PRINCIPLES/DESIGN AND CONSTRUCTION
Air Barrier Systems
Because of the importance of including air barriers in building envelopes, and their common
omission in most buildings, this section gives special attention to how air barrier systems fit into the
design and construction process. Many architects and designers are either unfamiliar with air
barrier systems or do not consider them to be significant relative to the many other issues with
which they must deal. This lack of familiarity exists because most discussions of air barriers exist in
the technical literature, not in the publications to which designers are more often exposed. Also, the
promotion of most new ideas within the construction industry is largely product or sales driven.
Since an air barrier is a system as opposed to a single material, it is not promoted in new product
columns or by writers of architectural publications.
Designers are often unfamiliar with the importance of air barrier systems and how to incorporate
them into building envelope design. Before the design process even begins, it is relevant to
determine whether anyone on the design team is aware of or experienced with air barriers and able
to incorporate such a system into the envelope details and specifications. If not, it probably will not
happen. If such a person is part of the team, he or she still may not have sufficient influence to
pursue the issue. Once the design development phase has begun, the commitment to a
continuous, well-supported and buildable air barrier should already be in place. This commitment is
likely to be challenged with statements such as: "We have not done this before...We have a vapor
retarder, what do we need this for?...lt is not in the budget." The case for an air barrier must be
made strongly and clearly; its function and requirements must be explained. When a commitment
has been made to an air barrier system, its compatibility with the basic envelope design, the
structural system, and the thermal insulation and vapor retarder systems must be reconciled early
in the design process. An air barrier that is incorporated as an afterthought can not be effectively
integrated with these other systems and will not perform adequately. The compatibility of the air
barrier system and the major details, e.g., wall-floor, wall-window, corners, columns and parapets,
should be examined early in the process.
As the working drawings are being produced it is important that the air barrier is correctly and
consistently applied to all primary and derivative details. This is particularly important for masonry
walls where the working drawings are used for construction without the benefit of separate
construction drawings. All members of the design team must understand the principles of the air
barrier so that all details are developed consistently, and all details must be reviewed with respect
to the air barrier. As the specifications are developed, it is essential that they contain a requirement
for an air barrier. The requirements should specify that the air barrier be identified on shop
drawings and should address the structural adequacy of the air barrier system.
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