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The industrial building conversion has to be the single biggest surprise source of new homes to emerge over the past 20 years.

Deserted old brick warehouses and redundant factories, the detritus of the industrial age, were unloved and unwanted — until that light bulb moment when we walked inside and fell in love with the high ceilings, iron fittings, chains and pulleys, and the light from huge metal windows.

The industrial warehouse was a big, bright galaxy of opportunity bequeathed during the 18th and 19th centuries, when they were built to store sugar, spices, rum and all manner of exotic imports. Conran saw their worth in Docklands, where a few other brave hearts bought shell spaces to convert themselves.

Mr Warehouse Conversion himself, Harry Handelsman, seized his first old industrial unit in Clerkenwell for a song. No one wanted it — it was easy to turn your back on such cold, dirty buildings with their smashed windows and heaps of bird droppings.

Now, though, we all lust after a warehouse home. They sell for millions. So why were we once so blind? The green gang, at least, should have realised that converting warehouses into homes is the biggest recycling project in the history of building development.

Two to one: Kate Koumi and husband Jamie Lane created two warehouse flats in their former recording studios with the aim of turning them into their own single home one day (Juliet Murphy)

In Fulham, Kate Koumi saw the light. She has turned a blocky brick industrial unit, bought to use as a sound recording studio, into two flexible warehouse apartments, designed to convert to one house when required.

For almost 30 years, Koumi ran recording studios: first for Nick Mason of Pink Floyd, then independently from 1995 in a two-storey brick office building near Wandsworth Bridge that she had converted into studios. During her 18 years in business there, she worked with everyone from Adele to Kylie to Westlife.

“The insulation was so good — with brick walls a foot thick, the ceilings industrial concrete and steel — that you could record a violin solo while juggernauts roared past outside.” But Koumi, 59, and her husband, Jamie Lane, 65, a former session drummer with the likes of Tina Turner and 10cc, now a musician, didn’t want to be 70 and still producing music. “It’s a young person’s game,” says Koumi.

So in 2013, the pair decided to convert the studios into their house. That year, a change in the law gave a three-year window to convert commercial premises to residential under permitted development rights. Plans had to go before the council, but as long as your designs met certain stipulations, they would be passed. “We’d been thinking about doing it, and this change in planning law seemed like a sign,” says Koumi. The couple got stuck in straight away.

Greek Cypriot Koumi found the SW6 building in 1995 by scouring London, driving around while pregnant with their daughter Lucia, now 21. Koumi spotted the broken-down old offices in a whole road of “crappy buildings”.

Industrial look: exposed brick, floor-to-ceiling windows, high ceilings and painted concrete floors firmly establish the warehouse feel (Juliet Murphy)

When it came to planning their house, she did the drawings herself, getting an engineer in to do some structural drawings. They planned to gut the two floors and sandblast the brick walls, leaving them exposed, and paint the concrete floors.

With the fabulous, very high ceilings they decided to retain the industrial look with surface-mounted metal conduit, and air-conditioning in great industrial pipes round the top.

Then out of the blue, Lucia said she was upset about giving up their family house in Battersea in exchange for a converted warehouse. “So we made a change,” says Koumi. “We decided to initially convert the warehouse into two flats and rent them out, then when she is settled down somewhere we will convert it back into a home and move ourselves in. So we designed it with that idea in mind.”

The council then put a spanner in the works. A laundry once stood on the site and there was a question of toxic chemicals in underground tanks. Koumi and Lane had to monitor the situation for a year. The chemicals didn’t materialise, but it added £15,000 to their costs.

Then the Environment Agency stepped in. The building is near the river and there’s a low risk of flooding, so the pair were instructed to raise the concrete floors about eight inches, boosting costs again. Once these hoops were jumped through, their builder, Ross, a former guitarist, could start work.

Aiming for a fast build, the studios closed in September last year and the rip-out began two months later, with the project finishing in summer this year. Demolishing the 1ft-thick interior walls created mountains of rubble. Koumi was in charge of design, and Lane was researcher, “searching online, night and day”, he says.

Koumi adds: “Once we decided to rent out we knew everything had to be idiot-proof — good quality and bulletproof.” The floor paint is “car-showroom durable” in a sensible mid-grey. Once the walls had been sandblasted, Lane recalls crawling all over them to pull out hundreds of rawl-plugs and fill the holes.

They ripped out the staircase that cut straight across the floor-to-ceiling windows at the front and put in a central stair, encased in soundproof blockwork. They budgeted £100,000 per flat, to build and furnish.

Hitting the sales months ahead, Koumi bagged bargains including industrial-style lamps from Habitat and industrial-looking radiators off a website. She bought robust leather sofas, and white paint to refresh between lets. A black kitchen was chosen for a sleek look. The sink is welded seamlessly into the steel worktop. It’s a good touch that raises the game.

The two bedrooms and two bathrooms to one side are practical. The bricks add warmth, and the young tenants — one a singer — love it.

WHAT IT COST

Two-storey warehouse building in 1995: £200,000

Total spend on converting and furnishing both flats, each around 900sq ft: £210,000

Value now: flats valued at £899,000 and 980,000.

KATE’S TOP TIPS

Use trusted ordinary paint brands that you can refresh between tenancies — and choose colours that are unlikely to be discontinued.

Buy top-end products such as boilers, switches, and good-quality kitchen appliances. Give tenants drain unblocker, dishwasher cleaners and so on, to use each month.

Put in power showers and heated towel rails, not baths, and always buy leather sofas and wood-topped furniture that can be sanded if marked.

Pocket doors save space and look good but designer furniture blows the budget — so forget it. Set a budget and stick to it.

GET THE LOOK

Design by Kate Koumi: email kate@britanniarowstudios.co.uk

Builder: Ross Malone at Orchestrate Ltd

Industrial floor paint: from Resincoat

Industrial-look pendant lights: Habitat

Slatted loft-style Venetian blinds: London Blinds 4 U

Black gloss kitchen units: DIY Kitchens

Stainless steel worktop: from Stainless Steel Worktops

Black Fridgemaster fridge: from AO

Leather sofa: DFS

Leather armchair: Ikea

Revive radiators: from Mr Central Heating

Wooden-topped side tables: from My Furniture

White paint: from B&Q

Sliding track for master en suite and all door furniture: SDS

Porcelain bathroom tiles: from B&Q

White goods and bathroom cabinets: from Victorian Plumbing