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Modernist EnerPHit Plus

Location: London
Completion Status: 2022 Occupancy: Since Oct 2021
Architect: RDA Architects Consultant: Passivhaus Consultant: Ecospheric, Structural engineer: Michael Baigent Orla Kelly Ltd
Contractor: PJS Building & Maintenance Client: Private client
Certification: June 2022 Certifier: MEAD Consulting
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2023 UK PAssivhaus Awards FinalistA 1960s modern concrete London designer pad gets a sensitive low energy makeover. Finalist in the 2023 UK Passivhaus Awards residential retrofit category.

Originally designed by architect Michael Blackstock, the 'Modernist'  has undergone an EnerPHit Plus retrofit makeover.  Passivhaus retrofit standards were implemented to allow the home to face the challenges of the future and future-proof the house against rising energy bills. This home now uses 88% less energy than an average UK home. 


Designed by PHT member RDA Architects, 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. 


Key stats

  • ConstructionMasonry

  • Form factor: 3.06

  • TFA:  159 m2 

  • Completed: 2022

  • Certified: EnerPHit,  2022

Modernist EnerPHit Plus: site plan   I   RDA architects

The house needed extensive repair works addressing air leakages and damp, but the the client was keen to retain many of the original features of the modernist 1960s aesthetic. The building's reinforced-concrete structure presented difficulties since it was hard to know the condition of the structure, and where the pre-stressed areas would be, until the building work was underway. 

Modernist EnerPHit Plus   I   RDA Architects/ Tim Soar Photography. Quote:

The three-storey property was originally designed in the ‘upside-down’ style , with an open-plan living space and terrace sitting above the first-floor bedrooms while the ground floor contained a garage and utility area. The retrofit involved a reorganisation of the layout, including replacing the groundfloor parking area with a large welcoming lobby leading to a private study and a bedroom with ensuite, alongside a utility and plant room. The Master bedroom and two further bedrooms are on the first floor, with the living space remaining on the third floor. Distributing daylight and heat from the hotter suntlit top floors through to the darker cooler bottom floors was a challenge.

Modernist EnerPHit Plus Before & After

To achieve EnerPHit Plus requirements involved careful consideration of how to introduce the airtightness to the existing building fabric without affecting the overall appearance of the existing house. There were also challenges about how to resolve thermal bridging between the new triple glazed windows and the existing walls. 


Modernist EnerPHit Plus   I   RDA architects. Quote:

Modernist EnerPHit Plus - RDA architects



Different wall build-ups (using internal or external wall insulation, such as EcoCork lime plaster, ThermaLine render or wood-based Steico insulation)  were needed depending on the orientation of the building. The outside of the building was fully re-rendered, alongside making good windowsills with leaking flashings. The project team aimed to retain as much of the existing structure and materials as possible, including the reuse of decommissioned pre-existing underfloor heating pipes. 


Balcony build-up. Image credit: RDA Architects  Roof build-up. Image credit: RDA Architects 


Modernist EnerPHit Plus, Construction   I   RDA Architects Modernist EnerPHit Plus, Window insulation   I   RDA Architects Modernist EnerPHit Plus, external wall insulation   I   RDA Architects



Overall U-values

Floor:  0.128 W/m2K

Floor insulation board on concrete floor. 

Modernist EnerPHit |  Image credit: RDA Architects/ Photographer Tim Soar

Wall :  0.163  W/m2K

External wall insulation board finished with cork lime plaster render.

Roof:  0.088 W/m2

Phenolic board Insulation, insulated plasterboard, pine cladding

Further information can be found at the International Passivhaus Database listing


Building performance

The house's renewable energy systems meant that the project attainied EnerPHit Plus certification. The house switched to all electric heating using an air source heat pump and underfloor heating. Solar PV panels, generating 7.8kW, were integrated with a high capacity battery storage system. 

The project team had to pay close attention as to how to integrate the air source heat pump with the solar PV panels and hot water storage, to ensure the most efficient energy output to the heating system at minimal demand from the grid. As well as replacing the roof, a new roof was created to include solar panels to the south side, with PV and evacuated tubes.

Predicted energy performance

Space Heating  Demand (≤ 25 kWh/m².a)           

25 kWh/m2.a

Modernist EnerPHit |  Image credit: RDA Architects/ Photographer Tim Soar

Heating Load 

14 W/m2

Primary Renewable Energy Demand (≤ 60 kWh/m².a)       

58 kWh/m2.a

Airtightness (≤ 1.0 ACH @ 50 Pa)

0.82 ACH @ 50Pa


Modernist EnerPHit Plus   I   RDA Architects
Modernist EnerPHit Plus - Monitoring data

Modernist EnerPHit Plus   I   RDA Architects/ Tim Soar Photography


Lessons Learned

  • Integrate solar shading in the local authority planning process at an earlier stage.
  • Stricter control on Mechanical and Electrical contractors who were in-experienced with Passivhaus EnerPHit
  • Ensure that the client is fully informed with Passivhaus options before planning is approved, as the Tesla Power wall was requested after planning.


Key team 

  • Architect & Passivhaus Designer: RDA Architects  

  • Contractor: PJS Building & Maintenance

  • Structural engineer: Michael Baigent Orla Kelly Ltd

  • Passivhaus Consultant: Ecospheric

  • Passivhaus Certifier: MEAD Consulting

Modernist EnerPHit |  Image credit: RDA Architects/ Photographer Tim Soar


Discover more about the project below via the awards poster & presentation.

2023 UK Passivhaus Awards: Modernist EnerPHit Plus - poster 2023 UK Passivhaus Awards: Modernist EnerPHit Plus - presentation
Modernist EnerPHit Plus   I   RDA Architects/ Tim Soar Photography

Further information

Modernist EnerPHit Plus

RIBA Journal: Retrofitting a 1960s modernist house to Passivhaus standards - 31 March 2023

Passivhaus Plus & Premium

Previous PHT Story: Old Timberyard gets new lease of life - 14 November 2022

Previous PHT Story: Passivhaus Mews II

Previous PHT Story: Chiswick Eco Lodge



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