Article #110 - How Do I Show Energy Code Compliance for Site-Constructed Glazing Systems in Commercial Buildings?

Example of site-built glazing (church).

Compliance for site-built glazing systems is comparable with other assemblies within the building envelope, but it can be challenging because documentation on glazing performance values [U-factor, Solar Heat Gain Coefficient (SHGC), etc.] is not usually available. Without documentation, default values from the code may be used, but these values assume the worst thermal performance and often present code compliance challenges. Default values can be taken from tables in Chapter 1 of the IECC, Appendix A of ASHRAE 90.1-1999 or 2001, or by right-clicking on the appropriate cell in the COMcheck-EZ software.

The National Fenestration Rating Council also has a rating program for site-built windows. If the site-built glazing used in your project has been rated through this program, the performance ratings can be used for energy code compliance.

Determining the overhang projection factor (PF).

Code compliance challenges can be alleviated somewhat if glazing overhangs that provide significant shading are used. Overhangs must be a permanent part of the building, however, before the credits can be applied. The projection factor (PF) will determine how much credit will be given.

The PF is calculated by measuring the distance from the edge of the overhang to the window (A) and dividing that distance by the distance from the bottom of the window to the lowest point of the overhang (B). The COMcheck software provides a convenient way to calculate projection factor and other envelope trade-offs.