Our home: converting gloomy basement flats

Gloomy, badly lit rooms, a slight subterranean dampness and the sight of strangers' feet glimpsed on the pavement outside the barred windows: everyone knows the unappealing cliché of the urban basement flat.

And indeed Barbara and Alistair Webster were far from overwhelmed when they first viewed their two-bedroom, split-level property. "The entrance was like the black hole of Calcutta, the sitting room was dark, the kitchen was horrible, and though it still had its nice sash windows there were very cheap finishes - and it was cold because there were hardly any radiators," said Barbara. Three years on, and a £250,000 makeover later, the flat is an inspriation, a model of how to reinvent basement living.

The couple, both 58, bought the flat in 2008. They are based in London and Manchester, and the fact that the property is in Islington and convenient for Alistair's work as a QC was a big selling point. It also had two good-size bedrooms plus a garden for their three cats which commute between homes with them.

They paid £595,000 for the property and then quickly turned to their daughter Lizzie for advice on how to turn this sad little property into a perfect London base. Lizzie is the co-founder of Fraher Architects (fra-her.com) and was faced with a daunting wish list from her parents/clients.

"We knew immediately that we needed to open up the dark sitting room. We also wanted a good kitchen with lots of work surfaces and, as we like to eat with our family, we needed a dining room with space for a big table," said Barbara. "The front of the house was dark and miserable when you opened the door and there was no storage, and we needed somewhere for Alistair to work."

All of these demands meant that extending the house was inevitable, and Lizzie and her partner, Joseph Fraher, drew up three sets of plans. Her parents' favourite was also the most radical. "At my age you can get quite conservative but Lizzie and Joe made us think outside the box," said Barbara.

Though the flat is within a Grade II-listed Georgian terrace, Islington council was surprisingly open to the contemporary design and they won planning consent at their first attempt in August 2009. Work on the build began the following March, and the couple were able to move in last November.

The first challenge was to deal with the darkened entrance hall. The original steps from the street were replaced and the front wall slightly pushed outward to create a larger lobby lit with a skylight.

At the same time an external vault that extends beneath the pavement was opened out for storage. The downstairs rooms were knocked through so the dark sitting room benefited from direct light from the south-facing garden, and a wall of bespoke cupboards, built of birch ply with a white lye finish, resolved at least some of the storage issues. Some shelves have been left open for books and photographs and two cupboards hide a media unit and a work station for Barbara, who is a jewellery designer (barbarawebsterjewellery.co.uk).

The kitchen is also bespoke, with maple veneer doors and floating cupboards that, by optical illusion, make the long, skinny space seem wider. The work surface is a thick chunk of sandy coloured concrete, polished smooth and shiny on top but with a "bug splatter" effect on the sides to give texture and interest. The floors are a grey concrete/resin mix. "I really enjoyed all these new surfaces," said Barbara. "It would have been so easy to go for the usual granite."

The house has been extended at the back, giving room for an extendable table large enough to seat the whole family, and a glazed office "pod" with built-in desk and shelves. Two fabulous, sinuous plastic outdoor lights with long leads have been hooked from the ceiling to give overhead light.

And that ceiling is no average ceiling. It is, to give it its technical name, a split butterfly roof, which tilts at two different pitches. It is clad in a ribbed birch plywood, backed by strips of black MDF to emphasise the shadows the grooved timber creates; outside the same material has been used to clad the rear of the property.

Because the site slopes, in the original design the kitchen looked straight out on to a concrete retaining wall. In order to improve this prosaic vista some 25 skiploads of earth were removed, painstakingly, to lower the level of the garden. A new French window now gives direct access to a paved courtyard area. Steps then lead upwards to a second garden area with raised concrete planters and a subtle water feature.

The attention to detail in this project has been tremendous. All the doors slide into recessed pockets in the wall to save space and create cleaner lines. Underfloor heating did away with the radiators and maximised wall space, and with no skirting boards the walls looked seamless. A rainwater harvesting system and automatic irrigation means that the garden effectively keeps itself watered when the couple are away.

"It was designed with so much inbuilt storage that the only things my parents needed to buy were a sofa, a dining table and beds," said Lizzie.

Upstairs the surviving original features, including coving and sash windows, were preserved, and new Douglas fir floorboards - identical to the long, light boards in the Saatchi Gallery - were installed. And, charmingly, the extension has a green roof sewn with sedum and wildflowers. So the couple have been able to enjoy a profusion of English flowers all summer and are now looking forward to the burnished reds and greens of the sedum during the autumn.

This kind of high-spec project does not come cheap. The £250,000 budget excluded fees, though the Websters did get VAT relief because the building is listed. The end result, however, is stunning enough to have attracted several hundred visitors during the recent Open House weekend which celebrates the best in London architecture each year.

Little black book:

* For concrete work surfaces contact Low Info (lowinfo.com).
* The hanging Uto lamps in the dining area are from Modular Lighting (modular - lighting.co.uk).
* The extendable dining table was sourced from Innerform Contemporary Interiors (innerform.com).
* The stairs and bedrooms have timber floors by Dinesen Wood Floors (dinesen .com).
* For wildflower and sedum roofs contact Lindum Green Roofs (lindumgreenroofs.co.uk).

Pictures by David Butler