Rooflights and Part L Building Regulation Changes (June 2022)


The Part L Building Regulation are among the most important regulations to help maintain a conducive environment for people. Although there have been many significant changes and innovations in the building and design industries arising from climate change, globalisation, and many other factors. These regulations can remain stagnant and out of date Thus, the Part L Building Regulations provide minimum criteria for architects, designers, and contractors. The recent changes in the Part L Building Regulations were a huge step forward in the government’s goal of making all new homes in England carbon neutral by 2025. These new laws establish efficient use of energy and power in new buildings.

Read on to learn more about how rooflights contribute to the new requirements of Part L Building Regulations.

What Are The Latest Changes To Part L Building Regulations?


The new changes to Part L Building Regulations state that all new homes must create 31% fewer carbon emissions than what is now permissible under the existing Part L laws [1]. As a result, new homes must meet the higher energy performance criteria established by the new laws during construction. And for a home to be energy efficient, it must comply with the new rules. Besides that, it contributes to a better building’s structural integrity.

However, there are many advantages to this new regulation. The government’s focus on energy efficiency is critical in economic and environmental realms. The government urges homeowners to explore energy-efficient solutions since they reduce CO2 emissions while increasing the structure’s overall condition. Building a new house or modifying one requires familiarity with the applicable rules. Thus, this also applies to rooflight U-values.

What are U-Values, and What is Required for Rooflights to Meet Part L Building Regulation?

During installation, the thermal transmittance of rooflights, skylights, and roof windows is essential. And this is expressed as a U-value measure in Watts per metre square Kelvin (W/m2K). When the U-value of a building is low, it indicates that the structure efficiently reduces heat movement.

According to the new building regulations [2], the minimal allowable U-values

for rooflights is 2.2 W/(m2K) for rooflights. And for this, the Building Regulations require Rooflights with three layers of polycarbonate or a double glazed unit because of the high insulation values.

However, to accurately determine if an element matches the new limiting U-value figure, the U-value of the component must be computed in the proper plane – either horizontal or vertical – of the component. The fact that the identical product may be tested in either a horizontal or vertical position makes a substantial variation to the final U-value number, making a significant impact. A lower (better) U-value is obtained in the vertical than horizontal.

According to the new regulations, a vertical position for roof windows should be considered when calculating U-values. However, when calculating U-values for rooflights, it is essential to consider their horizontal location. Although further tips from the Building Research Establishment’s BR 443 [3] show U-values for roof windows and rooflights are often given in the vertical plane when installed. However, it is possible to compare several items employed at various angles with this method. Thus, to calculate heat losses from buildings, U-values should be calculated to the plane of the component as it is mounted in the structure.

Thermal Bridging and How It Affects the Part L Building Regulations

Thermal bridging is a term used to describe a hole in the insulation. Thermal bridging is a source of heat loss and condensation in a closed environment. Heat loss in a building substantially influences its energy efficiency, making it difficult to reduce carbon emissions.

However, cold bridges, also known as thermal bridging, ensured that new builds and rebuilt houses comply with the new Part L Building Regulations on U-value for rooflight.

The good news is that there are ways to address thermal bridging both before and after its effects.

Correct design: Thermal bridging will be considered while selecting materials and assembling windows, doors, roofs, and envelopes during installation. The possibility of thermal bridging will almost certainly be considered in new construction, but such may not apply to older homes.

Energy Audits: It is possible to feel the coolness but not know where it is coming from without an energy audit. So, consider the possibility of doing an energy audit to identify and locate the cause of thermal bridges.

Adding Insulation: Heat loss through thermal bridges is possible; thus, insulating your surroundings can help you save money on energy bills.

Correct Installation: Try as much as possible to avoid thermal bridges from the beginning by having rooflights and windows fitted by professionals who understand thermal bridging and how to prevent it.


In terms of increasing the appearance and feel of a space, a rooflight can make a significant difference. That’s why you should work with solutions designed to manage rooflight thermal bridging and ensure that professionals install them. So if you want to begin installing rooflights in your house, get in touch with us at ADD LITE Rooflight access. We are UK based manufacturer of rooflights and roof access products. We’ll provide you with an accurate quote right away, so you won’t worry about any hidden fees or shocks. Call us at 01922 714091


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