Passivhaus Affiliate

Modernist EnerPHit Plus

A 1960s 'Modernist' London home, originally designed by architect Michael Blackstock, 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.

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. 

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


Key stats

  • Construction: Masonry construction

  • Form factor: 3.06

  • TFA:  159 m2 

  • Completed: 2022

  • Certified: EnerPHit,  2022

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



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. 

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.

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

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. 

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

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

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


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 Plus, London. Image credit: RDA Architects/ Photographer Tim Soar


Other Certified Passivhaus projects by RDA Architects

RetroPHit House. Image © RDA Architects Dulwich Park Passivhaus Image © RDA Architects
Pitched Passivhaus. Image © RDA Architects



You may also like 

RIBA Retrofit Masterclass webinar series
Passivhaus retrofit Masterclass: on-demand
Passivhaus goes personal


Further information

Modernist EnerPHit Plus

Passivhaus Retrofit Masterclass lecture series: On-demand

Passivhaus Plus & Premium

Passivhaus & zero carbon

How to build a Passivhaus webinar series

Technical guidance: Good practice guide to airtightness

International Passivhaus Open Days: Summer 2023

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

RIBA Journal: Retrofitting a 1960s modernist house to Passivhaus standards31 March 2023

19th April 2023

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