White Paper: Windows And Walls, A Double Standard In Energy Efficiency

By Bruce Lang, Southwall Technologies

The big secret regarding energy efficiency in retail facilities is window glass, which compared to insulated walls and ceilings, is a terrible energy loser. While we expect that energy-conserving walls and ceilings will dramatically insulate against heat loss and block direct solar radiation, knowledgeable store managers 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 and contractors. These knowledgeable observers rightfully see such defacto energy-conserving windows as a substantial improvement over conventional insulating glass with insulation performance of R-2.