When it comes to improving the energy efficiency of a building, lots of attention is paid to insulation R-values, thermal bridges, and air sealing. But don’t forget the windows, which account for the biggest energy loss in a high-R wall.
When it comes to improving the energy efficiency of a building, lots of attention is paid to insulation R-values, thermal bridges, and air sealing. But don’t forget the windows, which account for the biggest energy loss in a high-R wall.

If you look at a building's thermal envelope as a six-sided cube, the walls represent the largest surface area and have the weakest R-value. So if the goal is to improve the thermal efficiency of that envelope, the walls have the most room for improvement. We can increase their R-value by making them thicker or by using insulation with a higher R-value per inch, but unfortunately, framing a thicker, better-insulated wall is only one piece of the puzzle. We also have to deal with the thermal bridging associated with traditional framing methods and we have to improve the windows. In fact, it's the windows that have become the weakest link in a high-performance wall.

Today's builders are learning to mitigate thermal bridging by using alternative framing techniques, continuous exterior rigid foam products, or both. The reason is obvious: Wood framing materials have a resistance to heat flow (R-value) that is roughly one quarter that of common insulation products such as fiberglass and cellulose. Because heat...

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