Article #1466 - REScheck Webcast Questions - Windows

This article is based on questions asked during both the May 6, 2005 REScheck Training Webcast and the July 28, 2005 REScheck Training Rebroadcast as well as questions received through email following these events. The original language of the questions and answers has been modified to make them as generic as possible while retaining the applicable specific information.

What if windows aren't chosen at time of REScheck forms being completed? Can we state a SHGC and show on front sheet under notes as being the maximum when actually chosen?

Solar heat gain coefficient (SHGC) The SHGC is the fraction of incident solar radiation admitted through a window.

The code requires the U-factor of any glazing be from the NFRC label of the manufactured product or the default tables for maximum U-factors and SHGC must be used. The SHGC default values in the code do not meet the .40 SHGC mandatory requirement for locations with < 3500 heating degree days. Therefore, locations in areas needing to meet the mandatory .40 SHGC will need to either choose windows that will meet code prior to completing compliance or get approval from the code official if using values that are not from the default table or manufacturer label.

The following link offers additional information on this subject:

How Do I Demonstrate Compliance with the SHGC Requirements in the IECC?

The Importance of Vapor Retarders

Does the software account for air infiltration values for windows?

No, the software does not account for air infiltration values for windows.

Do I have to enter each window individually or one lump area amount?

If all the windows have the same U-factor and assembly characteristics, the user can enter the total area of all windows as one item. Keep in mind, if more than one wall is entered in the program, any windows and doors that are part of the individual walls should be entered under their respective walls.

For windows, do I specify casement, picture, or double hung?

No, you only need to enter the assembly type, calculate the rough opening area of your glazing, and input the U-factor from the manufacturer label.

What is a thermal break in a metal frame window?

The most common solution to the heat conduction problem of aluminum frames is to provide a thermal break by splitting the frame components into interior and exterior pieces and using a less conductive material to join them. Current technology with standard thermal breaks has decreased aluminum frame U-factors (heat loss rate) from roughly 2.0 to about 1.0 Btu/hr-sq. ft-°F.