I made a start on our IWI; PIR adhered to the wall, VCL (not necessarily needed, but belts and braces...), battens mechanically fixed through and PB over the battens. In the rooms I've done so far, I've been putting a glob on acrylic sealant in the batten screw holes before driving the screw into the brickwork. On the ones I checked, there was a decent seal between the back of the batten and the PIR/VCL. But it's slow going.

 

For the next room(s) I'm considering running strips of butyl tape behind the battens with the expectation/hope that it will provide the airtight seal around the screw as it's driven into the brickwork. 

 

Pros/cons to either? Is one more foolproof than the other? Any other suggestions?

Given I already have the sealant, I'm going to continue using that. Allows me to use hammerfixings for areas where I want to hang heavy stuff too.