Building Regulations Part L - England

Building Regulations Part L1a Explained 

Approved Document Part L1a highlights the requirements for energy efficiency compliance of new build dwellings.

Individuals responsible for the building work (developers, builders, designers, agents etc) must ensure that the work complies with the requirements provided within this document.

This document establishes a different criteria for demonstrating building regulation compliance both at design stage and after the dwelling is built.

The main compliance target is based on carbon emissions and requires a property to achieve a Dwelling Emission Rate (DER) equal to or lower than the Target Emission Rate (TER) established before the property is built.  

Standard Assessment Procedure (SAP) calculations are used as the approved methodology to calculate the energy performance of a building at both design and 'as built' stage.

If the SAP calculations comply with Part L1A, this will demonstrate that the dwelling has been designed and constructed to the appropriate standards.

SAP Calculations for New Build >

Building Regulations Part L1b Explained 

Approved Document Part L1b highlights the requirements for energy efficiency compliance of existing dwellings.

Part L1b covers the energy efficiency requirements of building work, to or in, an existing property (extensions/conversions). 

The document looks at energy efficiency requirements of building extensions, as wells as 'Material Change of Use' (barn/garage conversions), and also a change to a buildings energy status (unheated building/space becomes thermally conditioned).

The introduction of new thermal elements, will result in energy calculations to ensure the energy performance of the converted property is no worse than if the house had been improved.

Part L1b, Extension Compliance 

U-Value Calculations can be used to demonstrate that the new thermal elements introduced with the extension meet or better the U-Value standards provided in Part L1b.

Extensions with excessive glazing accounting for more than 25% of the total extension floor area will require SAP Calculations in order to demonstrate that 'reasonable provision' has been undertaken to comply with regulations.

Greater design flexibility can also be achieved through a whole dwelling calculation method, where SAP is used to show that the calculated carbon emission rate does not exceed the emission rate of a dwelling with a notional extension. 

SAP Calculations for Extensions > U-Value Calculations >

Part L1b, Conversion Compliance

If part of a building is converted from being unheated to heated, or its use or purpose is changed, then Conversion calculations may be required to demonstrate compliance. These calculations are undertaken within SAP Software, which is also able to produce a legally valid New Build Energy Performance Certificate (EPC).

 SAP Calculations for Conversions >

Building Regulations Part L2a Explained 

Approved Document Part L2a highlights the requirements for energy efficiency compliance of new buildings other than dwellings (commercial/non-domestic buildings).

Individuals responsible for the building work (developers, builders, designers, agents etc) must ensure that the work complies with the requirements provided within this document.

This document highlights the different criteria for demonstrating building regulation compliance, both at design stage and after the building is built.

The main compliance target is based on carbon emissions and requires a property to achieve a Building Emission Rate (BER) equal to or lower than the Target Emission Rate (TER) established before the building is built.

Simplified Building Energy Modelling (SBEM) is the approved methodology used to calculate the energy performance of a commercial building at both design and 'as built' stage.

This coupled with Air Permeability/pressure testing after the building is constructed, can provide Part L2a compliance for a newly constructed commercial building.

Click below to find out more about SBEM Calculations and how we can help you comply with Part L2a:

SBEM Calculations >

Building Regulations Part L2b Explained 

Approved Document Part L2b highlights the requirements for energy efficiency compliance of existing buildings other than dwellings (commercial/non-domestic buildings).

Part L2b covers the energy efficiency requirements of building work, to or in, an existing commercial building (extensions/conversions). 

The document looks at energy efficiency requirements of building extensions, 'Material Change of Use' (office to school etc), and also a change to a building's energy status.

Part L2b, Extension Compliance 

Similar to extensions to dwellings, U-Value calculations will likely be required to demonstrate that the new thermal elements meet the standards in Part L2b.

Larger commercial extensions of more than 100m² with a floor area greater than 25% of the existing building will require an SBEM Calculation in accordance with Part L2a of building regulations, as it is large enough to be considered a new commercial building.

Extensions less than 100m² may still require an SBEM calculation, if the proposed extension has a large amount of glazing. In this case, an energy model will be created to demonstrate that the proposed building extension emits less carbon than a notional extension.

U-Value Calculations  >SBEM Calculations for Extensions >

Part L2b, Conversion Compliance

A building which has a 'Material Change of Use' or 'Change of Energy Status' will require an SBEM conversion calculation in order to demonstrate that the CO₂ emissions are no worse than if the building had been improved.  

SBEM Calculations for Conversions >

Related Links

SAP Calculations > SBEM Calculations >