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Understanding Part L Building Regulations

April 6th 2014 will see the introduction of the new Part L 2013 Building Regulations. Below are the key changes.

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  • A 6% reduction in CO2 from 2010 levels
  • Reduction is an aggregate figure across the housing mix so those dwellings with more fabric, such as detached houses, will be required to reduce more CO2 than a mid floor flat
  • As second target to hit in SAP based on the fabric performance of the dwelling called TFEE (Target Fabric Energy Efficiency) based on energy use
  • When a SAP for Part L 2013 is carried out both the traditional carbon target TER (Target Emission Rate) and the TFEE must be passed.
  • There is a new notional building for 2013 and the specification details appear in ‘Section 5: Model designs’. If the specification is followed the dwelling will pass the SAP – allowing a simple recipe approach to Part L compliance for the first time
  • The fabric U-value requirements of the notional building are:

              Wall 0.18

              Floor 0.13

              Roof 0.13

  • No changes in limiting fabric U-values


  • A 9% reduction in CO2 from 2010 levels
  • A wider range of notional buildings have been defined for top-lit, side-lit (heated only) and side-lit (heated and cooled) buildings
  • The notional building air permeability parameters have been further defined by the gross internal area of the building. The larger the building, the easier it is to achieve a good level of air tightness.
  • The notional building details appear in ‘Section 5: Model designs’ and if the actual building is constructed entirely to this specification it will pass the TER requirement
  • No changes in limiting fabric U-values

Existing buildings

  • No changes to requirements over that in the current Part L 2010 regulations when constructing loft conversions or extensions
  • Consequential improvements have not been implemented