Triple glazing in apartments to comply with new Part L

The Government’s preferred fabric energy efficiency standards for Part L 2021 will require costly enhancements, such as triple glazing in apartments, for compliance.

The Government has set out two options for future Fabric Energy Efficiency (FEE) targets. Their preferred option is a significant enhancement over current requirements. This is still in consultation, but it is assumed that this is what will be adopted within the update to Part L 2021 in June next year. This makes it more challenging to achieve FEE targets.

Our initial calculations show that meeting this new FEE target in apartments would be extremely challenging without including triple glazing. However, if triple glazing is included, other specification elements can largely stay the same (such as wall insulation thicknesses and air permeability targets).

To help meet Part L targets, the amount of glazing in a dwelling should aim to be less than 25% of the floor area of each apartment. The reduced glazing area can also help to reduced overheating risk, which will be assessed under Approved Document [X], which is anticipated to be enforced in line with the updated Part L from June 2022.

In houses, improved fabric energy efficiency measures will also be required, but it is likely that double glazing could still be applied without unrealistic improvements needed elsewhere.

Other specification elements that will need further consideration under Part L 2021 include:

• Further passive measures to mitigate overheating risk to comply with Approved Document [X].
• More bespoke psi value calculations required for junctions, as accredited details will no longer be available to use. Thermal breaks will need to be considered as early as the planning stage.