Elemental heat loss method: Using this method the U-value for each surface in the building must not exceed the values in the above table.

Overall Heat Loss Method: Using this method, the U-value for each surface must not exceed the values in the above table. A comparison between the volume of the building and the average heat loss through the different surfaces of the building determines whether it is suitable or not. The advantage of this method is that one surface can compensate for another.