The nurserymen who brought the outsized planters to Martin and Jan Disler’s house in Marylebone, central London, last year were none too delighted when they found they had to cart them up to a roof garden five floors up. Not only has the building been converted back from a warren of bedsits to a single house covering 5,000sq ft, but an extra floor has been added at the top. There is now also a four-storey extension, running at a curved right angle to the house.

As well as the garden at the top of their house, the Dislers have taken maximum advantage of the new levels and rooftops. So, instead of having only a dark well at the back of the building, kept in the shade by the walls that surround it, as in many city houses that have been extended, they have a choice of four outdoor spaces, totalling more than 750sq ft.

The family moved to Marylebone from the north London suburbs last year. “We’ve become a pedestrianised family,” says Martin Disler. His two daughters, Talya, 13, and Romy, 14, now walk to school, just round the corner and their parents can walk to their office near Oxford Street, where they work in the clothing industry. “It has given us a whole new outlook on London,” he says.

Whereas none of them misses the journey of more than an hour to get into central London, they did feel sorry to leave behind their 150ft-long garden and the outdoor living it allowed. So when Disler, who trained as an architect himself, enlisted the help of KSR Architects to convert the house and build the extension, he asked for a terrace on its roof.

At basement level at the back of the house is a lightwell, with the ground covered in large, decorative pebbles and a single, stylish phormium in a pot. At ground level, on the roof of one of the basement rooms and with access from the extension to its side, is a small decked terrace. The surrounding walls are clad in a mixture of weatherproof American Douglas-fir strips and an unpainted pale golden render, which has been mixed with white rather than grey sand to reflect the sun more effectively.

The plants here are evergreens such as fatsias, which thrive in the relatively low levels of light, and an acer in a large pot.

In contrast, sitting on top of the curved extension is a decked roof terrace, which faces west. Olive trees thrive here in the full sun. The roof is strong enough to support heavy loads, and the protective walls are again made of wood strips; the Dislers use the terrace as an outdoor dining space in summer.

The really private “secret” space is up another two levels. On one side of the top floor are Disler’s daughters’ bedrooms. On the other, it is as if they have forgotten to add the top roof to the sloping mansard sides. This makes a perfect suntrap of a terrace, on which the girls can sunbathe. Any ideas their parents may have had about using the top garden have been quashed by the girls, who have squatters’ rights.

Disler admits the whole project was not cheap. “It was an opportunity for once in our lives to let go. I’ve indulged.” According to Paul Hehir, the project’s architect, estimated breakdowns of the costs came to £38,000 for the flooring, leadwork, mansarding and waterproofing of the top-floor terrace and £2,200 for the decking and support timber. The curved terrace on top of the extension cost £15,000 for the structure, £8,000 for the waterproof membrane roofing and £2,000 for the decking and timber cladding.

For Disler, it has all been worth it. As for the roof terraces, which allow not only views of the cityscape but also living plants on which to look out, they are, he says, “a green reminder”.

• KSR Architects, 020 7692 5000, www.ksra.co.uk
  
  
  

Explore Property

• Buying & Selling

• New Homes

• Overseas

• Interiors

• Investment

• Gardens

• Cool In Your Code

• Specials

• First-time buyer

Times recommends

• Second homes: credit crunch casualty or money-spinner?
• How I built my own sliding house
• Top 10 incentives for house buyers