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Calculating thermal resistance and U value

The thermal conductivity of a material and its thermal resistance are related by the equation:

For example consider a 0.22 m thick brick wall with a thermal conductivity of 0.6 Wm-1oC- 1.
Thermal resistance = 0.22/0.6 = 0.367 m2oCW-1.

The U value of a barrier is defined as:

So for the brick wall the U value would be 1/0.367 = 2.72 Wm-2oC-1. If the wall had a lower thermal conductivity its thermal resistance would have been greater

© Keith Gibbs 2007