AECB lifetime carbon modelling suggests that either of our two retrofit standards should deliver dramatically lower lifetime carbon emissions for homes - compared to not retrofitting. Over time we imagine two waves of retrofit happening, with some step-by-step projects progressing to full retrofit, depending on future policy and financial developments.


Summary and Webinar (via QR code)

Reducing the energy used to heat and power existing buildings, whilst making homes healthier and more climate-change resilient is a critical part of the UK’s necessary transformation towards a more responsible, ecologically, and socially sustainable society.

Our Retrofit Standard can be done step-by-step with a minimum first step called 'Step1' - This recognises the practical and financial challenges faced by ‘early adopter’ retrofitters in the absence of a working UK retrofit programme. They offer a pragmatic and flexible approach  to retrofitting existing buildings, and the new Approved Certifier scheme streamlines and strengthens the AECB’s approach to Quality Assurance.



Development of the Retrofit Standards by AECB CEO Andrew Simmonds


The energy and non-energy benefits of a deeper retrofit may justify adopting the full Retrofit standard for some projects, whereas the faster and lower capital cost Step 1 may be more appropriate for other projects. Completing a step 1 retrofit does not lock out later works to take the building to a cost-effective full Retrofit. The  Step 1 retrofit standard might also be called a ‘heat pump retrofit’ standard as it has been designed for a lighter fabric retrofit, effective ventilation and an electric heat pump. The full Retrofit standard allows retention of the existing heating system if required, and is designed for a deeper fabric retrofit.


CarbonLite Retrofit Step-By-Step

CarbonLite Retrofit


Social media and newspapers are flooded with myths about heat pumps.

Dr Jan Rosenow addresses the common misconceptions in a series of myth busting articles.

Click here to read the full series.

The truth about heat pumps

Coming in from the cold: Heat pump efficiency at low temperatures.  Further research by Jan Rosenow can be read here

For a case study of heat pump installation without deep retrofit read here


In order to maintain the integrity of the standards and ensure consistency of application, the AECB uses Approved Certifiers to confirm that projects have met the AECB CarbonLite Standards.

All our certifiers are AECB members, approved by us to carry out project certification.  Certifiers undertake regular AECB CarbonLite CPD.

  • The AECB Standards are based on the Passivhaus methodology, and certifiers use the Passivhaus Planning Package software (PHPP)
  • The certifier may choose to appoint a separate PHPP modeller as part of their certification service, or may do this in-house
  • Once modelled in PHPP, certifiers use the AECB CarbonLite LEBD Uploader software to collate project data and evidence and automatically upload the certified project to the Low Energy Buildings Database

To view a list of certifiers click here          

To become a certifier click here

 To review existing buildings that have been certified please visit the LEBD

Our other CarbonLite Standards