Look up when buying a home: a room's height is as important as its footprint, making the "cubic space" a good measure of its true value, with high ceilings offering much more dramatic and inviting interiors.
Smart homebuyers who have become aware of looking for and comparing pounds per square foot the method traditionally used by developers and surveyors are opening their eyes to the joys and advantages of calculating price by pounds per cubic foot.
When estate agents and builders use square footage in property descriptions it applies merely to the home's floor area, or "footprint". The length and width of each room is multiplied and then totalled up, without any allowance for height.
To get the cubic area, the square footage is multiplied by height. So a 1,500sq ft apartment with 10ft-high ceilings would be 15,000 cubic feet. But the same 1,500sq ft footprint with 20ft high ceilings would be 30,000 cubic ft, double the volume.
With ultra-expensive luxury homes people are prepared to pay for the aesthetic qualities of "unusable" space, such as a triple-height atrium. Loft aficionados also treasure the architectural beauty of high, light-filled interiors with voids.
But these voids are also a great opportunity for expansion: when ceilings are high enough to accommodate another floor level, developers often squeeze in mezzanines say, for a bed deck to increase the saleable area (more square footage equals more money).
Today's new builds rarely come with impressively high ceilings (2.4 metres, or eight feet, is the regulation height), meaning that most of the homes offering exceptionally generous cubic space are conversions and refurbishments of old mansions and commercial, institutional and industrial buildings: Victorian schools and asylums, Georgian churches and chapels, banks, barns, garages, warehouses, workshops and interwar factories.
Some agents specialising in this sector say it is time for a new valuation method. "Perhaps a better benchmark would be to quote prices in pounds per cubic foot. However, it does require buyers to have an understanding of space," says Paul Wright, a surveyor with north London-based contractor Lynch Projects.
Environmentalists' demands for more sophisticated energy ratings may bring this about sooner rather than later as a home's energy efficiency and heat requirements cannot be determined by square footage calculations alone.
Already cubic dimensions are used by UK planning authorities when determining whether a home extension falls under "permitted development" rules. Normally, new extensions or attic conversions of up to 50 cubic metres do not require planning consent, depending on the size of the original house.
Clever architectural thinking can dramatically increase redundant cubic space
Hogarth Architects increased the size of an apartment at Queens Gate Terrace, Kensington, by nearly 40 per cent by adding a mezzanine. The 4.5metre-high apartment, formerly the grand reception room of a mid-19th century townhouse before it was split into flats, retains ornate cornicing and the original fireplace.
The single open-plan space has a fabulous oak mezzanine with bespoke shelving and staircase leading to a bedroom with en-suite bathroom screened by frosted glass. The mezzanine addition has added £500,000 to the sale price of £1.99 million, extending the apartment to 1,316 sq ft. Contact Douglas & Gordon on 020 7581 1152.
Architect Paul Brookes, a veteran of more than a dozen London Board school conversions, has even lowered floors and created yet more height by installing a replacement floor made of wafer-thin material used in aircraft production.
Ormond Yard, tucked away behind a wide barn-style door entrance in historic St James's, used to be the pumphouse for Chatham House, the famous nearby listed mansion, home to three former prime ministers. Niche developer Jonathan Brewin has transformed the space into a superb one-off residence using glass, steel, slate, stone, timber and Corian finishes. The showpiece feature is a void space spanning three floors crowned by a remote-controlled retractable roof.
Estate agent Lawrence Glynn describes the property as "mould-breaking", while the marketing brochure points out that the interior measures 1,763sq ft "without the void". Price: £2.49 million. Call LDG on 020 27580 1010.
Behind the retained classical façade of The Lancasters, overlooking Hyde Park, are 72 prestige new-build apartments, some with six-metre-high ceilings. Mezzanines have been built in to optimise space in the less formal rooms. A 2,862sq ft show home includes a 969sq ft mezzanine, "liberating" 34 per cent extra space. Prices from £900,000 to £17 million. Call 020 7402 8822.
Domus Nova, an agent specialising in architectural interiors, has a number of spectacular London properties on its books and is a worthwhile starting point. A double-height contemporary-design home in Gunter Grove, Kensington, has been built in two halves, connected by a glass bridge across a central atrium. Price £3.59 million. Call 020 7727 1717.
High interiors do not always come with a high price tag. The Paragon, a Victorian school conversion close to Elephant & Castle in south-east London, has some of the capital's cheapest double-height spaces. Prices from £595,000. Call Stirling Ackroyd on 020 7940 3862.
Such volumetric homes are not confined to London
Barns are the rural equivalent of factory lofts and can be transformed into terrific spaces, with "cathedral" ceilings and full-height glazed sections. Developer City & Country specialises in converting heritage buildings stable blocks, mansions, asylums and colleges keeping the raw beauty of the original structure and adding some metropolitan interior design touches to give a "country cool" look.
"There's real appetite for these sorts of homes because they've got genuine wow factor," says Helen Moore, managing director.
Hertfordshire and Essex are City & Country's favourite counties as both are close enough to the capital to entice both London commuters and people who want to leave The Smoke for good. Current projects include The Galleries, formerly Warley Hospital, in Brentwood, where a triple-height apartment has been created in the clocktower. Prices from £225,000. Call 01277 202122.
The same treatment is being given to Old Saint Michael's, a listed hospital in Braintree, where double-height apartments with exposed roof trusses are priced from £195,000. Call 01376 335800. Metropolitan Police inspector Phil Stinger, 28, was smitten by the double-height apartment he saw at Old Saint Michael's and had no hesitation about moving from a "bog standard new-build home".
"I love the fact that the original tall windows and structural beams remain unaltered and form part of the interior design," he said. "There's a liberating sense of space and the architectural character has real charm."
The Lakes near Lechlade in Gloucestershire is a 650-acre "eco-estate" where individually designed glass-and-timber houses are being built to order on the water's edge. The project is a collaboration between developers Yoo, backed by designers Philippe Starck and Jade Jagger, and Raven Group. Five clearwater lakes make up 60 per cent of the estate.
Buyers choose their plot, house style and interior design. Minimalist houses have American and Scandinavian design influences: open-plan, double-height spaces with floor-to-ceiling windows, decked terraces and boat landings. Prices from £870,000 to £3 million. Visit thelakesbyyoo.com or call 01367 250066.