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Is a good EPC rating a guarantee of good energy performance?

Rightly or wrongly, there has been a concern that design criteria for energy efficiency, which are used by energy assessors as the basis for energy performance certification, have not always carried through to the final construction of projects.

New requirements in force with the introduction of Part L 2010 Building Regulations seek to address the perceived gap between design aspirations and final specifications. For example:

  • U-values and heating system efficiencies are to be shown on Energy Performance Certificates
  • There are increased requirements for the number of air pressure tests on a development
  • Cold bridging details will be considered individually rather than using a single parameter

How will complying with Part L 2010 affect our clients?

Compliance with  Part  L  2010 must  be  demonstrated  at  several  stages  during  the construction process. For instance, the Approved Document for Part L1a states that CO 2  calculations must be presented “ no later than the day before work starts ” (page 13, Regulation 20D). This means that design stage CO 2  calculations will become mandatory.

There  is  a  question  as  to  how  this  requirement  will  be  interpreted.  Initial  advice  from  energy assessment accrediting bodies such as National Energy Services (NES) is that finalised design stage calculations  will  be  required  for  every dwelling  prior  to  work  starting.  This  implies  that  Part  L calculations should be taken as far as the interim Predicted Energy Assessment (PEA) Certificate.

However, compliance with Regulation 20D will be at the discretion of building control. It may be that in practice draft calculations for a range of ‘representative’ plots only are deemed to be acceptable. That would overcome a problem we foresee of construction work being well underway prior to the freezing of final designs.

As well as satisfying Building Control bodies, Part L1a documents are now a part of the paper trails for Planning Approval, Sales and Marketing and Code for Sustainable Homes Certification. The trail of evidence now required to certify homes for energy performance is certainly more robust and subject to more scrutiny than previously. Managing the implications of this evidence trial will require time and early attention.