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Thermal Bridging Calculation

user-509810 | Posted in Energy Efficiency and Durability on

I would like to compare various roof deck insulation solutions for an attic remodel. I would like to know the formula that I can use to calculate the whole wall R effect of thermal bridging on the insulation option chosen.

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  1. GBA Editor
    Martin Holladay | | #1

    There are simple back-of-the envelope methods, and more sophisticated methods.

    The best computer modeling program for thermal bridges is called THERM. If you want the best answer, hire an energy consultant to analyze your options using THERM.

    For a back-of-the envelope calculation, divide the roof into two areas. One area is the area between the rafters. You can calculate the R-value of this area (presumably based on the insulation installed between the rafters). Then calculate the area of framing (if expressed as a percentage of the total roof or wall area, this is called the "framing factor"). You can calculate the R-value of the framing separately. (The R-value of softwood lumber is about R-1.2 per inch.)

  2. user-509810 | | #2

    Thanks Martin

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