When their first builder disappeared after demolishing a great deal of the little property they’d bought as their first project and home-to-be in Barnes, and couldn’t be reached by phone, Jennifer Hunt, 26, a marketing manager for Conran, and her fiancé Lee Mainwaring, 33, an architect, gritted their teeth.

Luckily, another member of the building team set up a new company to honour outstanding contracts. Even so the couple, who were on a very tight budget, lost some money, so eventually moved into what was basically a shell, with two little bathrooms, and then set about doing the final work themselves.

“After a long day at work you don’t feel like doing DIY, and every weekend too,” says Lee, who remembers as particularly grim all the endless painting of the white walls. “However, we could easily design our own kitchen,” says Jen, “which we designed round all our things.”

“Well,” Lee chips in, “the last thing we wanted was an Ikea sideboard because we’d miscalculated the storage.”

In fact, their storage calculation is particularly good, leaving the downstairs as one clean 30ft x 15ft open-plan space, with folded oak stairs dancing up one side, and a luminous polished concrete floor.

Practically all our own work: Jennifer Hunt, her architect fiancé Lee Mainwaring and their smart folded oak stairway (David Butler)

The kitchen area is at one end. Its white Corian-topped central island houses cupboards and the dishwasher, and sits in front of floor-to-ceiling cupboards along the back wall that hold everything, all nicely calculated — down to the slot for the ironing board — a simple thing that makes a difference.

There is no kettle because the smart coffee maker dispenses boiling water. And all the pipes for the underfloor heating, and the boiler, too, are tucked away here.

They haven’t wasted an inch of space. The house is just shy of 1,000sq ft but looks larger because of meticulous planning. Their folded Brompton bikes live in the back of the mirrored hall cupboard; the upstairs bathroom has two large mirrored cupboards sunk flush-fronted into an extra-deep stud wall so you don’t realise they’re there; the beds in both double bedrooms lift up.

The crawl-space loft runs the length of the home, and — best of all — what looks like a shallow chimney breast holding the big wall-mounted TV opens outwards around the screen to reveal shelves behind, while neatly covering one of the huge steels that support the house.

Now, sitting in this two-storey modern, light and white home with sunlight blazing from three sides, looking out to the bright little courtyard with its silver birch turning autumnal, all the angst is forgotten. Taking the leap, taking a risk, investing all their money, has left Jennifer and Lee in possession of a perfect first home.

“We’re quite fussy, and we both like minimal,” Jen says. Even though Lee is the architect, Jennifer also trained as an architect. She met Lee in 2012, before he set up his own practice with two others. At first they lived in the little flat he had bought in Kingston, where he was studying. “But we thought, interest rates are so low, why not push ourselves?” Lee says.

They loved Barnes, with the river, and long walks, and great pubs. But their £600,000 budget wouldn’t stretch to the million-pound terrace houses in what’s sometimes called Little Chelsea.

Then, online, they spotted an unusual property — the back half of a house, mainly the double-height dog-leg extension with its side return and small garden. It was run-down and subdivided, and being used as an office. A conservatory was tacked all round, covering the side return and half the back garden.

A rare find: the couple spotted the unusual property, which was being used as an office, online (David Butler)

“We walked in, and realised that if we could extend the building out to where the conservatory was, we’d get a big ground floor,” Lee says. They went to the owner and told him what their absolute top price was. “He accepted, and we shook hands.”

Very shrewdly, before completion, Lee got in a structural engineer and a quantity surveyor and worked out what could be done. It turned out that the original plans said the house couldn’t be extended, but said nothing about alterations.

Because of this, following discussions with the planners, Lee learned that if he stuck scrupulously to the existing boundary of the rickety conservatory, he would be able to move the walls out, and also insert some stylish windows into the side wall of the building. Even better he could do it all within permitted development rights.

That was a piece of good luck. He submitted plans, which you still have to do with permitted development, achieved a certificate of lawful development, and building began in October 2014, finishing in May last year.

One of the contractors Lee got in was the polished concrete specialist. “Nine guys came in a truck at 7.30am, poured 100mm of concrete, then hung around waiting for it to set just enough.

“Then they all piled in, smoothing and polishing it, working their way from the inside out, working really fast, and left at 9.30pm. It had to cure for a week after that, and was one of the most expensive things — but we love it.”

Rightly so: it is such attention to detail that makes this simple but beautifully considered space. “Children love it here,” Jen says. “They especially love the polished concrete. They can whizz cars on it, and bash it, and it doesn’t mark.”

WHAT IT COST

Half a house plus conservatory in 2014: £595,000

Money spent (including furniture, but no professional fees, and much work done by the couple: £130,000

Value now (estimate): £1.35 million

GET THE LOOK

Architect: Lee Mainwaring, partner at architectureinitiative.com

Pendant lamp on stair, other fittings: designed by Lee and Jennifer Hunt

Concrete floor: laid by Steyson at steysonconcretefloors.co.uk

Slimline aluminium windows and bi-fold doors: by Reynaers at reynaers.co.uk

Kitchen units: by unitsonline.com

Extractor: by Baumatic at baumatic.co.uk

Coffee-maker: by Siemens at siemens.co.uk

Downlighters, pendant, and yard lamps: by Delta at deltalight.com

Mirrored wardrobes: from ikea at ikea.com

Inset bathroom cupboards: by Vitra at vitraglobal.com

Wall-hung composite stone sink: by admbathroomdesign.com

External render: by Weber at netweber.co.uk

External paint: Dusky Parakeet from Valspar at valsparpaint.com

Warm white paint throughout: by Dulux at dulux.co.uk

Plants supplied by Provender Nurseries in Kent: provendernurseries.co.uk