May 7, 2022

Glazing Thermal Performance Updated Building Regulations Approved Document L

Written by Rebecca Clayton

low carbon new build home with high performance glazing

Overview of the updated Building Regulations and changes to Approved Document L for Thermal Performance of Glazing  

The new version of Approved Document L came into effect on 15th June 2022. This Building Regulations update is part of a larger £6.6 billion update to the requirements of buildings in England with the aim to improve the energy efficiency of buildings.  

The updates will change the minimum thermal performance for glazing on new build houses and house extensions, bringing new building works in line with the government’s aims to achieve zero-carbon homes by 2025.  

These updates have been largely welcomed by the architectural community who have long been campaigning for higher performance requirements for new build houses.   

Simon Allford (former President of RIBA) described the changes as “bringing us one step closer to decarbonisation” but called for further tightening if we are to achieve true decarbonisation.  

This update to the performances of houses is a stepping stone to the much more stringent performance criteria that will come into effect in 2025 as part of the government's Future Homes Standard.  


Updates to Approved Document L Names 

updated building regulations thermal performance of glazing for new build dwelling approved document L

One of the main structural changes to Approved Document L is the amalgamation of the four existing documents into just two. The 2016 Approved Document L split the requirements for performance over four documents:  




    • Approved Document L2A – new building non-dwellings  


    • Approved Document L2B – work to existing non-dwellings  


Under the 2022 update these documents have been combined into two volumes:  


    • Approved Document L Volume 1 – work to any dwelling (new or existing)  


    • Approved Document L Volume 2 – work to any non-dwelling (new or existing)  

Updated Thermal Performance for Glazing on New Build Houses  

Architects designing new build dwellings will need to look at the building as a whole and calculate the target energy efficiency rates based on the Standard Assessment Procedure. This is very similar to the previous L1A calculations for TFEE and TER.  

They will then need to design a house that reaches these target rates with updated thermal performance for the glazing.  

building regulation L glazing for new build homes

If the architects are designing the house using the Notional Dwelling as detailed in SAP they have a listed series of U values that each element of their building has to adhere to.

Glazing on the Notional Dwelling has a maximum Uw value of 1.2 W/m2K. There are also limits on the g value, LT and orientation of the glazing (it has to be in the same plane as the building).  

Architects wishing to design a more bespoke house will use the Limiting Standards detailed in Section 4.

The maximum thermal performance of glass using this method is 1.4 W/m2K however, a higher performance will most likely be needed. This option provides a greater scope of design freedom to architects, allowing for more diverse designs that still adhere to the stringent performance requirements.  

Read More about the updates to Thermal Performance for Glazing on New Build Houses 


Airtightness for New Build Houses  

All new build houses will now have to complete an air pressure test on completion.  

Requirements for the minimum level of air tightness are listed within the performance tables of part L depending on whether the house is designed under the Notional guidance or limiting standards. Buildings as a whole will need to achieve between 5m3/(h.m2) and 8m3/(h.m2) and 50 Pa.  

This requirement will lead to changes in how glazing is installed and designed as part of the building envelope.  



Updated Thermal Performance for Glazing on Extensions and Renovations   

The maximum Uw value of glazing on an extension has also been improved.  

All glazing to extensions or renovations will now have to meet a maximum Uw value of 1.4 W/m2K. Rooflights must achieve 2.2 W/m2K and external glass fire rated door sets 1.8 W/m2K.  

building regulation L glazing for work to existing dwellings

Highly glazed extensions (extensions over 25% glazing) will now need to provide a calculation to show that the overall structure meets the performance criteria. This can be done via SAP or a weighted U value calculation.  

There are various listed exemptions for works to listed or historical buildings. The focus on these projects is to maintain the character and historical significance of the building with the requirements of Approved Document L should be achieved wherever reasonable.  

For a more in-depth overview of the requirements of glazing to extensions or renovations read our article.  


Crossover with Other Areas of Building Regulations  

This update to Building Regulations is part of a larger review of building performance.  

There have also been significant updates to Approved Document F (Ventilation) and the publishing of the new document O to combat overheating. Follow IQ on your chosen social media feed to get our upcoming articles about these changes.  


Transition and Key Dates 

The updated Approved Document L was published in January 2022 and will come into effect on 15th June 2022. Any project which has not received planning permission by this date will need to adhere to the updated version of Building Regulations.  

thermal performance of glazing for dwelling extension approved document L

Projects which have obtained planning permission before 15th June 2022 can adhere to the previous iteration of Approved Document L as long as they start on site prior to 15th June 2023.  

If you are unsure if the new Approved Document L requirements will affect your project, contact your local building control body.  

If you have any further questions about the thermal performance requirements for the glazing on your project, or how you can adhere to the latest standards, get in touch with the technical team at IQ.