Windows and Walls A Double Standard in Energy Efficiency

The big secret regarding energy efficiency in co-ops and condos is window glass, which compared to insulated walls and ceilings, can be a source of serious energy waste. While we expect that energy-conserving walls and ceilings will dramatically insulate against heat loss and block direct solar radiation, knowledgeable condo boards and owners anticipate far less in the way of energy conservation from even the most energy-efficient windows.

The numbers speak for themselves. Walls with an insulation performance value of R-19 are considered to be the norm (R means resistance to heat flow the higher the number the better the insulation performance). On the other hand, windows with low emissivity (“low-e”) coated glass and inert gas fill that meet the coveted Energy Star® designation, and whose insulation performance tops out at R-4, are celebrated by architects, contractors and building managers. These knowledgeable observers rightfully see such de facto energy-conserving windows as a substantial improvement over conventional insulating glass with insulation performance of R-2.

But why do we expect our condos to contain R-19 insulated walls, while at the same time, be willing to accept R-4 windows? Such an energy conservation double standard exists because it is easier to be a wall than a window. Walls only have to insulate well. Windows must do a lot more.

Windows (specifically window glass) must be transparent and colorless, transmit natural daylight, reflect unwanted solar energy, decrease ultraviolet radiation that causes fading of condo components and furnishings, reduce sound transmission, and of course, insulate against heat loss. In addition, many windows must also open to provide ventilation and egress in emergency situations. Compared to walls, a window must simultaneously perform numerous functions, many of which are highly sophisticated.

Reducing Heat Loss

If the year were 1960 instead of 2010 perhaps we could maintain one energy conservation standard for walls and ceilings and another less demanding standard for windows and glass. But we can no longer afford to do so. Despite heavily insulated walls and ceilings and the popularity of Energy Star designated windows, 25 percent to 35 percent of the energy used in homes and buildings is wasted due to inefficient glass. So, it should come as no surprise that glass is responsible for more than 10 percent of the total carbon emissions in the U.S. annually and is a major contributor to global warming. In addition, inefficient windows and glass cause unhappy and uncomfortable co-op or condo occupants, who are often too cold in winter, too hot in summer, and paying more than they should in heating and cooling costs year-round.


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