Wednesday, February 20, 2008

Making Windows More Energy-efficient, Part 1

Restoring Old Windows for Energy Efficiency

Green building is not only about new construction. Reusing and improving an existing structure rates very high on the green scale, and right now many people are looking for ways to “green” their existing home. Of course, there are many ways to do this, on many different levels, and deciding exactly where to start can be a very daunting task. Well, never fear because there is a lot of information out there from many reliable sources (check out Dovetail and also the list of other blogs on the right) and now many green building programs have their own remodeling standards that can be used as guidelines for your green remodeling project.

Of course, you don’t have to completely remodel a home to make it more green than before. Here is a short list of ideas to improve a home’s greenness right now, without renovations. One thing that is common to all green remodeling lists is improving energy efficiency, and many times that involves fully replacing the windows on the home. This method can be very effective, but also very expensive. Thankfully, the alternative method of repairing existing windows can also improve a home’s energy-efficiency cost-effectively while maintaining the architectural design integrity of the home. Read on for some tips on restoring old windows for energy-efficiency.

Thinking Beyond Glass

Even with the best glass available, glass as a material is still inefficient. Windows are typically measured in U-value, which is inversely related to R-value, and while they do not measure exactly the same thing, it is helpful when comparing them to walls, which are measured in R-value. To give you an idea, 6” fiberglass batt insulation in an exterior wall is typically labeled R-19. A window that is double-paned low-e argon-filled has a relative R-value of around 3. One pane of glass without low-e glazing is around an R-1. Older homes typically have single-pane glass and a storm window, which results in an R-2 (if properly sealed). You can get new windows with triple-pane argon-filled low-e glazing, but you would be lucky to achieve over an R-4.

So when thinking about windows, look beyond just the glass. Contrary to popular belief, it is not the fancy glass in new windows that makes them better, but the tightly-sealed components of the window. Older windows may become warped (due to a variety of elements), causing the seals loosen, allowing air to flow and heat to transfer. A window in this situation will not be efficient, even if it has low-e argon-filled glass or better. A properly-sealed window makes a big difference.

Types of windows

The type of material your window frame is made from will determine how much heat is lost as well. There are many types of windows.

This article focuses on wood windows because they are the most common in older homes. Wood windows have great insulating properties, use natural materials, and have the ability to be repaired. They are also susceptible to rot, but can last a long time if leaks are sealed and the wood is treated properly or even clad in vinyl or metal. Wood windows typically are nailed together and not glued, and can be disassembled and reassembled in pieces, giving the option of being repaired rather than completely replaced. There are many books on wood window repair. Repairing the cracks and holes in the wood not only makes it look better but also can plug potential air leaks as well.

Properly sealing the home and windows is the best way to ensure that moisture does not collect and cause wood to decay. The next entry will focus on how to seal leaks in old windows to maximize energy-efficiency.