Mastering compliance: How suppliers can help with Parts L & F


To create a ‘stepping-stone’ towards the mandatory Future Homes Standard in 2025, changes to Part L & F of the Building Regs came into effect in 2022. Colin Wells of Keylite Roof Windows discusses how window manufacturers can help housebuilders produce the required uplift in energy efficiency.

With several changes made to the Building Regulations in England and Wales last year, including additions to ‘Conservation of Fuel and Power: Approved Document L’ and ‘Ventilation: Approved Document F’, housebuilders have been looking for products that take the headache out of compliance by ensuring they meet current requirements.

The purpose of Part L is to ensure energy efficiency in buildings, with new and existing homes in England now being subject to higher building performance targets in an interim step towards the Future Homes Standard – which is due to arrive in 2025.

When it comes to heat loss, one of the biggest issues for housebuilders is thermal bridging, meaning an area of a building construction which has a significantly higher heat transfer (loss) than the surrounding materials. One example of where this would occur is with junctions around windows, including roof windows.

If this area is not insulated it can lead to cold bridging on roof windows; this is where the gap between the roof and window is left exposed to the temperature differentiation between the outside and inside, which can eventually lead to condensation and mould.

Some manufacturers have designed features that reduce the possibility of this occurring, ensuring products are designed in such a way that housebuilders don’t have to consider the ‘gap.’ These features help eliminate thermal bridging, which reduces the risk of non-compliance, and delivers a build that is closer to the expected energy performance.

However, while a product may say it meets Part L or has a certain U-value, this may not be the case once it is installed. Therefore, it is vital that housebuilders specify products that help mitigate the gap between performance on paper, and actual performance of a finished build. 

A patented Integrated Expanding Thermal Collar has been developed to ensure the thermal integrity of the window and roof is as designed, thus removing the reliance on an additional collar and helping achieve Part L requirements. It also improves airtightness and psi-values for SAP, further helping housebuilders. 

In another move towards the Future Homes Standard, last year’s update to Approved Document F relates to improving ventilation in homes. With a drive towards more energy efficiency, homes are now designed to be insulated and as airtight as possible to reduce draughts and avoid heat loss. The result of this is an increase in the retention of moisture in the home with a lack of air circulation and a need to maintain healthy air quality.

To balance any lack of natural ventilation, mechanical ventilation and/or background ventilation are made requirements for new homes under the updated Building Regulations. Now, when housebuilders specify new windows in their new developments, trickle vents must be installed, or sufficient background ventilation must be provided by other means.

Once again, Part F requirements for background ventilation are supported thanks to innovations such as a window top handle which allows for controlled trickle ventilation when the window is fully closed and securely locked. The National House Building Council (NHBC) will not accept other window types that provide background ventilation by being latched in the partially opened position.

This year also saw an update to ‘Overheating: Approved Document O’, specifically paragraphs 3.8 to 3.10 ‘Protection of Falling,’ which states that openings which are intended to be open for long periods to reduce overheating risk might pose a higher risk of falls from height. 

Again, some window manufacturers have taken the initiative, design product features that help support housebuilders who urgently need to find answers to meet this latest update to Building Regulations. 

Colin Wells is head of technical at Keylite Roof Windows