GENERAL: Do joints between boards need to be sealed?

It is good practice to seal the joints between boards and building elements such as rafters and abutments, as this controls the rate of passage of water vapour through the structure and helps with air tightness. The two common methods are to use a self adhesive aluminium foil tape, or to use a conventional sheet vapour control layer, in either case abutments should be sealed with a low modulus silicon sealant