PRINCIPLES/DEFECTS
Air Leakage Defects
.
Discontinuity of air barriers
.
Inappropriate use of insulation or insulation adhesives as air barriers
.
Punctured or displaced air barriers
.
Polyethylene: inadequate support, lack of continuity
.
Inappropriate selection of sealant materials
.
Sealant failure due to differential movement
.
Lack of interior finishing
Achieving an airtight building envelope depends on the maintenance of a continuous air barrier
system over the entire envelope including the selection of appropriate materials and means of
attachment (Ashton, Handegord, Perreault 1986, Quirouette 1989). Air leakage defects include
designs that fail to maintain the continuity of the air barrier system, the inappropriate use of
insulation or insulation adhesives as air barriers, and the puncture or displacement of air barrier
materials either during construction or as a result of the movement of building components. While
polyethylene is a relatively airtight material, it will not perform as an effective air barrier when it is
not adequately supported or when used in situations where it is difficult to maintain continuity.
Additional sources of failure in air barrier systems include the inappropriate choice of sealant
materials given the conditions (e.g., temperature, humidity, solar exposure) to which they will be
exposed and joint designs and sealant selections that can not accommodate differential movements
within the envelope system.
Some cases of air leakage occur because air barrier and sealant joint details are not developed for
all locations in the envelope. While adequate details are generally developed for the more
straightforward connections, the more complex intersections of envelope elements are sometimes
neglected. For example, the details for the connection at the window head, jamb and sill may be
adequate, but no air barrier details are developed for the corners. Similarly sealant joints may be
designed for both horizontal and vertical panel joints, but no details are developed for sealing the
intersections between the horizontal and vertical joints. In these cases, achieving an airtight seal is
left to the installer or mechanic, who must develop a solution rather than employ a seal that has
been designed for the circumstances.
One important source of discontinuities in air barrier systems is a failure to finish the entire interior
facade of a wall system when this facade is serving as an air barrier. These failures sometimes
occur because only the visible portions of the interior facade are finished, allowing air leakage
though the unfinished areas.
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