Britain’s best extension: curved double-glazed walls surround a courtyard that fills with rainwater in this award-winning renovation

A daring extension with aerial garden has just scooped this year’s top New London Architecture Don’t Move, Improve! Award.
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Philippa Stockley5 March 2018

To calculate the curvature for a super-slim plywood roof on their two-storey extension, Mike Tonkin and Anna Liu stood on ladders and suspended a roll of paper between them.

Their experiment back in 2005 demonstrated the natural line, showed where the roof should start and how low it would drop. It was one of many tests the architect couple carried out to ensure the performance and beauty of their curling, swirling, water- and sun-filled extra space, with its curved glass walls.

No wonder the project, called Sun Rain Room, has just been declared this year’s overall winner of New London Architecture’s prestigious Don’t Move, Improve! awards.

The Royal Institute of British Architects has already crowned it the UK’s best listed building extension. Set on the back of a five-storey Georgian townhouse in Finsbury, the whole amazing thing sits atop a new extension to the existing basement, creating a two-bedroom self-contained flat. Performance and beauty do indeed go hand in hand here.

Winners: Mike Tonkin and Anna Liu in their curvaceous creation with their dog, Be
David Butler

“We worked with three of the world’s best engineers,” says Tonkin. “And to test that the roof would support three tons, we hung water-filled plastic bags from hooks, set a laser to see if anything moved, and left it a few days.” He explains: “A litre of water weighs exactly one kilo.”

They designed the double-glazed walls around an ovoid courtyard that fills with rainwater at the touch of a button, making a shimmering, inch-deep pool reflecting house and sky. The couple, their teenage son Tainan, and their seven-year-old Silken Windhound, Be, love watching its constantly changing surface.

WORTH THE WAIT

But, having only got this daring project through planning at appeal in 2008, they still had to wait eight years to build it. It took that long to buy the rest of the house — three different dilapidated bedsits — like Monopoly, one by one. It was worth the wait.

Walkabout: curved, double-glazed wall
Edmund Sumner

Tonkin, 57, grew up in Georgian Bath. He and Liu, 52, from Taiwan, met in Hong Kong, where she worked for Arup. They came to London in 1997 and lived in a Marylebone flat that Tonkin owned. “We refused to move till we found something as beautiful.”

Two hundred and twenty viewings later, they saw a top-floor, two-bed in a five-storey terrace in the then run-down area near Sadler’s Wells. “The front of the house appeared to be falling off,” Tonkin says, “but it was only the paint.” As well as the tired flat, they also bought the building’s freehold.

This couple decided to be avant-garde at the back, but do very little to the house itself. Today, their practice’s distinctive designs, which mix natural forms with hi-tech geometry and structural innovation, have won many awards.

New va-va-voom: the madeover basement flat has its own little courtyard garden 
Edmund Sumner

The planners originally turned them down, essentially for removing the garden. But at appeal, the inspector called the project spirited and said the sedum and trees on the veranda roof created a new, aerial garden. Thanks to his vision, the plans passed. Now it is built, there is more greenery than before.

Not only does a blackbird rummage for worms on the roof, but a bold robin comes most days to admire himself in the wall of mirrored cupboards at the end of the courtyard.

To form the curvaceous roof around the yard, layers of plywood were cut on a CNC machine. The couple assembled it themselves, using waterproof glue and stapling it to a frame made by a boat builder. The veranda runs down one side and across the far end, uniting house and courtyard, and is in constant use.

TEXTBOOK RESTORATION

There were once five historic communal loos at the end of the yard, which made it bigger than other yards nearby. The couple raised the back wall a bit for the roof to swoop from, and replaced the lavatories with mirrored cupboards that hold recycling, a barbecue and garden kit.

When you cross the yard, you don’t notice the cracks between the slabs. This is where water swirls up from, giving the blissful illusion of a pond. Rainwater collects in a long, narrow tank that’s filled via a bespoke pipe and gutter, ready to pump.

Waterworld: at the touch of a button, rainwater creates a courtyard “mirror”
Edmund Sumner

The veranda roof itself is punctuated with stepped openings, which bring in light and add charm, especially glowing up through the sedum at night. Before the year-long build began in April 2016, the couple gently renovated the whole house. One by one, they reunited the flats, redid the plumbing and wiring, patched and limed the floors, restored cornices and repaired shutters — a textbook restoration.

The va-va-voomed basement flat now has a sexy new second bedroom with a curving back wall done in pine under the Sun Rain Room, and original tongue-and groove panelling and fireplace in its sitting room. The mix of old and new works well. It even has its own tiny courtyard.

This is a tale of two parts: conservative, feather-light restoration, enhanced by boldness and daring in the true spirit of the Georgians who built the house almost 200 years ago. Yet children who glimpse the courtyard, oblivious to its technical daring, just call it the house with a swimming pool — even though its depth would only take a tadpole.

  • Visit New London Architecture to see all of this year’s Don’t Move, Improve! winners and to find details of a free exhibition about the awards, running until April 20 at NLA in Store Street, WC1.

WHAT IT COST

First flat in 1998: £230,000

Remainder of house bought bit by bit: about £700,000

Money spent: £235,000 excluding all fees

Value of house now: £2.75 million (estimate)

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