Garden Room Extension at Culverden Road
An architect-designed garden room extension connected directly to a late-Victorian home in Balham. Replacing a poorly insulated conservatory, it brings Carolyn and David closer to the garden and the mature trees beyond. Careful coordination of the structure, glazing, roof and landscape allows a technically complex design to feel calm and natural.
Location: Balham, London Borough of Wandsworth
Property: Late-Victorian detached villa
Planning context: Culverden Road Conservation Area
Project: Attached, partially cantilevered garden room extension
Wider scope: Structural repair to the closet wing, bathroom alterations, internal joinery, rear entrance, garden coordination and side shed
Service: Full Architectural Service, including planning, technical design, tendering and contract administration
Completed: September 2020
More than a glass box
When Carolyn and David first contacted us, an ageing conservatory occupied much of the rear of their home. It was reached from the kitchen and hall through a small doorway and a series of steps, and its floor sat more than a metre above the garden. With limited insulation and extensive overhead glazing, it was uncomfortable in both winter and summer.
They wanted a room they could enjoy throughout the year, with generous light and views towards the garden and the trees of the common beyond. Just as importantly, Carolyn was clear that she did not want “a glass box”. We understood this as a wish to avoid a conventional rectangular contemporary extension that could have felt unrelated to the character of the house.
That short phrase became a useful design test. The new room needed to be modern, open and highly glazed, but it also needed to belong to this particular home. The result shows why an extension does not have to be a glass box.
The original conservatory was highly glazed but poorly insulated, with its floor more than a metre above the garden.
A garden room shaped by the house
The garden room's unique angles can appear spontaneous, but they were developed through a rigorous study of the existing building. Lines from the walls, roof forms and internal layout were extended into the new plan. These alignments shaped the room, opened views on three sides and allowed part of it to cantilever over the garden.
The roof was treated with the same care. Rather than glazing the whole surface, a predominantly solid, well-insulated roof helps the room remain comfortable through the seasons. A carefully positioned rooflight brings daylight further into the house, while bespoke glazing and a slender steel structure keep the garden-facing corners visually open.
The finished room may look effortless, but it was never accidental. Its character comes from a sequence of rational decisions about light, views, comfort, structure and the relationship between old and new. This is the same joined-up thinking we bring to garden room and house extensions for London homes.
The angled plan came from lines already present in the original house. The finished glazing carries those alignments into the garden room.
A project that evolved
The first concepts were presented in March 2014, followed by a developed scheme that June. Planning approval and the first tender followed in 2015.
During the design process, subsidence was identified in the closet wing, associated with a large tree in a neighbouring garden. The first tender assumed that this part of the house would be demolished and rebuilt. Combined with the complexity of the garden room, the cost was higher than expected, so the project paused while Carolyn and David pursued an insurance claim.
Following the insurance award, the scheme was resubmitted in May 2018. By then, the clients' thinking had also moved on. The internal joinery and stair were reconsidered, the ensuite floor and roof levels were adjusted, the rear entrance and side shed were included, and the developing landscape design needed to be coordinated with the building.
The structural strategy changed too. Instead of demolishing the entire closet wing, it was underpinned and selectively repaired. The project was tendered again in March 2019.
This was not a simple, uninterrupted route from sketch to construction. Each stage introduced new information that had to be understood without losing the central idea. The continuity of the architectural service allowed the design, planning history, structural repair, interiors and garden to be considered as parts of one project.
Carrying the design into the garden
Landscape designer Rebecca Heard joined the project as the revised scheme developed. The garden was not treated as a separate layer to be added after the building was complete.
The new walls, steps and paths were aligned with the garden room doors and its angled geometry. This carries the logic of the extension into the landscape and makes the connection more than a view through glass. The route out of the room, the change in level and the way people move through the planting were considered together.
The garden walls and steps continue the geometry of the extension into the landscape.
Bringing the pieces together
The apparent simplicity of the finished room depended on close coordination between many separate elements: the underpinning and existing masonry, the new steel frame, the multi-plane roof, bespoke glazing, opening windows, internal alterations and the landscape levels outside.
Each consultant, fabricator and contractor understood their own part of the project. The challenge was at the points where those parts met. A steelwork model, for example, could be correct within its own package and still need to be checked against the glazing, roof build-up, existing walls and the dimensions found on site.
The structure was therefore set out carefully on site with main contractor Christian Rauchegger, followed by a detailed review of the steel fabricator's drawings. The base-plate drawing went through ten revisions as dimensions, connections and spatial relationships were tested and clarified before fabrication. This was not evidence that any one party lacked expertise. It showed how demanding the geometry was, and why the interfaces could not be left to resolve themselves.
Christian and Studio CMA worked through the questions together, checking critical dimensions and resolving potential conflicts before they became expensive physical problems. That is a practical example of how we approach complex home projects: specialist knowledge matters, but someone must also maintain an overview of how every part affects the others.
The apparent simplicity of the room depended on close coordination between the existing building, steel frame, roof and bespoke glazing.
Managing construction through Covid-19
Construction began in September 2019 and was originally programmed to finish in May 2020. The outbreak of Covid-19 disrupted the programme, supply chains and normal ways of working.
Studio CMA remained involved as architect and contract administrator, maintaining communication, reviewing work and helping the team respond as circumstances changed. Although the programme extended, practical completion was reached on 24 September 2020. Christian later confirmed that the project had no cost overruns.
“The project went according to plan with no cost overruns. I really enjoyed working with CMA and would definitely like to work with them in the future.”
Christian Rauchegger
Director, JCR Projects Construction Ltd
Nothing ordinary
The outcome is a room that feels close to the activity of the kitchen but offers a quieter place to sit, look out and experience the changing light. The garden and the mature trees beyond form part of daily life throughout the year.
“There is so much about this project that we are delighted with. We love the magical light and space that it has given us, with wonderful views of our garden and the trees of the common behind, making it feel like being in the countryside.
“There is nothing ordinary about this project. Our garden room is full of amazing angles and triangles of different heights, from the doors and windows to the ceilings and skylight. It is a lovely space to spend a relaxing time in, but still close enough to the buzz of our kitchen.”
Carolyn and David
Balham, Wandsworth
Project team
Clients: Carolyn and David
Architect and contract administrator: Ciarcelluti Mathers Architecture
Main contractor: Christian Rauchegger, JCR Projects Construction Ltd
Structural engineer: Robbie Belmore, Milk Structures
Landscape designer: Rebecca Heard, Fineline Garden Design
Specialist glazing: Cantifix
Completion: September 2020
Press and publications
Good Housekeeping
Planning a complex extension or renovation?
A builder, engineer or specialist contractor can understand their part of a project extremely well. Someone still needs to understand how all the parts affect one another.
Careful architectural coordination helps resolve the gaps between separate packages before they become physical and expensive.
If you are considering a garden room extension, renovation or structural alteration to a London period home, we can guide the project from the first ideas through planning, technical design, tender and construction.