03 Aug 2023

EnerPHit: Turning Ordinary Homes into the Extraordinary

If you love where you live and want to radically reduce your energy bills, make your home more comfortable and help tackle the climate crisis, then undertaking a Passivhaus retrofit (EnerPHit) could be for you.


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The last few years of lockdown and the energy bill crisis have woken us all up to the impact of draughty and leaky homes on our quality of life, health and wellbeing. Passivhaus is an international building standard that dramatically reduces buildings’ heating energy requirements while also creating excellent indoor comfort levels.

The building physics behind Passivhaus can be applied to any building – although it is often more challenging for existing buildings where the orientation, structure, shape and amount of glazing are already predetermined. To address this, the Passivhaus standard offers a retrofit standard called EnerPHit, which takes these constraints into account and relaxes criteria to reflect this.

EnerPHit is still a very demanding standard and will typically result in a building that outperforms a new-build property both in terms of energy and comfort. Like the Passivhaus standard for new builds, it includes requirements for high levels of insulation, airtight fabric, high-performance windows and doors, reduced thermal bridges and mechanical ventilation heat recovery (MVHR).

The Passivhaus retrofit approach can be applied to homes and buildings from all eras and construction types. This year’s UK Passivhaus Awards 2023 included four finalists in the residential retrofit category, showcasing the variety and versatility of the EnerPHit approach. A ‘70s mid-terrace townhouse, a derelict barn, a suburban detached house and a ‘60s Modernist concrete London home were all given the Passivhaus retrofit treatment to become certified EnerPHit (or EnerPHit Plus*) projects, achieving proven long-term comfort and energy savings.

The retrofit strategies included a mix of using external or internal wall insulation to provide continuity of thermal insulation around the existing homes. The barn conversion was achieved using an insulated timber-frame box within the stone building. As well as the fabric-first Passivhaus elements, the shortlisted projects added renewable energy generation to their homes, with three of the four projects shortlisted achieving EnerPHit Plus* certification, which means that the homes produce as much energy as occupants consume, with the energy generated coming from renewable sources and providing enough energy to operate the building throughout the whole year.

Interestingly, the winning project in the residential retrofit category is also the UK’s first certified phased EnerPHit project. Step-by-step EnerPHit is a route to certification that offers a staged approach to retrofit undertaken in several phases over time to help with budgeting and enable occupants to continue living in a property while the work is being carried out.

Bowman’s Lea EnerPHitAwards residential retrofit category

A phased retrofit of a three-storey ‘70s mid-terrace townhouse, Bowman’s Lea is the UK’s first certified step-by-step EnerPHit, providing a valuable model for a more gradual approach to deep retrofit. Meticulously self-built, the retrofit utilises bio-based materials where possible, such as cork internal wall insulation. Knowledge transfer has been a huge part of the retrofit, helping to spark local neighbourhood retrofits. Open days have enabled people to see first hand what a low-energy retrofit entails. The focus on engagement and sharing has inspired six neighbours to also retrofit their homes and influenced the wider local community, including the setting up of Retrofit Action For Tomorrow, which helps schools to undertake deep retrofits.

Harpenden EnerPHit PlusShortlisted in the 2023 UK Passivhaus Awards residential retrofit category

A suburban ‘70s detached four-bed in a conservation area has been revived by an EnerPHit Plus upgrade, slashing fuel bills. Striving for a Passivhaus retrofit was driven by ambitious and environmentally-conscious clients who were keen to give their Hertfordshire property a new lease on life through a holistic retrofit and, in the process, use their experiences to increase awareness among others. The project utilises a fabric-first approach to drive down energy demand but also includes additional renewable energy generation to achieve the EnerPHit Plus certification.

Modernist EnerPHit PlusShortlisted in the 2023 UK Passivhaus Awards residential retrofit category

Originally designed by Architect Michael Blackstock in the ‘60s, the ‘Modernist’ concrete London townhouse has undergone an EnerPHit Plus retrofit makeover. Passivhaus retrofit standards were implemented to allow the home to face the challenges of the future and futureproof the house against rising energy bills.

The house needed extensive repair works addressing air leakages and damp, but the client was keen to retain many of the original features of the Modernist ‘60s aesthetic. The ambitious project strived to maintain the existing structure to extend the building’s life by another 100 years while also combining the original design aesthetic with a contemporary approach.

Shepherds Barn EnerPHit PlusShortlisted in the 2023 UK Passivhaus Awards residential retrofit category

Nestled in a valley in County Durham, Shepherds Barn is an ultra-low-energy barn conversion and retrofit. The North East’s first certified EnerPHit project, it achieves an impressive airtightness result of 0.18 ACH @ 50 Pa. An airtight timber-frame structure was built inside the original stone barn building allowing the project to achieve the EnerPHit standard. The project has since been re-certified to EnerPHit Plus certification status in February 2022, after extra renewable energy capacity was added.

Challenges on the project included working within the constraints of the existing barn building, issues around planning, structural instability and moisture issues, all had to be addressed.

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