Reminder – Insulating Rooflight Builder's Kerbs
A requirement in Part L 2021 (England).
What Do the Regulations Say?
Tables 4.1 and 4.2 relating to limiting U-values for fabric elements in new and existing buildings in both volumes of Part L 2021 include the following note relating to rooflights:
"An upstand built on site should not exceed a U-value of 0.35W/m²K"
This requirement applies to both new and existing kerbs.
Rooflight upstands supplied as part of the rooflight unit do not require additional insulation, as their thermal performance has already been included within the quoted rooflight U-value.
When Did This Come Into Force?
The requirement came into effect on 15th June 2022 for projects in England.
It does not apply to work subject to a Building Notice, Full Plans Application or Initial Notice submitted prior to that date, provided work on the building commenced before 15th June 2023.
Bauder Specifications and Drawings
All Bauder specifications and drawings now being produced reflect these requirements.
Rooflights supplied for installation onto builder's kerbs will be designed to accommodate the required insulation thicknesses.
Contractors should take these requirements into account when pricing and completing Bauder projects.
What Thickness of Bauder Insulation Is Required?
- BauderPIR FA-TE: 60mm
- BauderROCK: 105mm
- BauderGLAS T3+: 100mm
Rooflights supplied with an integral upstand do not require any additional insulation.
Builder's kerbs not supplied as part of the rooflight assembly should be insulated sufficiently to achieve a maximum U-value of 0.35W/m²K.
Can Insulation Be Incorporated Within the Kerb Instead of the Bauder System?
Unless an adequate AVCL is present on the inside face (warm side) of the kerb, there is a risk of condensation forming within the kerb construction.
This can lead to significant long-term issues. For this reason, Bauder does not recommend incorporating the insulation within the kerb itself.
If you have any questions, please do not hesitate to contact me.