Windows: From the Weak Link in the Building Envelope to the Linchpin

When the main concern is energy efficiency, focusing on the cost-effective improvement
to a home’s windows is the ultimate investment

By Manny Hondroulis

Windows are an architectural necessity for any home or office, as people require daylight for multiple reasons. We want to know and see what is outside, whether the view is of the Rocky Mountains or of a crowded street in New York City. Daylight has multiple health benefits too, including increased productivity and mental stimulation. But the windows that afford us sunlight also come with drawbacks. They are typically the most inefficient part of the building envelope, allowing in the sun’s heat inside during the summer and allowing the escape of manmade heat to the outside in the winter. According to the Department of Energy’s website, the average household spends almost half of its annual energy budget on heating and cooling. (The other half is devoted to hot water heating and maintaining internal loads.)

Despite advancements in window coating technologies, the U.S. lags far behind Europe with respect to glass efficiency. Putting aside different test methods and standards to account for nominal discrepancies in evaluations, it seems that European law and consumers demand more from their glass and window manufacturers than we do in the U.S. An easily relatable example is that triple pane glass is more prevalent in Europe than it is here. I suspect that at some point regulations will require us to catch up, but what happens to all of the existing glazing already in place?

Adding an additional pane of glass can have tremendous benefit in reducing summer heat gain and winter heat loss. The Solar Heat Gain Coefficient (SHGC) and U Value of standard 1” (¼” glass, ½” air gap, ¼” glass) insulated glass decreases significantly from those of ¼” single pane glass. Replacing single pane units with double pane or double pane units with triple pane is not in the budget of every builder. And relatively inexpensive power rates (when compared on the international market) provide a payback of 20+ years. If replacement is not financially feasible yet a home is too cold in the winter, too hot in the summer, or both, there is something to be done.

Window film is a retrofit product designed to increase the energy efficiency of existing or budget-friendly windows and is a fraction of the cost of window replacement. It is made of a thin (approximately .002”), clear polyester containing an insulating coating that adheres to existing glazing. When installed properly by a professional, it is barely noticeable.

In existence for over 50 years, it is one of the home improvement industry’s best kept secrets. Those who are familiar with window film may have seen it installed on cars and recognize it as dark, purple, and bubbled. Automotive films, while related, tend to be less sophisticated than the products used for office and home. Today’s architectural window films are made to be clear and bubble-free.

3M Company, makers of Post-it® Notes and Scotch® Tape, holds the original window film patent dating back to 1966. The Minnesota manufacturer recently introduced its new Thinsulate™ Climate Control Window Film which is almost the equivalent of adding an extra pane of glass at a fraction of the cost of window replacement and without changing the appearance of the window. The 3M-owned brand name, Thinsulate, is appropriate for this innovative new film as the term suggests insulation from extreme weather. Just think Thinsulate gloves, scarves, hats, and boots. Its effect on existing windows is significant; especially when you consider that it is approximately the same thickness as a Post-it Note and not an extra piece of glass separated by a ½” air gap.
Just how much more cost effective is window film installation compared to window replacement? Labor and material to install Thinsulate Climate Control Window Film by a 3M certified professional is typically $15-$20 per square foot of glass area, which on an average residential window (30” X 56”) is $175-$233. Compare that to the price of window replacement: Home Advisor estimates $300-$700. That is up to a 200 percent difference.

Like new windows, Thinsulate window film is warrantied by its manufacturer. 3M Company provides a lifetime guarantee that protects the original purchasing homeowner from bubbling, cracking, crazing, peeling, blistering, delamination, and discoloration. 3M also protects against thermal shock fracture and seal failure for up to 60 months and 40 months, respectively.
Windows are a necessity, yet are inefficient by their very nature. We continue to pay an economic and social cost to pump out hot and cold air to create a comfortable living environment. When you consider the cost of heating and cooling, a cost-effective home improvement like Thinsulate Window Film to existing glazing is a worthwhile investment.

Manny Hondroulis is a Vice President for Energy Products Distribution, a master distributor of 3M Window Film products, and works with end-users to make an informed decision about whether or not window film is an appropriate solution for a given building envelope. He may be reached at