Architecture studio Whittaker Parsons has completed Blythe Hill House, a retrofit and courtyard extension that transforms a 1970s end-of-terrace house in south-east London into a flexible, fully electric family home. Completed for a construction cost of £305,000, the project responds to a dark and outdated property with awkwardly proportioned rooms and poor environmental performance.
Located at the end of a suburban terrace, the house benefits from an unusually wide plot. Rather than adding a conventional rear extension, Whittaker Parsons introduced a 14-metre linear addition set perpendicular to the existing house, creating an L-shaped plan organised around a stepped courtyard garden. The arrangement brings more daylight into the home, improves privacy, and makes fuller use of the site’s width.
Living through the build
The project was shaped by a limited budget, a hands-on client, and a phased construction process. The family initially planned to purchase a separate garden room to live in during the works. Instead, Whittaker Parsons proposed incorporating this space into the extension, allowing the clients to remain on site while the house was being built.
The clients also completed much of the interior fit-out themselves, including the kitchen. One of the homeowners, a structural engineer, used the project to test low-impact construction strategies first-hand, with a particular focus on reducing upfront carbon.
A side extension and courtyard garden
The new addition runs along the side of the plot rather than extending directly into the rear garden. This move forms a stepped courtyard that follows the site’s slope and helps screen the garden from a neighbouring alleyway. A new porch creates a clearer entrance to the house, while the reconfigured ground floor connects the main living spaces to the courtyard extension.
The extension accommodates a utility room, shower room, playroom, and study/guest room. Originally conceived as temporary on-site accommodation during the build, this suite has become a permanent, flexible part of the house. With its own secondary entrance, it can adapt over time for guests, work, or multigenerational living.
Upstairs, the previously gloomy circulation space has been opened up as a pastel-coloured social landing, alongside a green family bathroom. Three bedrooms look towards the extension’s sedum roof, the courtyard, and the park beyond.
Low-impact construction and energy performance
The retrofit was designed around a lightweight, low-impact approach to construction. Working with structural engineer George Reed of Price & Myers, Whittaker Parsons used carbon modelling tools to refine the structural approach, halving embodied carbon in the groundworks. Rather than using conventional concrete footings and heavy masonry finishes, the extension was supported on screw piles and built with an exposed timber frame.
Bio-based and breathable materials were used throughout the new extension, including hempcrete, woodfibre insulation, hemp-lime plaster, lime render, and cork flooring. Together, these materials support the project’s focus on indoor comfort, low-toxicity finishes, and reduced embodied carbon.
The completed house is now fully electric, with an air-source heat pump providing heating and hot water, and rooftop photovoltaics supplying part of the household electricity. Alongside improvements to the building fabric, including triple glazing and loft insulation, these upgrades helped move the house from EPC D to EPC A.
Future flexibility also informed the construction strategy. New elements were detailed for future disassembly and reuse, while the extension’s loose-fit arrangement allows it to adapt as the family’s needs change over time.
Material character and everyday comfort
Blythe Hill House is rooted in the Swedish concept of lagom, meaning ‘just the right amount’. This idea informed an approach based on careful use of space, material, and budget. The palette of timber, hempcrete, and clay tile references the original facade while introducing a softer interior character.
Comfort, health, and long-term adaptability shaped the retrofit, from passive environmental strategies to material choices and the ability for spaces to change over time. The result is a family home that combines practical resourcefulness with a clear sense of care.
