Civic’s glazed garden room uses the sun to heat and trees to shade

Can you describe the project?

The morning sun path and tree shade from several neighbours’ back gardens inspired this glassy kitchen/dining room extension to our family house.

An original, single-storey rear extension and a small glass porch were demolished to make way for this scheme. The footprint of both these small structures has been subsumed into a new open-plan living space, giving significant amounts of daylight and immersive views of the garden.

The new space was designed as a single garden room for the house, oriented (predominantly) east to allow productive winter sun to passively heat the home when the leaves are off the trees. The heavily neglected existing glass porch and lean-to outrigger building – probably the old scullery – gave simple inspiration to setting the scale and dimensions of the proposals: its height and the extension’s footprint.

What was the brief?

I wanted to create a new kitchen and dining room space for my own family, on the ground floor of a three-storey, semi-detached, Edwardian house in Honor Oak, south-east London. We wanted to extend and open up the existing ground floor living area to a sunny, south-east-facing garden courtyard and a raised planted garden beyond. The result was a pared-back, single-storey, rear and side addition that seems to provide a feeling of space while only increasing the original footprint by 13m². This modest increase in the footprint area was driven by cost, yes, but also by limited need. Once the original building’s internal and external walls had been excised, the plan became more economical and the space available was easily sufficient.

How was the planning process?

Our decision to continue the aluminium sliding doors down the side of the house to face into the sunshine meant we had to work to win over the planners and building control. All the neighbouring houses have their back doors opening onto the garden. And this one does that too but it turns sideways as well, so the majority of the glazing faces east.

The house is in a conservation area where the fronts of buildings remain mostly as originally built but the rears reflect a wider range of approaches to domestic development. Back add-ons, original outriggers, contemporary kitchen extensions all make one overall ‘project’. Painted, rendered and self-finished brick walls come together to display a heterogeneous character. In some places, small, flat roofs are used as garden-facing terraces. Velux roof windows pepper roof planes at all levels from ground floor to top floor. Against this backdrop, we wanted to create something sharp and quite formal, but low-slung and settled into the ‘hollow’ where the building meets the garden.

Explain the external treatment of the project

Glazed elevations are topped by a low-pitched roof which stretches out in elongated, horizontal proportions. At 15 degrees, the roof is unusually shallow-pitched for natural slate, made possible here by oversizing the head and side-laps between slates.  

Seen from the garden, the resulting gable can appear to float, and quite literally does float at the corner where engineer Price & Myers has designed out columns completely. This allows easy access to and from the new sitting area outside.

Every window slides freely in both directions making for a flexible enclosure. Among other things, this makes it easy to carry indoor furniture outside, for example at family events, or other social occasions. This has the added benefit of making it easy to change the cross-ventilation path through the space on warmer days, and to take advantage of the sun when it comes out on cooler days.

How have you designed the interior?

The interior is a simple diagram that is open to the garden and solid against the house. On one side, sliding aluminium windows are both transparent and reflective, meaning at some times of day reflections of garden foliage can surround you like wallpaper.

On the other side, kitchen cupboard fronts are dark-coloured and cossetting. Together with the solid ceiling in this half of the room, they create a cave-like setting for more domestic activities like cooking.

The new ceiling level, which is drawn from the original house, sets the height for all the sliding window walls. This datum separates the floating roof and supporting plinth. ‘Hit-and-miss’ fence panels along the boundary enable the neighbour’s side return brickwork to ghost the real, hard edge to the space.

What was your approach to sustainability?

Orienting the scheme to face into the morning sunshine has reduced whole-building CO₂ emissions by reducing the winter heating load. This orientation allows the sun to passively heat the home.

Summer overheating is largely blocked by nearby mature, deciduous trees. The building shades itself in the afternoons. An exposed concrete floor, generous whole-space cross ventilation and whole-house stack effect ventilation (via the central staircase) mean the extension is passively cooled with no mechanical backup.

More than 25 per cent of the extension’s total floor area is covered by glazing so calculations had to show atypical compliance with the Building Regulations (Part L). They showed the whole house was warmer with the extension than without. This is because the extension – even with all the glass – dramatically out-performed the uninsulated, solid wall, single-glazed, original construction it replaced, especially once the passive benefits of solar gain had been factored in.

What was the main challenge? 

This is perhaps a simple-looking building but it wasn’t simple to build. Self-finished materials such as the Douglas fir timber frame and the polished concrete floor went in out of sequence and subsequently had to be protected from the weather and from the building process. Traditional construction normally sequences trades from the ground up so this project was effectively sequenced upside-down: roof first, then the walls, then the floor. Consequently, reproducing construction details accurately was something the construction team worked hard to achieve – a daily conversation between the builders and me as the architect.

What is your favourite detail in the project? 

Strips of American cherry finished in Danish oil are used as an interior wall covering at the back corner of the space, concealing secret doors to a laundry, utility room and WC under the stairs. This curving, stripy fascia, while a homage to Asplund’s sinuous courtroom table fronts in Gothenburg, gives good relief to this part of the proposals at an important junction between the extension and the original building. It was also an area where the main contractor, Swallow’s Tail Construction, really excelled.

Are there lessons from this project that might be applied elsewhere?

The first idea came from an observation that we were sitting in a cold house in winter – solid brick walls, no insulation, single glazing – and that there was an oasis of useful winter sun outside not being used; just waiting to be let in. Next, we realised several large, mature trees across neighbours’ back gardens would actually shade the extension from the most harmful summer sun. So this project became about passive design: passive warming in winter; passive ‘cooling’ in summer; and all CO₂ emission-free. This approach to passive environmental design remains a prevalent interest in many of the projects in the office, along with our evolving interest in timber structures.

Dan Jones is co-founder of Civic

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Key data: 
Total contract cost Undisclosed
Area of extension 45m²