30th May 2026
Retrofit and extension of 19thC London townhouse
Newsletter May 2026
We have been busy in the studio since our last newsletter, with several exciting projects gathering momentum. We lead with the completion of a house in London, where craftsmanship and a focus on nature are at the heart of our design.
Meanwhile, in Doncaster, our new healthcare project is taking shape (which you can read about in more detail below) and at Cagni Williams Energy we have been hard at work introducing a low carbon future for a large private residence, including installing a ground-source heat pump as part of a move towards long term adaptability.
We are delighted to be the architects of a project turning heads in Wandsworth, a low-carbon Edwardian home in South London, with a bold new Corten steel and glass gallery extension. Every detail tells a story from the wildflower roof to the air source heat pump and from the bespoke white oak joinery to the curved glazing. We hope you enjoy the tour.
A Low-Carbon Transformation - Light, Nature and Craftsmanship
Our clients wanted something deceptively simple: more light, a stronger connection to the garden, and a home that no longer weighed on their conscience. What followed was a complete rethinking of a London home, from the bones of its structure to the wildflowers on its roof. The result is a home that feels simultaneously rooted in its Edwardian past and entirely of the moment: warm, light-filled, low-carbon and designed for modern life.
"We wanted our home to feel like it belonged to us — to our values as much as our family. Cagni Williams understood that from the very first conversation." - the client
A Project Born from Friendship and Shared Values
The homeowners had a clear sense of purpose. Aware of their environmental impact, the family wanted their home to reflect their commitment to sustainability. At the same time, the ground floor was dark and the garden was not visible from the living rooms.
From those twin ambitions — carbon consciousness and a longing for light — the entire project took shape. The Edwardian front rooms and entrance were carefully preserved, keeping the character and street presence that gives the area its identity. But moving through the hallway, everything changes.
The Corten Steel Gallery - Where Inside Meets Garden
The centrepiece of the project is the extension, replacing an old conservatory with a contemporary light filled gallery. We specified Corten steel which is a wonderful material that develops a rich, oxidised patina over time, and has a quality that feels simultaneously ancient and thoroughly contemporary.
The gallery is a long, light-filled room that acts as a transition between the kitchen and dining space and the garden beyond. Full height glazing floods the interior with daylight at every hour. In the evening, the Corten glows warmly against the planting. Functionally, the gallery serves as kitchen extension, and informal TV and sitting area — the gravitational centre of family life.
The expressed steel structure is left honest and visible, framing views of the garden and giving the room a quiet industrial poetry that contrasts beautifully with the warm timber joinery and white-painted Edwardian bones of the original house.
Wood & Joinery - Warmth Woven Through the Home
The expressed steel structure works in dialogue with solid white oak joinery throughout the ground floor. Ceiling joists are left exposed in the open-plan kitchen and dining area, creating rhythm and texture and anchoring the space with natural materials.
The new kitchen combines generous storage, bespoke cabinetry and conceals the guest WC tucked neatly under the stairs. Upstairs, the refurbished first-floor garden room has been given new life, with joinery that frames the view into the garden.
This is a quieter space, but one with a clear connection to the green roof below — a room in which the seasons are always visible. See the video with the shutters opening and closing, to give flexibility to separate the Edwardian home and dining snug from the open Gallery.
Energy & Environment - The ASHP, Green Roof and Living Systems
Expertise from Cagni Williams Energy contributed to the successful design.
The environmental performance of the home was a priority not an afterthought. The entire house is now powered by an air source heat pump (ASHP) installed in the garden, replacing the previous gas-fired boiler. Combined with underfloor heating in the extension, the home achieves an improved level of thermal comfort which is even, consistent warmth with dramatically lower carbon emissions. Ventilation was designed alongside the heating strategy especially in the Gallery where there was a risk of overheating in summer.
The green roof over the gallery extension is planted with native wildflowers, providing insulation, managing rainwater runoff, supporting biodiversity, and — not least — offering a beautiful view from the first-floor terrace and garden room above. It is a detail which rewards you every time you look at it.
The wildflower roof changes with the seasons. In June it is extraordinary. It is a reminder that good environmental design and beauty are not in tension — they reinforce each other.
Scaling the Approach - from Terrace to Larger Homes
The principles that shaped the terraced house in South London translate to larger properties. Greater scale offers even more to work with. A Corten and glass gallery extension anchors a generous rear elevation just as confidently on a detached Victorian or inter-war house as it does on an Edwardian terrace. The expressed structural language of steel and timber scales up without losing character. Bespoke joinery can be extended to handle greater storage and integrate technology and devices.
The green roof and wildflower planting strategy are even more impactful on larger projects — both for biodiversity and for the delightful views from upper rooms and terraces. On the energy side, the calculations improve significantly on larger projects. Where floor area is larger, underfloor heating delivers greater comfort gains.
Where extensive grounds are available, a Ground Source Heat Pump (GSHP), which draws on the thermal mass of the earth, is a viable option. With Cagni Williams Energy, we are putting this approach into practice on other projects.
We are working on a large residential property in Buckinghamshire where the grounds allowed us to install a GSHP as the primary heat source, and see below for more about the masterplan for a NHS Trust in Yorkshire to meet government's Net Zero target.
Oh, and our clients are so happy that we are about to start a new project for them– so watch this space!
So if you own a single property and have been inspired by what we achieved in Wandsworth, we would love to talk!
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