Garden room walls

[metasoma]

Hi,

I'm in the process of building a garden room/office. The walls are comprised of 4"X2" studs with 11mm OSB wrapped in breathable membrane. I'm just about to start insulating the interior using 75mm PIR. I was then going to wrap it internally with vapour control layer before boarding.

Anyway, chatting to a builder, he says to use insulated plasterboard then you won't need the vapour barrier. Is this correct, and if so which insulated plasterboard would be ideal?

Thanks

 

[mrrusty]

As you've built the wall with studs, the insulation goes between the studs, then a VCL then PB. There is no point using insulated PB either between the studs or on top of them! (unless you want thick walls!) You were right first time. Next time maybe use SIPs - they save a heck of a lot of work and are very similar in price. https://www.simplysips.co.uk/pricing/

 

[metasoma]

Thanks. You've confirmed everything I had planned!

 

[catlad]

If you don't put insulated plasterboard on the inside wall you will have cold bridging with the stud walls.

 

[metasoma]

If you don't put insulated plasterboard on the inside wall you will have cold bridging with the stud walls.

Because I'm only using 75mm PIR?

 

[mrrusty]

If you don't put insulated plasterboard on the inside wall you will have cold bridging with the stud walls.

It's true the u value of the timber will be less than the insulated sections, but the area of the studs is small so the heat loss through the studs is minimal; whether you think it is worth spending the extra for even more insulation and slightly reduced internal space is your call. IMHO for a garden room with cladding over air gap over membrane then OSB and insulated stud wall it's going to be plenty warm enough as you have built it.