PIR and Rockwool combined in garden room

[Montyman]

Hey everyone,

I am just about to build up the insulation layers in the walls and ceiling of a garden room that I am building. Moving from outside to in, I have cladding, then battens, then osb. Then within the studs I am considering using a 50mm layer of PIR, and then a 50mm layer of sound insulating Rockwool, before the usual layer of vapour control plastic sheeting and sound control plasterboard.

I am doing this as I need to balance both sound and thermal insulation - our house is near to a busy a road, and we want to use the room 365 days a year.

I plan to do the same thing in the ceiling, albeit with a 50mm ventilated void above the PIR before the bottom of the roof roofing OSB, to deal with the condensation – a cold roof design.

Does anybody have any experience of building up insulation in this way and can anyone see any problems with this approach as opposed to using 100% PIR or 100% Rockwool?

Thanks

Tom

 

[Deluks]

It could be problematic, moisture could pass through the rockwool, from the inside, and condense on the back of the PIR, flip it the other way round, rockwool facing outside, and use a breather membrane under the battens.