Foil backed plasterboard onto insulation panels.

[24PoW]

I have eaves in my bedroom and adjoining bathroom that I have removed the old lathe and plaster from (1920s property). Before I sheet them up and plaster I'm planning on fitting 50mm insulating panels into the rafters (100mm deep, so leaving 50mm for air flow/ventilation). Advice i've also had is to use foil back plasterboard seeing as that will be against the rafters.
Is it ok to use foil plasterboard as well as the foil covered insulating panels - or will taping up the boards and rafters suffice, then hang the normal gyproc onto this?

 

[RandomGrinch]

Only a DIY'er, but I would use aluminium foil tape to cover the joints between boards and over the rafters (and any dents/tares in the foil backing). That would create a continuous VCL and you wouldn't need foil backed plasterboard.

Ideally, and if you have space, you would also want a layer of insulated plasterboard (or similar), beneath the rafters to help avoid cold bridging.

...and although you have a 50mm ventilation gap, again ideally, you should have decent ventilation in the soffits, or over fascia and in the ridge, to allow cross ventilation, over the top of your new insulation.

 

[noseall]

I have eaves in my bedroom and adjoining bathroom that I have removed the old lathe and plaster from (1920s property). Before I sheet them up and plaster I'm planning on fitting 50mm insulating panels into the rafters (100mm deep, so leaving 50mm for air flow/ventilation). Advice i've also had is to use foil back plasterboard seeing as that will be against the rafters.
Is it ok to use foil plasterboard as well as the foil covered insulating panels - or will taping up the boards and rafters suffice, then hang the normal gyproc onto this?

Nothing wron with belt and braces approach. We foil tape all layers of (foil sandwich) insulation and use duplex boards.

Vaulty2

• noseall
• 15 May 2022

Foil3

• noseall
• 2 Apr 2019

Bow3

• noseall
• 24 Apr 2016

..and foam any larger gaps prior to foil taping.