Heat loss occurs due to heat being transferred from the inside of a home through the building fabric and lost via drafts of warm air through gaps in walls, floors, roofs and lofts etc.

The U-value of a building’s fabric element, known as its thermal transmittance, is a measure of how effective the element is at insulating and reducing heat loss. The lower the U-value of a building’s fabric, the more slowly heat is transmitted, and the better it insulates.

Adding extra insulation to a building fabric element reduces the U-value and heat loss. However, if the installation is badly designed or fitted poorly, the heat loss will be greater. The installation must also be carefully designed to avoid condensation. This is known as a ‘fabric first’ approach and is key to creating and improving heat retention.