Garden room vapour barrier

[Canski]

Hi all,

Now that the house is 95% complete ( I’m just waiting for the electrics to the heat pump to get sorted to give us heating) I move on to the garden room. 
 

I built it prior to the main build and used it as a site office / store/ temporary toilet. It is stick built out of 4 x 2 with 90 mm celotex between the studs and the roof out of 7 x 2 with 90 mm of celotex between the rafters and a gap above for ventilation. I am now in the process of installing an extra 25 mm of PIR to the inside which I will seal and tape prior to adding 2 x 1 to create a set is void prior to boarding. The outside will be clad in either cedral cladding or timber. 
 

Seeing as the PIR will be well sealed and taped on the inside do I still  need to install a vapour barrier as well ? 

 

[Redbeard]

Strictly no, if you are 100% certain that your tape is good - 'proper' airtightness tape (often green, not foil tape, ideally (altho there is good and bad foil tape). Since you are using a non-breathable insulant I think there's little reason for an intelligent vcl, so bog-standard 90 vcl or (stronger) visqueen should do.