Thermal regulations

National building regulations set minimum standards for the energy performance of buildings. These standards are routinely tightened to reduce the energy consumption of buildings and the associated carbon emissions.

UK — Approved Document L

In the UK, Approved Document L of the Building Regulations sets out the minimum standards for the conservation of fuel and power. For new dwellings, the maximum permissible U-value for windows is 1.6 W/m²K, with notional design values typically below 1.4 W/m²K. For non-domestic buildings, similar limits apply, and the overall building performance is assessed against a notional building target.

Window energy ratings

Windows in dwellings can be rated for their overall energy efficiency on a scale from A++ (most efficient) to E (least efficient), accounting for solar gain, thermal transmittance and air leakage.

Achieving compliance

Specify low-emissivity coated glass within the insulating glass unit.
Use argon gas fill in the cavity to reduce conductive losses.
Use warm-edge spacer bars to reduce thermal bridging at the perimeter.
Specify triple-glazing for very high performance applications.