"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

Standard performance specs, test methods, sizes, profiles, details... it might be reasonable to assume window and curtain wall systems can easily be selected, detailed, and specified through standards. On the contrary, specialized skill and knowledge are required to integrate windows into a building, and fenestration design certainly should not be limited by standards. Installing windows is rarely standard, as most designs require some degree of customization for anchorage, flashing, trim, perimeter seals, and continuity with the thermal envelope. Windows and curtain walls have a substantial impact on HVAC and electrical systems, and should be customized to suit the project. Furthering the need for customization, many of design issues are interrelated and sometimes mutually exclusive. The application of standards is simply inadequate.

Performance standards

Windows vary considerably in performance, from barely adequate under normal conditions to extremely tight during hurricanes. Most manufacturers test their products with the standardized method American National Standards Institute/American Architectural Manufacturers Association/National Wood Window and Door Association (ANSI/AAMA/NWWDA) 101/IS 2-97, Voluntary Specifications for Aluminum, Vinyl (PVC) and Wood Windows and Glass Doors. Performance values vary from air penetration of 2.06 m3/h at a test pressure of 75 P (0.37 cfm at 1.57 psf) to 0.56 m3/h at 299 P (0.10 cfm at 6.24 psf).

Water penetration values also span a similar range. This standardized measurement allows a relatively simply comparison between different windows. Acceptable performance for a window in a particular project cannot, however, be completely predicted by simply complying with one of the performance classes in ANSI/AAMA/NWWDA 101/IS 2-97. Of particular concern is manufacturer-advertised performance might be based on a window much smaller than the one required for the project, and may not be representative of actual project performance. Other variables-such as glass type, anchorage, and stiffness of the wall in which the window is mounted-can also result in a difference in performance between tested samples versus and the installed window.

Storefronts and curtain walls do not have a single performance standard, but rather a series of standardized test methods for establishing performance. The three primary weather performance standards are ASTM International E 283, Test Method for Determining Rate of Air Leakage Through Exterior Windows, Curtain Walls and Doors Under Specified Pressure Differences Across the Specimen; ASTM E 331, Test for Water Penetration of Exterior Windows, Curtain Walls and Doors by Uniform Static Air Pressure Difference; and AAMA 501.1, Standard Test Method for Exterior Windows, Curtain Walls and Doors for Water Penetration Using Dynamic Pressure.

Structural performance is measured by ASTM E 330, Test for Structural Performance of Exterior Windows, Curtain Walls and Doors by Uniform Static Air Pressure Difference. Thermal performance, U-values, and condensation resistance factors (CRFs) are measured under AAMA 1503-98, Voluntary Test Method for Thermal Transmittance and Condensation Resistance of Windows, Doors and Glazed Wall Sections, and standardized through AAMA 1504-97; Voluntary Specification for Thermal Performance of Windows, Doors and Glazed Wall Sections.