WHAT ARE WE TESTING FOR?
The National Building Code of Canada (NBCC), Part 5, Section 5.4, Subsection 5.4.1.2., stipulates four key requirements for successful air barrier systems: airtightness, continuity, structural integrity and durability.
Air tightness – Subsection 5.4.1.2. Sentence 1 states that “. . . sheet and panel type materials intended to provide the principal resistance to air leakage shall have an air leakage characteristic not greater than 0.02 L/(s·m2) measured at an air pressure difference of 75 Pa.” While there are many commercial air barrier materials that satisfy this requirement, these materials must be joined into a system so that the system is airtight under different indoor environmental conditions. Recommended maximum leakage rates for air barrier systems in exterior envelopes are provided in Appendix A of the NBCC.
Continuity – Subsection 5.4.1.2. Sentence 7 states that “The air barrier system shall be continuous (a) across construction, control and expansion joints, (b) across junctions between different building assemblies, and (c) around penetrations through the building assembly.” That is to say that not only is it important that no gaps exist in the individual components that comprise the system, but the components must be joined such that there are no gaps in the system as a whole. It is air leakage at the connections between air barrier components, and at penetrations through it, that usually determine the overall effectiveness of the system.
Structural Integrity - Subsection 5.4.1.2. Sentences 8 and 9 state that “An air barrier system installed in an assembly subject to wind load, and other elements of the separator that will be subject to wind load, shall transfer that load to the structure.” Specifically, it shall be “. . . designed and constructed to resist 100% of the specified wind load as determined in subsection 4.1.8.” The air barrier system must be able to resist peak wind loads, stack pressure effects or sustained pressurization loads without exhibiting signs of detachment, rupturing or creep load failure.
Durability - Subsections 5.1.4.1 and 5.1.4.2. detail the requirements for resistance to environmental loads and resistance to deterioration. The air barrier system must be durable, meaning it must be able to perform its intended function, be compatible with adjoining materials and resistant to the mechanisms of deterioration that can be reasonably expected given the nature, function and exposure of the materials, over the life of the building envelope.
These four requirements represent the minimum performance requirements of an air barrier system. In some instances, for certain buildings, the specifications on the particular project will demand that the performance standards of the system exceed those contained in the NBCC. Note also that the air barrier system must not only meet the requirements of the national code, but any provincial/state or municipal codes as well. Reviewed by Guiseppe Strazzeri.