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Changes to Part L of the Building Regulation

Window systems and the new Part L – what the industry needs to know

The Government ­­­has announced changes to Part L of the Building Regulations which will come into force from June 15th, 2022. These are designed to reduce the carbon emissions of our buildings and will have significant implications for the design and construction of buildings – including window and façade systems. 

What do the changes mean?

By 2025 the Future Homes Standard will demand new buildings produce at least 75% less carbon emissions when compared to current levels. To ease the way the Government has introduced new Part L regulations as an interim measure, in which all new buildings will need to generate 31% fewer CO2 emissions than the current regulations allow. This interim measure comes into force on June 15th June 2022.

The new legislation means the thermal regulations for windows and openings are changing. The current U-values for the thermal transmittance of windows and openings into all settings (new and existing buildings) are to be upgraded.

For specific details on changes to U-values please refer to:

Approved Document L, volume 1: dwellings (Table 4.1 page 24, and Table 4.2. page 25)

Approved Document L, volume 2: buildings other than dwellings (Table 4.1 page 25)

What you need to do

We’d urge specifiers, contractors, fabricators, and installers to start to prepare now - June 2022 will be with us before we know it. We recommend you familiarise yourself with the New Part L building regulation and ensure you understand implications for window systems as well as other parts of the building envelope. Also consult with specialists to understand how the change in U-value requirements will impact the aesthetics and cost of façade systems. This will enable you to begin planning future specifications and installations so can select the most suitable products, that are fully compliant and meet the clients design requirements.

Rigorous evaluation and testing

Over the last year we’ve rigorously benchmarked the new U-values against our current products and planned new products to ensure they comply. This involved a detailed FEA analysis using specific thermal modelling software to calculate the thermal performance As well as carrying out additional analysis associated with the BFRC (British Fenestration Rating Council) which is a labelling system for window and doors products, to give our customers the utmost confidence in their purchasing decision.

Reynaers has a comprehensive range of products - windows, doors, sliding doors, folding doors, and curtain walls – that fully comply with the new regulations.

Some of our products also exceed the new U-value requirement, providing additional thermal performance and making them future proof, in lieu of additional regulatory changes in the future.

Be reassured with Reynaers

We’ve been preparing for these changes for well over a year to ensure we can provide our customers with absolute reassurance that when they specify or install Reynaers products they are fully compliant with the updated regulations.

As a company, we’ve been closely involved in the development of the new regulations. John McComb, Technical Director, has been a member of the Council for Aluminium building for more than 20 years, and sits on various committees.

The company is also a member of the Curtain Walling and Cladding Technology (CWCT) group and is actively involved working in collaboration with trade bodies and the Government.


To help support the industry, in the coming months we’ll be announcing a series of in-person and online events as well as a range of guidance materials to make it as easy as possible for our customers to choose products that comply with the new Part L and meet the right performance and aesthetic standards.


More info