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Green Sky Thinking: Retrofit in conservation areas with Marks Barfield

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Post-occupancy monitoring demonstrates the potential for savings in a Victorian retrofit


Priory Grove, retrofit and extension in a conservation area. Marks Barfield Architects

The renovation of existing housing stock in conservation areas was the talking point at Marks Barfield Architects’ breakfast presentation at their bright and airy offices near Clapham Common. Since over a quarter of the UK’s carbon footprint is produced by its 26 million homes and half of all UK conservation areas are located in London, this was an apt topic to begin the second day of Open-Ciy’s Green Sky Thinking programme. Julia Barfield presented the practice’s recent work at 63 Priory Grove, a Victorian retrofit and extension project in Stockwell’s Larkhall Conservation Area.


63 Priory Grove - existing


Priory Grove - after renovation and extension

The client’s brief was to transform a Victorian end of terrace home built in 1842 into a contemporary sustainable family home fit for the 21st century. Sustainability consultant Loren Butt worked with Marks Barfield to develop the scheme. One of the initial design activities was to define and categorise possible energy saving measures and develop a graphic representation which could be shared with the client and the project team.

Design studies were undertaken to explore what would be most appropriate for the site. To respect the neighbouring buildings, a rear extension was considered preferable to extending sideways. A light well connects old and new, bringing daylight deep into the plan. The final design incorporates a light well, maximises use of thermal mass and stack ventilation, as well as mechanical heat recovery, a sun pipe, LED lighting, and sedum and wildflower roofs.

Period materials and details were simply replicated, stripping back ornamentation while retaining the look of the front elevation. Reclaimed stock bricks to match existing were sourced for the extension, which is clad in breathable, lime render. Timber throughout the house is oak, sourced from sustainable European forests. New double glazed timber sash windows were supplied by a small joiner in Kent.

Bespoke Portland stone louvres allow secure nighttime ventilation, with additional air movement provided by Passivents.



A highly insulated envelope and passive design measures including carefully positioned thermal mass, low-e glazing and stack ventilation mean that the house is predicted to perform 60 per cent better than building regs.

The only external energy supply is electricity. 75% of extracted heat is recovered, and the heating load is boosted with an air source heat pump. PV panels were considered, and may be added in future. Conservation require them to be fitted horizontally, and calculations demonstrated that only 10% of efficiency would be lost compared to a conventional 45° angle installation.


Since its completion in 2010, Priory Grove has undergone rigorous measurement and post-occupancy evaluation via 5 separate meters located throughout the property. After two years of monitoring, Priory Grove averages an impressive 30kg CO2/m2/year.

During the Q&A, issues such as the validity of BREEAM as a measuring tool, the political environment of building retrofits and specific technical detailing dominated the discussion. The morning concluded with a summary of how architects can comply with building regulations in retrofit projects while still pleasing the conservation officer. Overall, this was a very informative and engaging event.



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