Air barrier systems speaks to what are air barrier systems, why use air barrier systems and air barrier types are used to limit air leakage into and out of a building. Its conditioned space must be completely surrounded by barrier materials, creating an uninterrupted barrier system of surfaces, membranes, manufactured components, gap fillers and joint sealers that can effectively resist air pressure differentials across this boundary.
Careful attention to detail during design and construction is required to achieve this goal. All potential discontinuities in the barrier systems such as gaps between panels, laps in sheet materials, transitions between dissimilar substrates, fastener penetrations for structure or services, installation space around window and door frames, junctions between foundation, wall and roof assemblies, gaps between operable doors and windows and their frames must be made airtight.
They may be made airtight by the use of tapes, sealants, caulks, flashing, gaskets and other materials that can themselves meet the air permeance limits and structural requirements of an barrier material.
Due to the significant air pressure differentials acting across the barrier system, even small gaps can allow large volumes of air and water vapour to pass through the building enclosure and must therefore be minimized to the greatest extent.
Air permeance standards for the performance of assembled barrier materials are less stringent than those for individual materials, reflecting the reality that flawless, continuous sealing between materials and components is never possible.
Recommendations for the maximum air permeance of air barrier assemblies, that is, collections of materials responsible for the air barrier performance of a complete wall, roof or floor system are in the range of 0.01 to 0.05 cfm/sf @ 1.57 psf (0.05 to 0.20 L/sq meter @ 75 Pa).
Acceptable air leakage rates for whole building barrier systems, reflecting the combined performance of a building’s connected air barrier assemblies, fenestration and other enclosing elements can be expected to be even greater.