James Alder Architects apartment extends with semi-vaulted garden room

The roofline of this one-story, side and rear extension is in line with the internal circulation requirements, allowing a transition from the elevated level of the ground floor of the existing property to the lower level of the garden beyond.

Key to the project was the retention and extension of a large brick wall that had previously supported a symmetrical pair of outbuildings and dilapidated latrines for sloping roof gardens. It had already been partially demolished prior to the start of the project with the original fabric and structure being reduced to a minimum.

Built as extensions to the boundary walls of formal gardens, Victorian greenhouses and ancillary garden buildings provided strong inspiration for both the formal language and the physical significance of the project.

Budget constraints saw the use of modular building components to form two contrasting exterior and interior skins that line a structural steel frame. Exposed steelwork supports an intricate roof geometry, which cantilevers in two directions. The architect intended the design and details to be a celebration of the integrity of the stark multi-layered expansive building.

Architect’s opinion

The situation of the exposed building internally, as well as its relationship with the external masonry lining of the project, was very tightly controlled. Both are reinforced with a steel frame supported and cantilevered that support the complex roof geometry. This is located in height to meet a retaining brick wall. The volume is intentionally elevated to manage the transition from the existing apartment, while also being sunk into the garden to maximize the interior potential of the space and its connection to the garden beyond. The staircase, supporting spine wall, and interior seating are all a continuation of the raw material palette that sought to maximize the potential of the prefabricated building components throughout.
James Alder, Director, James Alder Architects

Customer’s point of view

We had an idea of ​​the extension and how the new kitchen might interact with the main building, but James used many different shapes of cardboard models to come up with a lot of ideas we hadn’t thought of. This allowed us to visualize 3D spaces much better than graphics.

Several material choices were imposed due to budget constraints but we really liked the idea of ​​concrete building materials like blocks and sills, reflecting some of the old, dilapidated exterior building materials. The use of exposed sills for standard structures such as stairs and open shelves became prominent features for us in the final design.

Construction began right at the start of the lockdown in March 2020, but James has been able to visit weekly throughout the year to help keep him on track in very challenging conditions. We decided to build the kitchen. Including making the cabinet doors ourselves to save money, and James helped us plan all the minute details. The new kitchen has changed the way we use the apartment as we now have two socializing rooms instead of just the living room previously and we like that sitting in the kitchen now feels like we’re sitting in the garden so the garden can be enjoyed all year round.

James’ design gives us more than we expected, with large windows, lighting and a sunken design that gives us a bright garden room during the day and a cozy basement dining area in the evening. Overall, we loved the process of working with James and couldn’t be happier with the final extension.
Kirsten Christensen Jeffries and Richard Manber, Clients

project’s data

Get started on the site March 2020
Completion date March 2021
Total indoor floor area 26 pm2
Total floor area (indoor + outdoor) 28m2
Contract form or purchase method traditional. RIBA Domestic Construction Contract 2018
construction cost £93,900
Construction cost per m2 £3,354
architecture James Alder Architects
client Spread
Structural Engineer Alex Mark (Mark & ​​Co.)
main contractor Lukasz Dziadkowiec (London Expert Builders)
Certified Building Inspector Ensure construction control
CAD software used Microstation

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