Part L of the Building Regulations for England and Wales (Conservation of fuel and power) and Section Six (energy) of the Scottish Standards set the levels of thermal insulation required when carrying out building work, either for new build or refurbishment projects. These are expressed as a U-value which needs to be achieved. The required U-value will depend on the location of the project (England, Scotland or Wales), type of building (domestic or non-domestic) and the application (floor, wall or roof).
The tables below show the suggested U-values in England, Wales and Scotland. Note the distinction between the domestic and non-domestic columns. Below that, there are more detailed guides to the thermal insulation parts of Building Regulations / Standards.