PRINCIPLES/DESIGN AND CONSTRUCTION
Similarly, the designer needs to recognize the importance of individual envelope elements and their
impact on performance, and not compromise essential requirements for aesthetic or other
considerations. For example, flashing must extend beyond the face of the facade in order to
function properly, despite the fact that it might conflict with certain aesthetic goals. Similarly,
designers will sometimes limit the width of sealant joints without an analysis of the relevant
performance factors to determine if the width they select will be effective (O'Connor). The designer
must understand that these thermal envelope design considerations and requirements are critical
and must be incorporated into the envelope design.
As discussed in the section on air barriers, the importance of air leakage is not always appreciated
in the design and construction of buildings. As stated throughout these guidelines, the control of air
leakage through the use of an air barrier system is essential to good thermal envelope
performance. There is an unfortunate lack of appreciation on the part of designers, builders and
material suppliers as to the importance of air leakage (Handegord). It is sometimes assumed that
simply by specifying a vapor retarder or an air barrier, one has dealt with the problem. In reality,
achieving airtightness requires that an air barrier system is designed into the wall from the very
beginning. There is also sometimes a resignation that air leakage is inevitable and in fact desirable.
To the contrary, air leakage can and must be controlled to prevent a variety of performance
problems.
The AAMA manual on the Installation of Aluminum Curtain Walls is an excellent reference on
communication and coordination in the design and construction process. Although much of the
discussion is specific to aluminum curtain walls, the manual discusses general issues relating to the
responsibilities of architects, contractors and field personnel. The architect needs to be aware of
field procedures and conditions and develop clear drawings and specifications based on this
awareness. The architect should work closely with the contractor in developing the details to
facilitate fabrication and installation. Inspection during construction is identified as critical to
insuring that the specifications and shop drawings are closely followed. Architects should clearly
define maximum permitted tolerances in the alignment of the building frame, and provide for these
tolerances in the wall installation. The general contractor must develop the construction schedule in
consultation with the other players in the project, allowing sufficient time for other steps in the
process such as the development of the shop drawings, the fabrication of custom components, and
the assembly and testing of a mockup.
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