Adrian James completes cantilevered concrete gazebo


The brief called for a sculptural covered terrace in the garden of an 1887 house in north Oxford formed out of a single material and referencing Brutalist architecture, particularly the 1963 Sheats-Goldstein residence in California – with the aim of totally contrasting to the existing.

Exploiting its structural potential, the concrete canopy is cantilevered out of the existing building on four slender columns away from its corners, arranged as two interlocking proscenia.

A triangular geometry gives the canopy a sharpness while its soffit has been coffered, reducing its mass and weight and minimising the amount of concrete used. Small circular pavement lights sit within the soffit, bringing light onto the polished concrete terrace.

The use of concrete has been offset through the financing of new woodland planting in Yorkshire, offsetting 50 tonnes of carbon in total.

Adrian James Architects worked closely with specialist contractors Conform to use specific timber for the concrete’s formwork with 10 times more uses than traditional formwork plywood.

Architect’s view

The first question was, inevitably, whether it had to be concrete.

I used to be an ardent advocate for the material. Twelve years ago my practice designed a house whose structure and interior were entirely precast concrete. Slim concrete panels were assembled like a pack of cards in less than a week; the interior was self-finished, extremely durable and a thing of austere Ando-esque beauty. It felt like the off-site future but it also felt timeless; to go through the front door was to immerse in a sea of tranquility. The house was shortlisted for the Stephen Lawrence Prize and it won the annual Concrete Society award for the best concrete building in the UK.

But times have changed; there is an elephant in the concrete room and it has a very large carbon footprint. We simply must look at alternatives to concrete wherever we can.

I do not agree, however, with those who advocate that concrete must go. It is the most versatile and useful building material on earth. It is the opposite of plasterboard which makes every building a cheap stage set; it is hard reality. And actually it need not be such a carbon bogeyman. Concrete is top of the form for thermal mass. Concrete cuts the need for cladding or finishing materials and coats. Concrete is nine-tenths inert rock and sand, stuff which can be sourced locally and lasts forever with no carbon impact.

Concrete is basically glued gravel, and it is only the glue that is the problem: the cement. The industry is acutely aware of this issue and is urgently researching how to decarbonise cement and/or find alternative glues. It would be nice to think that in ten years time the cement conundrum will be solved and concrete can claim to be the world’s most useful building material with a clear conscience.

It’s not there yet, but nonetheless concrete has some intrinsic qualities which mean it should not be ruled out as an option. It is just that if it is selected with good reason then every effort should be made a) to reduce its carbon footprint and b) to exploit its unique characteristics by designing a building which can only be constructed using this extraordinary material and which uses it for both structure and finish.

So these are the two objectives we set ourselves here. We designed a structure which could only ever be concrete with its combined strength, plasticity and water resistance. And we looked at four routes to reducing the carbon footprint.

Adrian James, director, Adrian James Architects

 

Client’s view

I loved the John Lautner Sheats-Goldstein house in LA, especially the concrete roof.

We wanted inside-out kitchen space for our 1887 Victorian house which wouldn’t detract from our lovely house and be totally modern and brutal like an art space and not try to copy the Victorian house. From this whim AJA managed to come up with this design and got it through planning, and then CentreSpace did the structural drawings. We appreciated that what we were doing would have a relatively large carbon footprint so AJA worked out how much carbon we needed to offset and we funded ‘Make it Wild’ to plant trees in Dacre Lane Reserve North Yorkshire (50 tonnes of CO2 offset).

Concrete works were done by Conform contractors, who do specialist in-situ concrete for Oxford colleges and others. Adrian James Architects did all the technical drawings, liaised with the structural engineers and other contractors and even designed the stainless steel gutter which looks like an elongated pull handle!

Private client

 

Project data

Start on site March 2023
Completion October 2023
Gross (internal + external) floor area 60m²
Form of contract JCT Minor Works
Construction cost Undisclosed
Architect Adrian James Architects
Client Private
Structural engineer CentreSpace Design
Lighting designer Delta Light
Principal designer Adrian James Architects
Approved building inspector Oxford City Council
Main contractor Conform Contractors
CAD software used Vectorworks

Environmental performance data

Percentage of floor area with daylight factor >2% Not applicable
Percentage of floor area with daylight factor >5% Not applicable
On-site energy generation 0
Annual mains water consumption Not applicable
Airtightness at 50Pa Not applicable
Heating and hot water load Not applicable
Overall area-weighted U-value Not applicable
Design life 100 years
Embodied/whole-life carbon
450 kgCO2eq/m2
Annual CO2 emissions 0.06 kgCO2eq/m2



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