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Lessons from retrofitting an Edwardian terrace
An Edwardian mid-terrace in Oxford has undergone a deep retrofit and extension to reduce primary energy use by 82%, writes Simon Chung, director at Sow Space
Simon Chung is director of Sow Space
An Edwardian mid-terrace in Oxford has undergone a deep retrofit and extension to reduce primary energy use by 82%, writes Simon Chung, director at Sow Space #UKhousingThe homeowner had a vision of a property that reduced energy consumption and improved the thermal performance of this very common type of home in the UK. They also wanted to ensure the property linked to the garden and introduced more natural light, so they could feel connected with nature in their main living space.
The project, in East Oxford, was successfully completed in July 2023. Here’s how we did it, and what we learned along the way.
Visualising the design process
The homeowner tasked my environmentally conscious architecture firm, Sow Space, with improving the energy efficiency of their home during the retrofit and extension process.
The existing house was a typical Edwardian mid-terrace: dark, narrow, difficult to navigate, cold and damp in the winter and hard to heat, with a poor connection to the outdoors. By remodelling the internal spaces and upgrading the building fabric, Sow Space has dramatically improved the thermal comfort and spatial coherence in what is now a bright, warm home.
Sow Space modelled the design in Archicad. This allowed us to create 3D images and walk-throughs which helped the homeowner visualise our design ideas. Archicad’s renovation filter allowed the homeowner to see the designs ‘before and after’, which was especially useful.
To take one example, we demolished the sunroom to open up the rear of the property. That kind of change can be hard to picture, so Archicad enabled us to easily communicate with the homeowner and explain design details and material choices to them.
Sustainability
Sow Space opted for wood fibre insulation and triple-glazed timber windows to improve the property’s thermal performance. This insulation has low embodied carbon and a high thermal mass, which helps keep the building at a consistent temperature throughout the year while reducing the retrofit’s carbon impact.
The client and planners wanted to preserve the street-facing facade of the Edwardian home so that the house didn’t look out of place in its setting. This introduced some challenges during insulation. We chose internal insulation for the front elevation, which meant the external view was barely changed, except for an added air source heat pump.
Meanwhile, external insulation was added around the side and back of the property. The heat pump acts as a visual reminder that this property isn’t a traditional Edwardian terrace, but a highly energy-efficient home.
Internally, the homeowner wanted to maintain the existing decorative features that gave the property its period character, such as fireplaces, cornices and picture rails. Using Archicad helped ensure the modernisation of the property was respectful to these Edwardian-period features and enabled the homeowner to visualise the changes before they were made.
The new kitchen was also constructed using natural and recycled materials with glue-free joints and finished with ultra-low VOC paint. Meanwhile, salvaged bricks from some of the original walls and a chimney breast in the property were used to create a new herringbone brick patio in the garden.
Retrofit measurement
Assessing the impact of the retrofit activity was important to the homeowner, so Sow Space provided additional services beyond the 3D designs.
The practice produced an environmental design report before the project started, so we understood the potential energy performance impact different retrofit activities would have.
The 3D designs in Archicad helped this process by ensuring that the correct dimensions of the walls, floors, doors and windows were inputted during the reporting process. Monthly energy meter readings, along with thermal imaging and temperature and relative humidity monitoring, were also taken to see how well the existing building performed before any work was done. In-person interviews with the homeowners also created a more opinion-based measure of the building’s performance.
Once the retrofit work was completed, the tests were repeated and the monitoring data was compared against the baseline. The retrofit work achieved an 88% reduction in the use of heating and hot water, and an 82% reduction in overall energy use within the home, which created significant financial savings for the occupants.
Relative humidity levels are now within the recommended 40-60% range, and overheating over summer is never more than 2%.
Yearly energy consumption per square metre was reduced by 83.2%, meeting the performance levels set out in both the LETI standard and the Passivhaus standard for existing buildings.
The homeowner told me: “We achieved a successful blend of the early twentieth-century original, up-to-the-minute green renovations and modern touches.
“When I think about what has been achieved, I am very grateful for Sow Space’s stewardship of it all.”
Simon Chung, director, Sow Space
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