Understanding vapour barrier, help!

[GlynJ]

Hi, this is my first time posting on here I'm just looking for bit of advice on insulation and the vapour barrier?

My garage is single brick and I had a local builder batten out the garage ready for the insulation. What I noticed is that he fitted a plastic sheet behind the batons before fixing them. He then recommended I use Kingsspan a normal plasterboard afterward.

My confusion is with the plastic sheeting install behind the batons (wall side), would this cause a problem and stop vapour from escaping?

 

[noseall]

The plastic sheeting is more likely a moisture barrier with regards to external ingress.

Your vapour barrier (VCL) should go directly behind the plasterboards and (if possible) in front of the insulation.