Approved Document L: How Approved Document L1B impacts windows and doors

29 June 2021

Approved Document L is a set of British Standards used for the regulation of thermal efficiency in windows and doors.

Approved Document L1B, or Thermal Efficiency requirements for Windows and Doors, specifies that there must be an airtight seal to keep out cold draughts and maintain warmth within the building, in order to increase the level of energy efficiency in homes.

Approved Document L1B specifies the U-Value requirements, which is a measure of how well a window or door reduces heat transfer, measured in watts per square metre-kelvin.

In this article, we will take a closer look at how Approved Document L1B impacts windows and doors exactly.

What are the requirements for windows and doors under Approved Document L1B?

The lower the U-Value, the more energy efficient the window or door is. Approved Document L1B sets the minimum energy efficiency requirements for windows and doors.

The minimum requirement is a U-Value of 1.6W/(m2⋅K), applicable to all new windows and doors, regardless of material.

The Window Energy Rating, also known as the WER, is calculated based on various factors, this includes the U-Value, and provides a more overall idea of a windows overall energy performance. This is important as the WER is now also accepted as a way of complying with Part L1B of the building regulations when the window achieves a “C” rating or better.

With that being said, despite being used as part of the WER calculation, the U-Value can be different from one specification to another on the same product. However,  as this is not the only criteria that is used it means that a window can have the same WER as another even if the U-Value is different

Choose windows and doors from TruFrame

As you can see, in order to comply with the current building regulations, it is important that you choose windows and doors that are manufactured to the highest standards and from a trusted supplier. 

At TruFrame, we understand the importance of using quality products for installers which offer a low environmental impact with the ability to offer high levels of energy efficiency, which is testament to the continued investment and innovation in our fabrication facility. 

Find your nearest window or door supplier online, or contact us to open a trade account.