The requirements around window installation in the UK have changed significantly, and for installers and fabricators the implications are substantial. Approved Document L (Conservation of Fuel and Power) places increasing emphasis on energy efficiency and limiting heat loss through the building envelope, making good junction design an important part of achieving overall building performance.
What has changed?
Approved Document L sets out energy performance requirements for buildings in England. Changes to the regulations have increased the focus on the performance of both new and replacement window installations, including the interaction between the window, the surrounding building fabric and the installation detail.
The industry has moved beyond considering the performance of the glazing alone. A good centre-pane U-value is only one part of the picture. Whole-window performance, junction detailing, airtightness and thermal bridging at the frame-to-wall connection can all influence the overall energy performance of the building.
What does verifiable energy performance actually mean?
Demonstrating building performance increasingly requires appropriate calculations and supporting technical information. Key considerations include:
U-value calculations — whole-window U-values consider the performance of the complete window rather than the glazing unit alone and form an important part of assessing heat loss through the building envelope.
Ψ (psi) value calculations — linear thermal transmittance at construction junctions can be assessed and accounted for within energy calculations. At window openings, thermal bridging at the frame-to-wall junction can have a direct impact on overall building performance.
Airtightness detailing — appropriate sealing of the window-to-wall junction helps maintain the continuity of the airtight layer and reduce uncontrolled air leakage around the opening.
The challenge for installers and fabricators
Every building is different. In retrofit projects particularly, wall constructions vary, reveal depths differ and existing construction is rarely consistent. Getting the calculations right and selecting appropriate products for each situation requires technical knowledge that extends beyond traditional window installation expertise.
That can present a genuine challenge for businesses that have historically focused on fabrication and fitting rather than energy performance calculations and building physics.
How Lynvale can help
At Lynvale, we work directly with window installers and fabricators to help address the technical requirements surrounding window installation and building performance. We supply expanding foam tapes, airtightness membranes and thermal break solutions, alongside technical support to help ensure products and details are appropriate for the project.
Our team can assist with:
- U-value calculations for specific window installations
- Ψ (psi) value calculations at window junctions
- Airtightness detailing advice and product specification
- Guidance on window installation requirements for new-build and retrofit projects
If you’re an installer or fabricator looking for straightforward technical support with window installation, airtightness and thermal performance, get in touch with the Lynvale team.
