insulated pb on a window reveal how to join the corner?

[zachmbutcher]

Hi all, in short how do you finish the corner of the window reveal/wall when using Insulated PB?

I am adding insulated plasterboard on the inside of the bedroom. Its a cavity wall. using 37.5mm on the wall and 25mm for the reveals. I'm struggling to find any videos or answers on how the board should meet in the corners and I'm struggling to explain it too, so hopefully this makes some sense.

A butt joint would clearly be the easiest, but i don't think i can leave the PIR layer exposed for plastering, though I'd be using tap/angle bead on the formed corner. From a couple of sites i have managed to find something i have read i should remove a strip of the PIR, the thickness of the side reveal board so that the two PIR layers meet and the plasterboard meets PB to PB.

i have tried to attach a pic of an example with some scrap board of the butt joint or a partially removed PIR layer allowing PB to PB (two pics)

would you...
A) butt joint the boards then tape/angle bead the corner and plaster.
B) Cut back the PIR so that the PIR aligns behind and PB to PB aligns, then tape/angle bead.
C) something else (please let me know)

 

[Wayners]

Cut the foam off the back so you have 100mm plus 12.5..
Then slide right.

If that makes sense

You also have to cut 12.5mm off foam on the right hand side in photo on other bit to allow for plasterboard thickness

 

[zachmbutcher]

Cut the foam off the back so you have 100mm plus 12.5..
Then slide right.

If that makes sense

You also have to cut 12.5mm off foam on the right hand side in photo on other bit to allow for plasterboard thickness

Cheers wayners. Is that different to what I have suggested in option B ? I have removed some of the pir to slow the board to slide behind and ensure the plasterboard meets on the corner

 

[Wayners]

I guess so. Option B.
If you stuck the insulation on first like some do.
Then use standard sheets of plasterboard and stick on the insulation it works out the same.
You just need to then insulated board to fit