Energy Efficiency Benchmarks
Any addition of insulation will help to reduce your energy usage. However, if you want to achieve a specific level of energy efficiency you will need to measure your home against one of several energy efficiency benchmarks. Two such standards are Passivhaus and AECB Carbonlite as described below. These standards are demanding (and can be expensive!) but achieving compliance with them will ensure ongoing low energy usage and will undoubtedly increase the value of your home.
There are case studies available online which mention costs of over £200,000 for whole-house retrofit projects and certification. You are unlikely ever to recoup these sorts of costs in energy savings alone, so undertaking one of these projects would typically be for those who are passionate about reducing their environmental impact moreso than purely saving money.
Passivhaus
German for “Passive House”, this is probably the best known and most demanding standard for energy-efficient housing. To be Passivhaus-compliant, a home will need insulation and airtightness levels far beyond those required by Building Regulations. The airtightness requirements are such that mechanical ventilation is essential to control moisture and maintain air quality.
In the words of the Passivhaus Trust - “Passivhaus adopts a whole-building approach with clear, measured targets, focused on high-quality construction, certified through an exacting quality assurance process.”
The five principles of Passivhaus design - insulation, airtightness, ventilation, windows and reduced thermal bridges.
Image credit - Passivhaus Institute
There is a related but slightly less stringent benchmark for retrofit projects known as EnerPHit, acknowledging that existing architecture and conservation issues may mean that meeting the Passivhaus standard isn’t always possible. However, even the EnerPHit standard is very demanding and will require a major investment to achieve.
More info - Passivhaus Trust
AECB
The Association for Environment Conscious Building “CarbonLite” standards include two retrofit-specific benchmarks called Level 1 and Level 2. Level 1 is the more basic standard and is primarily focussed in the installation of heat pumps. Level 2 is the higher standard, and is more concerned with upgrading the building fabric with insulation and airtightness. Somewhat confusingly, Level 1 seems to mandate the installation of a heat pump system whereas the higher Level 2 doesn’t.
In the AECB’s own words - “Our two Retrofit Standards – Level 1 & 2 - recognise 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.
“The energy and non-energy benefits of a deeper retrofit may justify adopting the Level 2 standard for some projects, whereas the faster and lower capital cost Level 1 may be more appropriate for other projects. Completing a Level 1 retrofit does not lock out later works to take the building to a cost-effective Level 2. The Level 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 Level 2 retrofit allows retention of the existing heating system if required, and is designed for a deeper fabric retrofit.“
The AECB also maintains the Low Energy Building Database which has some excellent case studies of successful retrofit projects.
More info -
RICS
In March 2024 the Royal Institution of Chartered Surveyors released its first “Residential Retrofit Standard”. This is primarily aimed at professional surveyors rather than homeowners, but there is some useful information for those undertaking retrofit projects.
More info - RICS Retrofit Standard
PAS2035
PAS 2035:2023 “Retrofitting Dwellings for Improved Energy Efficiency” is the British Standard for whole building retrofit and underpins most of the voluntary standards listed on this page. It takes into account the requirement of the entire building, both from a technical standpoint and considering factors like occupancy comfort. PAS2035 is closely related to the government’s Trustmark scheme.
More info -