Building Regulations Part L

Building Regulations Part L1a Explained

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

Those responsible for the building work (developers, builders, designers, agents, etc) must ensure that the work complies with the requirements provided within the Part L1a approved 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 CO2 emissions and requires a dwelling to achieve a Dwelling Emission Rate (DER) equal to or lower than the Target Emission Rate (TER) established before the property is built. More about DER/TER here .  

Standard Assessment Procedure SAP calculations are used as the approved methodology to calculate the energy performance of dwellings 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.

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 "Over-glazed Extensions"

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 CO2 emission rate does not exceed the emission rate of the same dwelling with a notional extension.