Foil Taping PIR Boards... Or Not?

[benben5555]

Hi, I'm building timber frame. Got 140mm mineral wool between the studs and then 50mm PIR over, then air tightness membrane over that. Have people taped the joints on the PIR with aluminium foil tape? Or is this not necessary given the air tight membrane will be going over the top anyway?

 

Thanks 

[Marvin]

1 hour ago, benben5555 said:

Hi, I'm building timber frame. Got 140mm mineral wool between the studs and then 50mm PIR over, then air tightness membrane over that. Have people taped the joints on the PIR with aluminium foil tape? Or is this not necessary given the air tight membrane will be going over the top anyway?

 

Thanks 

I always usually do studwork filled, Vapour barrier PIR sealed and then fire resistant plasterboard, because then item cut into the walls (electrics for instance avoid cutting the membrane....  Others may disagree.

[Redbeard]

If it is something like Intello, which is an intelligent VCL *and* an a/t layer, yes, don't tape, but a/t is not necessarily vapour-tight, so if it's a run-of-the-mill a/t layer you arguably need a VCL too. (which may be the taped jts, but I would use air- (and vapour-) tight tape, not foil tape. 1. For improved adhesion and 2. particularly at corners, foil tape can tear, and then it is not a VCL anymore.

[Roger440]

17 minutes ago, Marvin said:

I always usually do studwork filled, Vapour barrier PIR sealed and then fire resistant plasterboard, because then item cut into the walls (electrics for instance avoid cutting the membrane....  Others may disagree.

 

Tha manufacturers disagree. Vapour barrier on the warm side is the consistent guidance as far as i can tell. 

 

You are increasing the risk of interstatial condensation.

[Roger440]

15 minutes ago, Redbeard said:

If it is something like Intello, which is an intelligent VCL *and* an a/t layer, yes, don't tape, but a/t is not necessarily vapour-tight, so if it's a run-of-the-mill a/t layer you arguably need a VCL too. (which may be the taped jts, but I would use air- (and vapour-) tight tape, not foil tape. 1. For improved adhesion and 2. particularly at corners, foil tape can tear, and then it is not a VCL anymore.

 

Its SO hard to get clear advice on this.

 

Ive just done my workshop "warm" room.

 

PIR foil taped, then vapour barrier over. Overkill? Maybe. But better safe than sorry. Rework will be painful, both of time and expense.

[jayc89]

I always fill and tape PIR regardless. Belts and braces. 

[saveasteading]

12 hours ago, Roger440 said:

PIR foil taped, then vapour barrier over

That must be optimum. The gap between boards is sealed and becomes an air cell.

Any tape would do though. Shiny surfaces are only effective when  facing a void.