Air can leak out between the inner perforated acoustic liner and the outer sheet, exiting at each end of the roof where the bargeboards are to be fitted.
 

Membranes must be properly sealed on overlaps and eaves and verges.
 

Verge details need careful thought on how to seal them. This one has no sealant under the membrane thus allowing air underneath the membrane.
 

Obvious gaps where the block wall meets with the timber roof. Also there are gaps where the timber rafter goes through the block wall.
 

Air passes through the fibre glass insulation. To effect a good air test result use some other form of sealant such as spray foam or foam fillers.
 

Lack of site supervision and a design fault has led to this huge gap between the brick wall and the front face of the sheeting rail where the side sheets will be fitted.

The gap is up to 35mm wide and if the length and width of the building are taken in to account it all adds up to a total of 4.9m2 of gap!