Posted by: lcowie | November 16, 2010

R-Values and U-Values

Have you ever heard of R-13 insulation? R-Values are one of the easiest concepts to grasp in a BPI training course. There’s a real nifty trick I can teach you about calculating R-Values and U-Values.

First, R-Value stands for the resistance to heat transfer through a wall or a door. Heat will come in contact with a home, and the R-Value attached to a material indicates how much the material will resist the heat. The bigger the R-Value, the better.

Wood allows more heat transfer than insulation. The general rule of thumb is that less wood is good. You want as little wood as possible on the outside of the house. It is less efficient at blocking air flow. Even staggered 2 x 4s have insulation paired with them.

The U-Value is the transmittance of heat through a window. Once again, the U-Value will indicate how much heat has passed through the window. If the U-Value is low, this means less heat has been transmitted.

The nifty trick for calculating R-Values and U-Values is called the “1 over” rule. Basically the R-Value and U-Value are inverses of each other. You can convert between R and U by using 1/R or 1/U. You’ll need to do this easy conversion when adding up wall resistance or determining U-Value weighted area averaging. Both are easy concepts, but somewhat difficult to explain.

I might try to explain U-Value weighted area averaging another time, so stay tuned!


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