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 >