Building Regulations Part L - Wales 

Building Regulations Part L1a  (Wales) Explained 

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

No new dwellings are exempt from energy efficiency requirements, 

Part L1a sets out five different criteria for building regulation compliance, which is applicable at different stages of the construction process. These include: 

1. The calculated CO₂ emission from the dwelling (Dwelling Emission Rate, DER) must be no greater than the Target Emission Rate (TER).

2. The building fabric and fixed building services should achieve minimum energy efficiency standards.

3. The dwelling should limit overheating from solar and other gains 

4. Dwelling construction and performance consistent with DER

5.  Information to enable energy-efficient operation of the dwelling should be provided to the occupier in an easy to understand format. 

Standard Assessment Procedure (SAP) assessments can provide a reasonable provision of compliance for all of the above criterion (air pressure testing could be required for criteria 4). A SAP calculation can determine the DER and TER, highlight design features critical for compliance, and can also check the risk of overheating.

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Building Regulations Part L1b (Wales) Explained 

This Approved Document provides guidance on how to comply with the energy efficiency requirements for building works to an existing dwelling.

The introduction of new building fabric to an existing dwelling (extensions), a change in energy status (unheated room becomes heated) or a material change of use (i.e. building now used as a dwelling where previously it was not), are all sections covered within Building Regulations Part L1b.

Part L1b, Extension Compliance 

U-Value Calculations can be used to determine if the new or even retained thermal elements which make up the extension achieve or better the standards established in Part L1b.

Extensions with large amounts of glazing

For a proposed extension with glazing that exceeds 25% of the total floor area of the extension, a whole dwelling calculation method (SAP Calculation) should be undertaken. This offers greater design flexibility as elements of the building design can be relaxed through 'compensating measures' elsewhere.

Part L1b, Conversions

Conversions resulting from a material change of use or a change of energy status will require an Energy Performance Certificate (EPC). Therefore an SAP calculation is advised in order to calculate the appropriate U-Values and compare these against the standards for new and retained thermal elements as well as controlled fittings (windows and doors) in Part L1b. 

SAP Calculations for Extensions >U-Value Calculations >

 SAP Calculations for Conversions >

Building Regulations Part L2a (Wales) Explained 

This Approved Document covers the energy efficiency requirements for new commercial/non-domestic buildings. 

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).

The Building's Primary Energy Consumption (BPEC) must also be lower than Target Primary Energy Consumption (TPEC).

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.

Large Extensions

Where the total useful floor area of a non-domestic extension is greater than 100m² and greater than 25% of the total useful floor area of the existing buildings, are considered large enough to fall under regulations for new non-domestic buildings. Therefore in order to comply they will require Part L2a SBEM Calculations. 

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Building Regulations Part L2b (Wales) Explained 

Part L2b highlights the energy efficiency requirements of existing commercial/non-domestic buildings.

This provides guidance for non-domestic building extensions, conversion and material changes of use.

Part L2b, Extension Compliance 

Larger commercial extensions need to follow the guidance set out in Part L2a of the Building Regulations and should be regarded as a new building.

Compliance for smaller commercial extensions can be achieved if the new thermal elements introduced with the extension meet or better the standards laid out in Part L2b.

SBEM Calculations can be undertaken to offer greater design flexibility with extensions, as elements of the design can be relaxed and compensated for elsewhere.

Part L2b, Material Change of Use/Conversion Compliance

When part of a building which was previously unheated becomes a space which is heated/cooled a change in energy status occurs, and thus a change in energy efficiency requirements. This also occurs when a building's purpose or use changes.  

SBEM Calculations can be used to achieve compliance in these scenarios by measuring the energy performance of the converted building. The software can also produce an Energy Performance Certificate (EPC) required for sale or let. 

Calculations for Extensions and Conversions

Related Links

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