we could make up a 1 ft sqr test piece and see how it goes?

[Andy]

I screwed a few screws into the pir with the big plastic spacers. They meant the pb didn’t sit terribly flat with the pir. Then I used the normal 20cm spacing in the plasterboard. I had some very long screws because they had to get through 63 mm before the wood. Don’t get the double thread screws as they really struggled and some even snapped from the torque. None of the boards slipped once the screws were in. However lots of screws is lots of cold bridging. So screwing in the pir and then dot and dabbing the pb might be better. I’m not sure how the foil will hold up over time though.

[Joeboy]

I screwed a few screws into the pir with the big plastic spacers. They meant the pb didn’t sit terribly flat with the pir. Then I used the normal 20cm spacing in the plasterboard. I had some very long screws because they had to get through 63 mm before the wood. Don’t get the double thread screws as they really struggled and some even snapped from the torque. None of the boards slipped once the screws were in. However lots of screws is lots of cold bridging. So screwing in the pir and then dot and dabbing the pb might be better. I’m not sure how the foil will hold up over time though.

Good to know Andy. I'd only be going through 30mm total new board (42 total before wood). Dare I say it, comes down to the torque I suppose to clamp the sandwich in place while countersinking into the pb.

[NoraBatty]

Ours are screwed in at 400mm spacings so i presume into battens, with what looks like nylon wall plus and metal screws.
These need tightening a bit as there is movement as said above thats blown the plaster off.
I will be adding a 25mm board behind these anyway so will swap for nylon screws if i can. The rest of the upstairs is 62mm ipb, the gable wall is only 37mm ipb and the difference was about 2 degrees surface temp when -2 outside.


They used the SIPP insulation method here, and sipps product brochure suggests nylon screws to be used or sheathed to cut down on thermal bridging. You can certainly see the fixing points easily enough.

[Joeboy]

Just goes to show how impactful the fixings can be. A plan begins to form, we'll see how well i can bond bare pb to a foiled pir. It's worth at least trying on a small scale to have the knowing. Probably do two with one being lightly sanded foil to increase the adhesives bite. See if I can spot the difference.

Great photos BTW.

[NoraBatty]

Just goes to show how impactful the fixings can be. A plan begins to form, we'll see how well i can bond bare pb to a foiled pir. It's worth at least trying on a small scale to have the knowing. Probably do two with one being lightly sanded foil to increase the adhesives bite. See if I can spot the difference.

Great photos BTW.

I would be tempted to use these for the Pir, then stick the pb on the pir with foam. Its not the weight necessarily, its the shearing force from the bonded pb sticking out a further 25mm from the wall. 25kg ish per 8*4 pb sheet, is alot to ask. Imo.
https://www.insulationsuperstore.co.uk/ ... f-100.html

These are what I want to use, for batten fixing
https://www.insulationsuperstore.co.uk/ ... f-100.html

[Andy]

pted to use these for the Pir, then stick the pb on the pir with foam. Its not the weight necessarily, its the shearing force from the bonded pb sticking out a further 25mm from the wall. 25kg ish per 8*4 pb sheet, is alot to ask. Imo.

It was the shearing I was worried about. But a butt ton of screws seemed to be fine. Not a smidge of movement. We are quite a few years in from completion and there are no cracks in the full plaster skim.

What are the nylon screws you all mention? I can't seem to find anything that isn't for attaching stuff to the wall.

[Andy]

If you go metal screws, this is the type of fine thread to avoid https://www.screwfix.com/p/easydrive-ph ... pack/16374
This is the one that worked. https://www.screwfix.com/p/easydrive-ph ... pack/54411

I used the original timber and it was just too tough for the fine thread to go in.

[NoraBatty]

What are the nylon screws you all mention? I can't seem to find anything that isn't for attaching stuff to the wall.

Sorry Andy, thats what i meant, screw the lot to the wall using a nylon screw or at least a screw sheathed in nylon to reduce bridging. Hence the links i added
The plaster has popped off of most of our screws now on the gable wall and held elsewhere, but there is a bit of play in the wall when you push, so these just need retightened then covered again if we were to leave them ans not add more insulation.
I would prefer larger washers holding it all together though as you can see there is nothing but a wall plug and the screw currently.
But you do get a colder spot visible on thermal that way.
No condensation etc visible with naked eye, so no actual cold bridges, but it is visible with a thermal camera so will be having an effect.

Joe wants to foam it to the wall, so i suggest he screws the pir to the wall with nylon, then foam the pb onto the pir which should reduce the cold spots.