Masonry - Thermal properties
The requirements for the conservation of fuel and power are given in the Building Regulations Approved Documents L1 (dwellings) and L2 (buildings other than dwellings).
Concrete masonry is an integral part of the calculations to show compliance and the thermal properties can have a bearing on the overall wall/floor/roof construction. For a given thickness, Aircrete blocks will tend to give better thermal insulation properties than aggregate blocks unless the later have insulation directly applied to them. In most cases secondary insulation will be required in the construction in order to meet the elemental U values (0.35 W/m2K for external walls and 0.25 W/m2K for ground and exposed floors) for England and Wales but some flexibility is allowed if the target U-value or Carbon Index Methods are chosen for dwellings. Buildings other than dwellings have different routes to show compliance.
For further information see the Concrete Block Association or the Autoclaved Aerated Concrete Products Association