Balconies are growing up, and out. They are becoming apartment dwellers’ latest must-have, with space for entertaining around the barbecue, and such indulgences as hot tubs — as seen in the Big Brother house.

Research by DTZ Residential shows that 70% of new homes in central London now come with a balcony, compared to just under 50% in 2000, and just 15% in 1995. They are also much wider. DTZ says balconies in new blocks of flats have roughly doubled in size in four years — to an average 8ft x 6ft, compared with an average 6ft x 4ft in the 2000 sounding.

Adam Gaymer, new homes director for DTZ Residential, says: “Outside space is the new big thing. Although our research covers only central London, I think the same trend is apparent across the UK.”

In Manchester’s new Macintosh Village development, Taylor Woodrow has apartments with roof terraces, but the eight town houses on the site also have outdoor roof space rather than a traditional back garden.

Also in Manchester, Urban Splash has introduced “stepped” buildings to maximise the potential for terraces. Builders see balconies as a relatively inexpensive add-on that helps them to compete in a congested market.

At Taylor Woodrow’s Bombay Wharf development in Rotherhithe, London, duplex apartments have only a single room on the upper level — customers would rather now have the rest of the space as a terrace.

“A roof terrace can probably add between 5% and 10% to the value of a property, depending on whether it faces southwest or not,” says Tim Wright, a partner at Knight Frank’s Kensington office. “A really big terrace might add as much as 15%.”

Even so, an empty balcony may not be enough. More are now being sold with power and lighting and a gas tap for the barbecue. Other extras include hot tubs, fountains and even pools, decking, topiary, lawns, “mood” lighting and floodlighting.

Ballymore Properties, in its New Providence Wharf scheme in London’s Docklands, was one of the first builders to make a sales feature of the fitted balcony. Every penthouse has an outdoor hot tub, and all sold off-plan.

Berkeley has taken the concept a stage further, renaming the balcony the “leisure deck” in its 10-storey development Senses, a scheme of 300 studio, one- and two-bed apartments, and three-bed penthouses off Queenstown Road at Battersea Park, currently being sold off-plan.

The studios have leisure decks of 5ft x 12ft; the one-bedroom decks are 5ft x 14ft. The penthouse and duplex decks (40ft x 13½ft) come with a hot tub behind frosted-glass screens for privacy.

DTZ calculates the theoretical value of the London apartment balcony, if sold on its own, at £25,000. It reached the figure by taking the square-foot value of the internal space, and extrapolating a proportion for the external space.

The balcony appeals up to about the 14th floor, where vertigo and wind reduce the attraction. At this level and upwards developers prefer covered or recessed balconies, as in the Barbican or 100 Westminster Bridge Road — the Crest Nicholson conversion of the former MI6 building in Waterloo, now all sold.

With several very high London schemes on the drawing board, including the 29-storey Z Building on Deptford Strand by Berkeley Homes, and its 24-storey residential tower, Tabard Square, near London Bridge, architects will be looking to meet the new demand for balconies. George Wimpey City, at Falcon Wharf, a scheme overlooking the Thames at Battersea, is building 124 apartments with “winter gardens” — balconies shielded in glass for year-round use.

Additional reporting: Simon Brooke

Senses, Berkeley Homes, 01732 227 666; New Providence Wharf, two-bed apartments available from £440,000 from Ballymore Properties, 07000 701 701 or www.n-p-w.com; Falcon Wharf, from George Wimpey City, 020 7987 0500 or Hamptons International, 020 7244 4700

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