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Uo of Standard 2x6 Wall Assembly R-23 in cavities; framing = 23% of wall area Without windows: R-18 Overall With windows at 15% of wall area: Window U = 0.30, R = 11 Overall

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...

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