“It is widely accepted that retrofitting our existing buildings is absolutely critical if we are to achieve Net Zero. Around 18% of our annual national CO2e emissions come from existing homes – homes that will still be standing in 2050. 80% of 2050’s homes have already been built. It is also widely acknowledged that the retrofit challenge is monumental. Over one million homes every year for the next 30 years will need to be retrofitted. We cannot afford to retrofit them twice. But if we retrofit them well, we can enjoy many environmental, social and economic benefits.” Leti
Other than reducing CO2 emissions, retrofitting also reduces fuel bills, improves health, well-being and comfort.
Retrofit is essentially the thermal improvement of a building, incorporating energy efficiency measures. It may involve repair, renovation, refurbishment and/or restoration of the building and can be ‘deep’ – a whole house approach: upgrading the building fabric including improving insulation, airtightness and ventilation; or ‘shallow’ – a lighter touch, achieving minimal energy use reductions.
Retrofit can be carried out really well – reducing energy consumption and carbon emissions whilst also improving occupant comfort and health, but it can also be carried out really, really badly – failing to make the energy, carbon and financial savings anticipated and possibly also increasing the risk of other issues such as poor air quality, damaging moisture issues, fire and overheating.
We advocate the best practice approach of a whole building intervention where all aspects are considered holistically – the fabric, the services, renewables and the people who live there. The consequence of each measure taken is fully understood and the building is considered as a whole, rather than piecemeal parts. We take a fabric first approach, using natural materials as far as possible to improve fabric energy efficiency before implementing low carbon renewable technologies.
The Passivhaus Institute have an EnerPHit standard for retrofitting existing buildings up to Passivhaus standard where the criteria are slightly more relaxed than the new-build Passivhaus ones, to take into account existing building conditions and restrictions. If EnerPHit is not feasible, then the AECB have their own Retrofit Standard which is slightly more relaxed than EnerPHit. The Leti targets are useful, but they are ‘just’ guidance.
Retrofitting to no specific standard can bring with it problems such as under performance, overheating or air quality issues. The EnerPHit and AECB standards have specific criteria which are used as a measure of performance and a target to work to. Both EnerPHit and AECB Retrofit certification require a PHPP model. PHPP is a planning tool that considers a wide range of variable characteristics to provide confidence that the performance targets will be achieved at the end of the build process, by closing the gap between predicted energy use and real-world performance. Where the budget does not allow for complete implementation of measures, a whole house step-by-step approach can be arranged to ensure the avoidance of unintended consequences.
The Leti targets should perhaps only be used on smaller projects or where finances do not allow for a PHPP model.
A deep retrofit makes the most sense when you’re already considering extensive refurbishment works, or if the house is in a poor state of repair. If building elements already need repair or replacement then the additional costs and interventions associated with the retrofit will be less. If the building only needs part replacement then a step-by-step approach may well be the better place to work from.
Beyond this, a standard needs to be selected as a starting point, this will then be the benchmark as the design progresses. A PHPP model will need to be created for the existing building. The PHPP will allow us to make informed decisions about where best to make improvements and spend money. It helps to understand what cost and energy implications there are against various retrofit measures, and what alternatives might need to be considered.
Retrofitting is more complex and more challenging than a new building – many factors need to be considered and balanced against possible consequences. A skilled design and construction team are critical.
The ultimate benefit of aiming for certification of EnerPHit or AECB’s Retrofit Standard is the quality assurance that is demanded of the process. It ensures that the works are completed the way they were designed and that the performance targets are achieved as planned.
If you would like to discuss energy improvements to your home, please do get in touch. Alternatively, please fill in the enquiry form and we will get in touch to discuss your project in more detail. As always, we would be delighted to hear from you.