Garden building - separate VCL or just foil-backed PIR?

[oliwoodings]

Hi folks,

 

I'm in the process of building a 6x5m timber-framed low-occupancy garden building, which will be used as a massage studio by my wife. I'm current at the stage of insulating the walls, and the makeup so far looks like this:

• Tyvek Housewrap
• 9mm OSB
• Timber frame, with 100mm foil-backed PIR
• <Separate VCL, or just tape the foil?>
• 47mm service battens
• Plasterboard

 

My question is about whether I really need a separate VCL, or whether i would be fine relying on the foil-backed PIR, as long as I make sure everything is taped up really well (including the studs)? And if I really do need a separate VCL, should i go for a proper product like Tyvek Airguard Reflective, or will polythene be fine? I'm seeing really mixed opinions everywhere

 

Thanks in advance for any input anyone has!

 

Oli

[jayc89]

In theory, taping over the PIR joints should be fine. I've done both, just out of paranoia, it also allows for a better join at junctions, IMO. 

[oliwoodings]

7 hours ago, jayc89 said:

In theory, taping over the PIR joints should be fine. I've done both, just out of paranoia, it also allows for a better join at junctions, IMO. 

Thanks, that's helpful! I should be good with taping then for the walls and floor.

 

I'll need a separate vcl for the roof since theres a 70mm void for services so taping, would there be any practical difference between a basic polythene and something more advanced like a foil-based reflective one?