An interior designer’s clever use of space and light gives a London flat a remarkable new space

The long, light-filled hallway of Katie McCrum’s north London flat leads to a sign marked “The Cabin”. Expecting to find a garden shed, I open the glazed door to discover an extension that feels more California than Camden. The walls are lined in pale Douglas fir, polished floors radiate heat from the underfloor heating. There is an airy bedroom, a shower and a compact kitchen, complete with flip-up dining table. Wide, sliding doors open on to the garden, adding to the air of seclusion.

McCrum, an interior designer with a background in property development, designed the cabin as a “flexible, multi-tasking extension” of her two-bedroom flat, set on the ground floor of a stucco-fronted house. It is a spacious guest bedroom for friends and family who can drift easily between the flat and cabin for drinks and meals. At other times, the Camden cabin earns a tidy keep as a short-stay rental for tourists who need a central bolthole.

“I’ve reached the point when I’m thinking of ways to future-proof my life. The cabin provides a sense of security,” says McCrum, who shares the flat with her partner, Leah Dunthorne – a strength and rehabilitation coach whose clients include Olympic athletes. “Looking ahead, we could get planning permission to turn the cabin into a separate flat one day. So we have options.”

 Light and airy: the ‘cabin’ bedroom, lined in Douglas fir and with sliding doors to the garden.

McCrum moved into the garden flat in 2003. Since then she’s eked out every last inch of the 680sq ft space, sneaking storage into empty corners, tucking a workstation into the steel kitchen and turning beams into bookshelves. Meanwhile, the marshalling yards and gas towers of nearby King’s Cross have been transformed into designer shops and flats and property prices have climbed. “We love our area, but we’d reached the point where we needed more space, but couldn’t afford to move around here. So we started thinking about the best ways to extend the flat.”

Then, six years ago, McCrum had a phone call. It was a developer “casually” announcing his plans to build a four-storey block of flats on the vacant plot next to her building. Months of dirt, drilling and the dawn-to-dusk rumble of lorries lay in store. But instead of accepting the usual, nominal compensation, the clear-eyed McCrum sensed an opportunity.

“The first thing I did was to call every expert I know,” she says. Her clients include the painter Raqib Shaw, as well as developers. A right-of-light specialist who advised on the Gherkin, a surveyor and an urban planner helped to broker a deal which included sensible compensation. More strategically, McCrum negotiated with the developer to build a structural wall, perpendicular to the flat, as “an anchor” for the extension.

Space saver: the ‘office’/ kitchen/shower room seen from the bedroom.

“Without all the advice I garnered I could have ended up with nominal compensation and no wall. At least at the end of two years of disruption I had something to look forward to,” she says.

“I spent a long time figuring out how to connect the extension in light, fluid ways so it could be a separate space, but also part of the flat,” says McCrum, who worked with George Bradley of BVDS Architects to design the 230sq ft addition. Clever devices include the Ikea screen that divided the garden in two. In summer, the opaque glazed doors can be left ajar, breezy linen curtains pulled across for privacy, skylights open for ventilation. McCrum’s “patient glazier” also made the new, bi-folding window which opens from the kitchen in the flat, on to the hallway: “We can chat to friends as they go into the cabin. It’s made the corridor another sociable space.”

McCrum sees the cabin as a distillation of lessons learnt working with private clients and cost-saving developers. “You have to prioritise, spending money on what matters.” The interior was inspired by a holiday spent in a cabin in Joshua Tree National Park in California.

Joined up: the new kitchen, leading to the main flat’s hallway.

“I wanted it to be the perfect place to unplug from the city. It can be a bright sunroom, at night you can gaze up at the stars from the bed,” she muses. For the walls and mini desk, she used Danish wood flooring. The floors are micro cement, brass taps gleam in the shower-room, and the kitchen is Ikea, souped up with bespoke doors and handles.

The cabin is a shared project for McCrum and Dunthorne. “Leah and I are a top team. If I had another job, it would probably be a hotel inspector,” she laughs. They wrote the cabin guidebook, deliberated over the bedlinen, and together stock the fridge with snacks and locally-brewed beer. A guest book filled with enthusiastic scrawls has earned them “super-host” status on Airbnb. “We like being able to share the cabin with others but to close the front door and have the place to ourselves when we feel like it. It’s all about flexibility.”

Katie McCrum’s top tips on designing a flexible extension

• Start by researching other extensions in your area by looking in the planning section of your local council’s website.

•Find an architect who is experienced in dealing with your local council and understands your budget and ideas.

•Consider natural light. We used skylights in the hallway and cabin, and reeded glass in the doors to give a bigger, brighter feel.

•Maximise ceiling and door heights. It is another way of enhancing the space while creating a connection with the outside.

•For compact spaces use the same flooring throughout to add cohesiveness.

•Small details, such as brass handles and contrasting paints, add interest. We used an Ikea kitchen with bespoke doors.

•Factor in a contingency budget. There will always be things that you haven’t budgeted for, or decide you can’t live without.