"Fenestration Beyond Standards
Successfully integrating windows, storefronts, and curtain walls
by David W. Altenhofen, CSI, CCS, AIA
Reprinted with permission of The Construction Specifications Institute
99 Canal Center Plaza, Suite 300, Alexandria, VA 22314, from The Construction Specifier

Specifications

Similar to detailing, standards are only the starting point for successful window and curtain wall specifications. As discussed above, unedited manufacturer standard specifications will confound a detail Likewise, standardized master specification systems, such as American Institute of Architects (AIA) Masterspecâ„¢ and the Construction Sciences Research Foundation (CSRF's) Inc.'s Spectext®, are only starting points for project-specific specifications. Minimum performance values suggested in off-the-shelf master specs are frequently inadequate for project conditions beyond low-rise residential or light commercial work. The criteria developed during selection of the system must be carefully incorporated into the specifications to ensure the completed building performs as desired.

It is especially important to cover minor details that could seriously affect performance. Requirements should include manufacturer tests be based on windows substantially similar to project conditions. Two excellent examples of this are multiple units, ganged together, or units installed with perimeter trim or receiver channels. AAMA 450, Voluntary Performance Rating Method for Mulled Fenestration Assemblies, is the standard method determining the performance of mulled assemblies. However, details many manufacturers provide for mulling units together or for adding trim have never been performance tested. (It is of little use to specify a pressure-equalized rainscreen window rated to an architectural window performance class of 60 (AW60) and set it into untested, barrier-type perimeter receiver channels with a mullion joint of a single line of sealant.)

The specifications must also include requirements for quality control and testing during the construction period. Although there are standards for many individual laboratory and field tests, there are no standards explaining how and when to apply them. The architect must rely on his own knowledge or retain a qualified consultant to determine testing protocol. Opinions vary widely on testing order, modifying standardized procedures, and determining passes and fails. Lab testing can easily require half a dozen different tests, performed in specific order, with air and water penetration tests repeated periodically for a total of a dozen or more individual tests.

Finally, the specifications for all of the materials and systems adjacent to the windows, storefront, and curtain wall must be coordinated. For example, a vapor retarder generally should seal to the window frame to maintain a continuous envelope. By coordinating provisions between the window, insulation, vapor retarder, and sealant specifications, the seal cannot be missed.