Achieving a low U-Value is an integral part of achieving the required levels of energy efficiency in an A-Rated house.

However not many people understand what is meant by a U-Value. One of the best definitions is provided by Sustainable Energy Ireland who state that “a U-Value is the measure of the rate of heat loss through a material.” Therefore in all aspects of design the self builder should aim for the lowest U-values possible. The lower the U-value, the less heat there is needlessly escaping through the roof, walls, windows and doors of the building.

The following is a practical illustration of the concept. While the Irish Building Regulations lay down certain minimum insulation U-value guidelines, A-rated houses must achieve lower levels while Passive rated houses must be lower still.