Weatherization and home performance practitioners should reconsider the value of window treatments, especially storm windows. Early energy conservation programs overused storm windows and storms were subsequently banned from some weatherization programs because weatherization agencies selected storms through personal preference. Storms are thought of as a measure that will be overused because they are easy to install and the installers stay clean. Today storm windows may suffer some unfair prejudice in energy-program policy.
Study of Window Treatments
I read a 2011 report today on extreme cold-weather qualitative testing for window treatments by the Cold Climate Research Center (CCRC) in Fairbanks Alaska. The experimenters compared the performance of shutters, blinds, storm windows, and curtains installed on double-pane insulated glass windows (which, experimenters assume, has inadequate thermal resistance for the Alaska climate).
The experimenters rated the window treatments for the following characteristics:
• Condensation Resistance
• Insulation Value
• Ease of Installation
Results of Study
Interior curtains, blinds, and shutters failed the qualitative testing because they increased window condensation compared to double-pane insulated glass. Condensation increased because these interior window treatments reduce the temperature of the window glass without stopping moist indoor air from moving in next to the glass and depositing condensation and ice on the window. No surprise here.
Exterior rolling shutters and sliding foam shutters got fairly high marks from the CCRC for condensation resistance and insulation value. However the affordability and ease of installation prevent the widespread use of these exterior window treatments.
The best performers, in my reading of the CCRC report, are the interior and exterior storm windows. Both interior and exterior storm windows reduced condensation compared to the double-pane insulated glass by itself. Affordability, insulation value, durability, and ease of installation for the storm windows were all rated good.
Tips for your Storm Windows
Here are some ways I’ve used to make storm windows cost-effective and valuable to the occupants.
- Decide which primary windows need to open for egress and ventilation and which don’t. Seal the primary windows that aren’t required for egress or ventilation and install a fixed interior or exterior storm window, which is less expensive than an opening storm window.
- Any fixed-glass section of a primary window is a good candidate for a fixed interior or exterior storm window panel.
- Use low-e glass in storm windows unless dust and dirt are major problems in between the primary and storm windows. Install the low-e surface toward the window’s interior rather than facing the indoors or outdoors to keep it clean for as long as possible.
- Specify exterior storm windows when the durability of the primary windows needs protected.
- Specify interior storm windows that are airtight enough to provide good condensation resistance.
- Use a sun-blocking low-e glass on windows that are a solar heating problem in summer.
- In cold climates, consider using an inexpensive low-e primary window installed inside the existing primary window for superior energy performance. This is sometimes called a double window.