Introducing the revised Approved Document Part L - Blog

Introducing the revised Approved Document Part L

Introducing the revised Approved Document Part L

Development George F. White 27th January 2022

The revised Approved Document Part L Volume 1 and 2, first published in December 2021, will be formally adopted on 15th June 2022 with a grace period until 15 June 2023 for previously approved planning permissions. Approved Document L Volume 1 deals with dwellings and includes a 30% decrease in carbon emissions along with an improved method of modelling for buildings. This document is designed to work in tandem with the recently issued Approved Document Part O.

The key difference is the way in which calculations are carried out. Using the previous Approved Document, carbon emissions from a poorly constructed building could be off-set using renewables such as PV panels in order to achieve a ‘pass’. However, the revised document includes an increase in the ‘backstop’ for walls, ceilings, etc.

For example, the  ‘backstop’ u-value for external walls has been increased to 0.26 W/(m2K) and a roof to 0.16 W/(m2K). However, adopting these as a minimum standard will not lead to a ‘pass’ for the building as a whole – this will be dependent on the energy calculation for the entire building.

As a guide, a ‘notational new dwelling’ (based on table 1.1) has been provided. In this example, an external wall will have a minimum u-value of 0.18 W/(m2K). Using a standard masonry cavity wall construction and typical mineral wool insulation, a minimum full fill cavity of 150mm would be required (dependant on supplied specification). This, in principle, increases the overall external wall thickness, impacting the usable internal space.

For roof insulation, a minimum u-value of 0.11 W/(m2K) has been adopted. Again, using typical mineral wool insulation and assuming a ‘cold roof’ construction, this would result in an insulation thickness of 400mm. Further, air permeability has also been assumed at 5 m3/(hm3), requiring attention to construction detailing and site supervision to ensure an acceptable result. The ‘notational new dwelling’ approach still assumes the installation of a PV system and WWHR (wastewater heat recovery) which will add significantly to the build cost for the project.

In order to avoid the use of costly renewable energy sources, a ‘fabric first’ approach may still be used, however, it would be necessary to significantly exceed the assumed values within the ‘notational new dwelling’, which in turn impacts on construction costs and usable space. Advice would need to be sought from a qualified energy assessor when carrying out the calculations.

As previously, the minimum standard for an extension to existing dwellings are lower than the ‘new build’ standards, although significantly increased over the previous Approved Document L. For example, the  u-value for walls has been increased to 0.18 W/(m2K) and a roof to 0.15 W/(m2K) compared to a u-value of 0.28 W/(m2K) and 0.18 W/(m2K) respectively.  

The amended document is a leap forward in terms of energy efficiency, leading to lower running costs for homeowners and reduced CO² production. However, this will lead to increased construction costs for the industry.

If you would like to discuss your project or property please contact our Architectural team on 0333 920 2220.



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