We thought outside the box to extend our homes

When Kirsty and Andrew Cocker were planning to extend and refurbish their family home, there was one thing they definitely didn’t want: anything normal.
“I think that everyone else on our street has built a square box extension — like a car showroom,” Kirsty explains. “That was the antithesis of what I wanted.”
What Kirsty did want was an extension with curves and sharp points, not to mention a tree growing out of the floor. And although the project was partly designed to make a visual statement, there are also practical reasons to think outside the box.
Asymmetrical designs like Kirsty’s can help owners to maximise space (while sticking within planning rules) and create lighter, airier new rooms, more so than a straightforward cuboid stuck to the back of a house.
Yes, they are more expensive to build. But homeowners trying to create a long-term place to live consider it money well spent.
Given free rein, Simon Gill, principal of Simon Gill Architects, designed Kirsty and Simon’s rear extension with one straight wall, one curved wall and a triangle-shaped promontory reaching into the back garden.
Bringing the design to life wasn’t easy. Getting planning consent for the project took three attempts, and Kirsty acknowledges that the build itself was more difficult and more expensive as a result of her desire for an unconventional layout.
“We wanted a modern house in an old shell,” she says. “We wanted to create some really interesting spaces and to have something nobody else has. We wanted it to be original and unique, and there is a real sense of drama.”
Kirsty, 46, an interior designer and founder of Ixia London, and Andrew, 49, who works in marketing, bought their house in Turnham Green, west London, in 2019. The semi-detached house was derelict when they took it on. They wanted to keep its Victorian façade and build a modern house behind it, with six bedrooms and a new basement level for them and their three children.
The work took 15 months and was completed in 2023.
Today, visitors are greeted with a view straight from the front door through to the back of the house, where the curved section of the extension has an olive tree growing indoors. Its roots are contained in an earth-filled metal box below the floor, and it is lit by a skylight directly above. “I wanted to bring the outside in,” Kirsty says.
Beyond its visual appeal, the triangle of windows in the dining area means that the west-facing house gets natural light all day long. “It was designed [like that] because of the orientation of the house,” Gill says. “Light pours into the side of the dining room in the middle of the day. If it was just a box that wouldn’t happen.”
The bespoke nature of the extension added about two to three weeks to the build time, Gill estimates, and about £20,000 to the project budget. This was mainly because the irregular wall required more building materials than a straight edge would have.
But it also contributes to a stylish home that Kirsty rents out regularly for photoshoots, which in time will offset that extra cost.
Amy Livingstone and Niko Fischer bought their semi-detached house in Whitstable, Kent, six years ago as a family home for them and their two children, aged eight and six.
The house is in a great location, close to the sea, but it had some serious flaws, notably the low-ceilinged, pokey galley kitchen.
What the couple wanted was a bigger, more welcoming family space, so they hired Damian Howkins, founder of Damian Howkins Architects, to help.
“The easiest thing would have been to chuck a box on the house,” says Niko, 28, who works in healthcare tech. “But we didn’t want anything vanilla.”
Despite the tight space he was working with, Howkins came up with a saw-toothed design, its shape dictated by the wall heights of the adjacent houses and the bathroom windows on the first floor above.
“The ceiling is up to three metres high in places,” Niko says. “It never gets boring, and because there are two skylights on the roof it gets an amazing amount of light.”
The work took six months to carry out in 2022 and cost just over £120,000 including VAT. This included the cost of draining and filling a 4m-deep well that they discovered behind the house.
Before the project, Niko and Amy, 41, a teacher, did get some quotes for a basic box extension. They were quoted from £70,000 to £95,000.
“Yes, we could have paid less,” Niko admits. “However, in my opinion you get what you pay for — we really were happy with the end result. We didn’t want to do a quick job so we could flip the house and move on. We will be staying here for at least five years so it has been worthwhile.”
For Caroline and Alan Burns, moving away from the conventional boxy extension trope was all about maximising space and light in their kitchen extension. This has been achieved by creating a dramatic bow tie-shaped room angled to hide the ugly neighbouring wall and trap as much sunlight as possible.
The couple, both 50, bought their semi-detached Victorian family house in Crouch End, north London, in 2021 — they were already living locally with their three children, aged 11, 14 and 16, but wanted more space.
The house needed a full refurbishment, including an upgrade of the rear kitchen extension built in the 1980s. “It went the width of the house, and it had a little door and a window which looked out at the side of the house next door,” says Caroline, a human resources director.
While kicking around possibilities with Mulroy Architects, she and Alan, chief finance officer (CFO) of an online company, were taken with the firm’s idea of a bow tie-shaped extension. It would not only hide most of next door’s two-storey side wall, but give them a 4m-tall double-height space on one side of the extension.
The roof pitches downwards, accommodating the first-floor windows, before rising again to meet the boundary with the home on the other side.
Skylights bring light in from above, and the extension is angled at 45 degrees to the back wall of the house, to trap yet more light.
“We aren’t now looking out at a big brown wall,” Caroline says. “You can only see garden and sky, and we get the sun in the afternoon.”
The design was granted planning permission without any hitches and work began in October 2021.
By March 2023 the house had been remodelled and extended, adding space for another bedroom, extras like a cinema room, gym and office, plus the large open-plan kitchen living room, which opens out on to the garden.
“The extension is literally the heart of the house, it is used constantly,” says Caroline, who can now comfortably entertain a couple of dozen guests in the space.
This was a no-expense-spared kind of project, aimed at creating a perfect, long-term family home, and it cost £430 a sq ft. Part of this money went on lowering the floor in the kitchen to make it as airy as possible, and cladding the extension in a mix of pale brickwork and Siberian larch, as well as on digging out a basement and moving the main staircase.
“Was it worth the money? Absolutely,” Caroline says. “We were very fortunate that we were able to do what we wanted to the house, but Alan is a very good CFO and was all over the finances. Every decision was very considered.”