Part L1A and L1B Building Regulations

on Tuesday, 24 April 2012.

Green Box Associates are licensed NHER and STROMA SAP 2012 assessors and can support your new build project to comply with Approved Documents Part L1A (new build) and Part L1B (existing dwellings) of Building Regulations and issue energy performance certificates (EPCs).

Part L of Building Regulations covers the conservation of fuel and power and sets minimum standards for building fabric and services.

Compliance with Part L1A requires a model of the building to be constructed in approved software by a licenced assessor.

Greenbox Associates can assist by:

Part L1A

  • Modelling proposed dwelling(s) in approved software
  • Advising on design and specification
  • Undertaking U value calculations to the requirements of BRE 443 and ISO 6946
  • Model thermal bridges using PsiTherm software to the requirements of BRE 497 and ISO 10211
  • Advise on suitable renewable technologies for your site
  • Provide paperwork to demonstrate compliance for building control
  • Issue EPCs for new dwellings
  • Provide reports to support planning requirements


 Compliance with Part L1B can be demonstrated in three ways

Part L1B

  1. The reference method- where thermal elements (including glazing areas)  and controlled fittings and services meet the requirements of Part L1B
  2. Area-weighted U values method where some U values and glazing areas do not meet the requirements of Part L1B, and others exceed, calculations can be undertaken demonstrate compliance
  3. Whole dwelling calculation method is a more flexible approach and requires modelling of the existing and proposed dwelling. This is often the case for conservatory extensions where glazing areas exceed Part L1B.

Greenbox Associates can assist with all three of the above methods and issue supporting paperwork for building control