2.4 Building Envelope, Air Barrier and Fire Stopping

Mechanical insulation interacts with building components such as walls, partitions and roofs, and these boundaries need to be considered in design and installation of the mechanical insulation system.

An air barrier is required by the building code to maintain a controlled interior environment. Air barriers are different than vapour barriers in that an air barrier is to stop air infiltration or exfiltration, whereas vapour barriers slow down or arrest moisture movement by vapour diffusion through building enclosure materials. At any location in the building’s enclosure, an air barrier seal is subjected to a range of air pressure differences in both directions. The highest design loads are usually due to wind pressure during storms; these are high enough to cause many sheet materials to vibrate and tear off their fastenings. An air barrier must withstand much higher physical forces than a vapour barrier.

There are occasions where piping, conduit or ducting penetrates the contained building envelope. Those components are usually insulated and wrapped or covered, up to the point of a penetration. At that juncture, the component must be air sealed in conjunction with the building’s air barrier seal. The objective is to eliminate air leakage in either direction. Further fire stopping may be required to meet to the Building Code requirements for the ratings of the wall assemblies. Fire stopping materials may function as air barrier materials; however this should be verified with the manufacturer. All firestopping materials proposed to be used must conform to ULC-S115 and CAN/ULC- S101. The suitability of the material should be confirmed with the Authority Having Jurisdiction by the contractor prior to its application.