Tighter U-values on windows and doors
1st February 2022

Tighter U-values on windows and doors

Changes to Building Regulation Part L could impact on joiners making doors, windows, frames and architraves. David Hopkins, CEO of Timber Development UK, explains why.

The Department for Levelling Up, Housing and Communities has released new updates to Approved Document L of the Building Regulations in its continuing efforts to reduce UK greenhouse gas emissions and achieve a truly ‘net zero’ economy.

These changes are intended to be the next step for the construction industry as it moves towards the introduction of the Future Homes Standard, which is expected to demand that homes will be at least 75% more efficient than current Building Regulations dictate.

While the Future Homes Standard isn’t expected to be introduced until 2025, this interim update to Part L, which comes into effect on 15th June 2022, is implementing a 31% reduction in emissions for newbuild homes, compared to the current standards.

Any properties designed or renovated after this date must adhere to these stricter regulations, although any projects that have sought planning permission before June will have 12 months’ grace and can build to the previous standards until June 2023.

So, what does this mean for the woodworking and joinery trade? Well, as part of a rejuvenated ‘fabric first’ approach to building and construction, these Part L changes are seeking to reduce the amount of energy that is lost through the fabric of the building – and that means walls, doors, floors and windows are coming under particular scrutiny.

Following a consultation with industry carried out in 2019, the government has specified tighter U-values on windows, roof windows, rooflights and external doors in newbuild properties, and also on replacement windows, doors, new openings and extensions.

U-values are measured in W/m2K, and describe the amount of heat transferred through a square metre of a wall, door, floor or window, for example. It is hoped that tightening the U-values permitted in these areas of the external fabric of the building will help reduce the amount of heat and energy lost through ‘leakage; to the outside. It is important to note that these U-vales are minimum performance figures, and the construction industry is being asked to go further than these figures to improve efficiencies wherever possible.

The new minimum U-values vary depending on the type of door, window or rooflight, and Approved Document L gives guidance on how these figures can be calculated. For example, replacement timber windows being fitted into an existing dwelling must have a maximum U-value of 1.6W/m2K. It’s important to note that timber with different densities will have different levels of thermal conductivity, and this will have an impact on the overall U-value of the window frame or door that is constructed using that timber. Going forward this will require a review of the types of wood and wood products we use to manufacture these products particularly solid core doors.

You may find that your customers begin to ask for more information on how they can ensure the doors, windows, frames and architraves you create are as efficient as possible. Joiners and woodworking professionals who would like more information should contact their suppliers for more information, or visit for more support.


This article was first published in the February 2022 issue of Woodworking News.