When building your house, one of the most important matters to consider is how to minimize heat loss from the building fabric as efficiently as possible and in the most economical way.

The term ‘Building Fabric’ encompasses the outer shell of the building and is made up of the External floor, walls, roof, windows and doors.

A U-Value is the measure of the rate at which heat is lost through the Building Fabric, so the lower the U-Value the better.

Thermal bridging and Ventilation aside, the best way to reduce heat loss in the Building fabric is to use Insulation. The use of Insulation will reduce the U-Value of the External floor, walls and roof elements. So, therefore the better insulated your home is, the lower the U-Value, the lower the heat loss through the building fabric, and the lower the cost to heat your house will be.

A U-Value is calculated using the thicknesses and Thermal Conductivities of the materials used for each element of the works i.e External floors, walls and roofs. The lower the thermal conductivity and the thicker the material the better (lower) the U-Value will be.

The Insulation used should be of a type and thickness to meet the requirements of the current Building Regulations. Please see below Table 1 from TGD Part L 2011 outlining the maximum U-Values permitted for each element when building a house.


There are many Insulation Manufacturers in today’s market.  Insulation is available in various forms, from rigid boards, to bonded beads to fibreglass.  Each form has individual Thermal Conductivities, thicknesses and all vary in cost.


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