Guillermo writes from somewhere in Chile: “I know that the “U” value is reciprocal to “R” Value. I know the “R” value, but how do I calculate the “U” Value?
The answer to your question can be easy or complicated, depending on whom you ask and the level of detail and accuracy you need or want. For example, here is a formula I found online: U = 1/ {(1/ho) + (l/ k) + (1/hi)}. A simpler answer is to add up the R-values of materials, airfilms and air spaces from one side of the assembly to the other, then invert this number to obtain the U-value. U-value indicates the thermal conductivity of a system, such as a wall assembly, while R-value indicates the thermal resistance of an individual material or component of the wall system. R-value is the measure most commonly seen on insulation products. The higher the R-value the better the insulating performance will be. A well-insulated wall will typically incorporate R 13 to R 21 insulation. Well-insulated attics and cathedral ceilings may have R 30 to R 49. You can find more information online at various Websites, including CLEAR (Comfortable Low Energy Architecture), a website hosted in the U.K. to
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