Article #1499 - COMcheck Web-Based Training Questions - Curtain Walls

This article contains questions asked during the August 18, 2005 live broadcast of the COMcheck Web-Based Training session. The original language of the questions and answers has been modified to make them as generic as possible while retaining the applicable specific information.

Is a curtain wall a window or exterior wall?

Curtain wall assemblies cannot be entered in COMcheck as an exterior wall assembly because you cannot account for the solar heat gains from the glazing. Furthermore, curtain walls cannot be entered solely as a window due to the fact the program needs to associate windows to walls to calculate the window-to-wall ratio (WWR). These assemblies should be entered in the following manner:

• Choose "Other" as the assembly type from the drop down menu under Exterior Walls.
• Enter the total square footage for the entire assembly (including the framing)
• Enter the U-factor from the manufacturer for the framing or entire assembly
• Choose "Other" as the assembly type from the drop down menu under Windows
• Enter the estimated square footage of the glazing (this number will be slightly less than total square footage of the entire assembly). Basically you are subtracting the small amount of framing from the square footage (typically this will be a 1/100 ratio).
• Enter the U-factor from the manufacturer for the center of glass or entire assembly.

How would you calculate spandrel glazing in a curtain wall glazing system: as a window or a solid wall construction with a calculated U-value?

Curtain walls with spandrels should be entered as "Other" walls with their applicable U-factor of spandrel entered separately from the glazing portion. Calculate the entire spandrel area, framing, insulation, air films, etc., and enter in COMcheck as an "other" wall type. You can edit the word "other" and input the name of the wall system and then the overall U-factor of the entire wall.

What is the best way to distinguish between vision glass panels and insulated spandrel panels in an entirely glass high-rise?

Insulated spandrel panels can be entered as "Other" walls with the factory-tested assembly U-factors. Vision glass panels need to be entered as windows with their entire assembly U-factor, not just the center of glass U-factor.

Can you count mullion caps as part of the solid portion of a glazed wall system? Is the glazed portion counted in the window drop down literally the exposed glazing to the exterior?

No, if the assembly U-factor for the glazing includes the mullions. Otherwise, the mullion cap U-factor needs to be entered as an "Other" opaque wall. The glazed portion can be entered as "Other" window in the window drop down.

Can you count structural silicone in a butt-glazed system as part of the solid portion of the wall? Further, can you count the mullion behind the glazing in a butt-glazed system as part of the solid portion of the wall?

No. Structural silicone cannot be entered as a solid portion of wall if it is integral to the glazing.

How should you handle an exterior wall that is all storefront framing with various types of glazing with different U-factors?

Each window with a different U-factor should be entered separately as part of a single "Other" wall with an overall area-averaged U-factor. Some high window-to-wall ratio construction may be difficult to get to comply using COMcheck. In those cases, an energy analysis program may be used to show compliance using the performance approach.