Insulated Plasterboard - Advice please

[rgregson1919]

Hello All
We hod our loft converted some years ago. They didn’t use insulated plaster board by the stairs which is an outside wall (9” solid and rendered).
We get these cold spots in condensation season where the dabs of plaster adhesive are creating bridges. Having done a bit of research, I think putting something on top might be a bit of a bodge.
I am considering taking all the plaster off, back to brick and then 35mm thermaline plus board held on with adhesive - followed by a skim.
35mm might cutting it fine as the min width by the side of the stairs is 25mm. I might have to go with 27mm board.
I don’t want to batten as I don’t want to loose any space in the stairwell.
Has anyone any better ideas before I go ahead with this?

Questions:
If I go back to brick, what it the best way of treating the brick wall before sticking on the boards?
Do I also need some mechanical fixing because of regs? If so what fixings?
What is the best adhesive to use for the board? I see Screwfix to something called Insta Stik
Many thanks for any advice/tips.

 

[cdbe]

Stick it on with plasterboard foam - doesn't allow passage of moisture.

 

[rgregson1919]

Hello, many thanks. Any particular brand of foam you recommend?

 

[cdbe]

Any, as long as it's specifically for plasterboard. Plenty available at Screwfix etc.

 

[rgregson1919]

many thanks sorry for delay in reply.