What is a U-value? U-values explained | MyFoam.ie

# What are U-values?

### What is a U-value?

A U-value is the measure of the rate of transfer of heat. This is not the same as an R-value which is the measure of how resistant a material is to the transfer of heat. A U-value is measured in W/m^2K – Watt/(Metre squared)(Kelvin).

A U-value is the reciprocal of the corresponding R-value. If the R-value is 2, the U-value will be 1/2 or 0.5. If the R-value is 5, the U-value will be 1/5 or 0.2.

The higher the R-value is the lower the U-value is. This confirms the relationship between R-values and U-values. If the material is more resistant to the transfer of heat (high R-value), it will transfer heat as a lower rate (low U-value).

There is no need to focus on both U-values and R-values as they go hand in hand. If you focus on increasing the R-value of insulation materials in your home you are guaranteed to have a decreased U-value.

### Why are U-values important?

Building regulations for Government grants require that U-values for houses must not exceed the following;

Roof   0.4 W m-2 K-1
Walls 1.1 W m-2 K-1
Floor  0.6 W m-2 K-1