When the thought of moving house makes you groan, but you're desperate for more room, what's the answer? For an increasing number of home owners, the solution lies beneath their feet.
Basement conversions, or excavations from scratch, are becoming all the rage in smart parts of London, with specialists reporting brisk business. Even in the countryside, if you have a listed property or need to accommodate a growing family but can't face the hassle of relocation, digging is on the rise.
"A lot of home owners find it more cost effective to extend their properties than to move," says Eric Morson of Basement Masters. His company has dug out new bedrooms, offices and 'big boys' rooms' with movie systems, pool tables and wine cellars all across London and the southeast. One recent project was a self-contained flat, excavated under a property in North London, for around £150,000 (see picture). "In the right area, this kind of flat could easily fetch £300,000," says Morson.
At around £2,500 per square metre, £150,000 is typical for an average 60 m² conversion, meaning that your existing property needs to be worth at least (say) £400,000 to make it viable. "Although we're finding that in areas like Bow, where prices are cheaper, people are still prepared to pay for basement extensions," says Morson. "If you have a leasehold apartment, you may be able to double the space, which is often worthwhile."
Owners of period listed houses in Hampshire and Surrey are among the clients for Jeremy Fisher Building, who has helped many homeowners dig deep. "By digging down, you can produce large contemporary spaces housing a music room, a playroom, or a large family kitchen that look as if they've been there forever," he says.
Among the super-rich, there seems to be an unofficial competition underway for who can build the most enormous, most extraordinary basement in London. Leading the pack is former property agent Jon Hunt, who made £370m when he sold Foxtons in 2007. His current plans for the eight-bedroom house he owns on Kensington Palace Gardens include a five-storey basement extension with room for a tennis court and vintage car museum. The completed scheme would run 180 feet into the back garden and a further 65 feet into the front garden, reaching a depth of more than 80 feet.
The planning application states that he needs additional floor space in order to "display vintage cars as pieces of art". This is, after all, London's most expensive street, with average prices standing at almost £22 million, despite an 18 per cent fall in the year to May 2009. Hunt allegedly turned down an offer of £200 million for his house from Aditya Mittal, son of the steel billionaire Lakshmi Mittal.
Close behind is JCB tycoon Anthony Bamford, who is looking to use some of his £2 billion wealth to redevelop Sloane House in Chelsea, installing an underground swimming pool, cinema and garage for his collection of vintage Bugattis. The Grade II listed Georgian mansion cost him £26.5 million in 2006, but he has run into difficulties after opposition from local objectors, including the Chelsea Society and the architect Joseph Rykwert.
The borough of Kensington and Chelsea is generally pretty relaxed about basement extensions. In the past couple of years more than 600 schemes have been approved.
But the potential difficulties for burrowers stretch well beyond planning issues. If any archaeological remains are found, you are obliged to call in experts to determine their value. Since new guidelines on archaeology and development were introduced in 2000 by the Heritage Council, it has cost developers and house builders around £25 million each year to evaluate and excavate remains.
Archaeologists are delighted, but homeowners faced with thousands of pounds in bills are less thrilled. "We budgeted for an archaeologist being there for two days," says Karen Briars, who was building a garage at her house in Bourton-on-the-Water in Gloucestershire. "But they found some pottery and meat bones, and realised that it was the kitchen of a large house, possible a Roman villa." In total, the team stayed for a week, costing her £2,000.
For large developers, the discovery of ancient remains can be turned into a public relations exercise, with developments such as Lord Palumbo's Number One Poultry in the City of London unearthing an entire street of 70 Roman era shops. Archaeologists were on site for two years, costing Palumbo at least £2 million.
Adjacent trees can be another sticking point, according to Richard Leatham of The Buying Solution. "Get a proper report confirming that this won't be an issue, and beware of underground rivers," he cautions.
The threat of flooding is certainly heightened when you dig deep, meaning that your walls may need to be tanked. As with any building work, you'll probably need to employ an architect, solicitor, surveyor, engineer, damp-proofing expert and builder to carry out the work. And remember that natural light will be limited, if there's any at all.
"Rooms that don't need windows, such as a gym, Turkish bath, wine cellar, media room or pool room are best suited to being hidden under the surface of the earth," notes Trevor Abrahamsohn of agents Glentree in northwest London.
Even the most bijou residences can be spruced up with a well-designed basement extension: one mews house in Grosvenor Crescent Mews in Belgravia was recently excavated to create a media room, Zen garden, laundry room, bar, library, steam room and gym, with a nine metre waterfall cascading from the first storey into the garden. Very tasteful.