Demonstrating compliance with Part L- Conservation of Fuel and Power of the Building Regulations is achieved through comparison of the dwelling with a Notional Building across two compliance metrics, the Emission rate and Fabric Energy Efficiency rate. This is expected to expand to three compliance metrics with the upcoming uplift to Part L of the Building Regulations to include the Primary Energy Rate as well.
But what is the Notional Building that produces the targets for these compliance metrics, and how does it impact the design choices for new-build homes?
The Notional Building is essentially a benchmark building, with the same geometry as the actual dwelling, but follows an ‘elemental recipe’. This ‘recipe’ is a specification of factors that influence the energy efficiency of a dwelling. The factors included, and the values used to define the notional building currently used for Building Regulations can be found in Appendix R of SAP 2012. Technically, if the actual dwelling is constructed entirely to the specification of the Notional Dwelling, it will meet the TER and better the TFEE rate, thus passing Criterion 1 of Part L1A of the Building Regulations.
In reality, you are highly unlikely to purely follow the specification of the Notional Dwelling just to comply with Part L: economic and aesthetic factors are usually much more important considerations to both the builder and end-client than achieving the highest energy efficiency possible. With the interim Part F, Part L and Overheating regulations due to be published in December 2021, the specification for the notional building will change.
The interim update to Part L of the Building Regulations will see an improvement on the notional building by reducing the U-values of the building elements, thus requiring a more highly insulated building than before. Further to this, the notional building will now have a PV system and also have instantaneous waste water heat recovery (WWHR) systems under all showers with 36% recovery efficiency. As a result, the typical mains gas boiler specification for new builds will likely need renewables added in order to comply.
Essentially, the new notional building will drive the reduction in emissions and improvement in energy efficiency desired by the interim update to Part L by imposing higher standards of thermal performance combined with energy-saving technologies and solar panels as the target for our actual buildings.
Pushing for ever-increasing energy efficiency through higher levels of insulation and reduced air permeability is absolutely necessary, but the impact this may have on other aspects of buildings must be carefully considered, such as ensuring adequate ventilation, and preventing overheating to name but two.
The specification for the new Notional Building is presented in Appendix R of SAP 10.1, as seen below:
Article published 22/07/21