Going deeper underground

Basement extensions are no longer the preserve of the super-rich – there are no limits to today's subterranean excavations as space-hungry city dwellers dig down

Business bosses and celebrities are going down in the world. About time too, you may think, but this is not because of the recession – it's because they are creating basements in their multi-million pound homes.

Jon Hunt, who sold controversial estate agency Foxtons for £370m at the height of the property boom in 2007, is enlarging his original plans for a basement and now intends to add three storeys beneath his home in London's exclusive Kensington Palace Gardens. Why? To store his classic Ferraris and numerous sports cars.

While Chelsea football club chief executive Peter Kenyon is digging down in his Notting Hill Georgian townhouse, to install a subterranean kitchen and three extra living rooms. Yet glamorous Bond villian-style basements need not be the preserve of the rich and famous. When Nina Kingsmill Moore wanted more space for her expanding family, a basement was the obvious solution.

"We had a little girl already and twins on the way. We wanted play and living space so a loft conversion wasn't the answer," explains Kingsmill Moore, a former deputy head teacher.

Six months later, her new basement had added 25 per cent to the size of the four bedroom Victorian terraced house in Clapham, south London where she lives with her stockbroker husband Hugh and their three children. Their experience shows the need to use experts and exercise patience.

The house already had a small cellar but creating a full-blown basement required shifting hundreds of tonnes of soil, using high-spec drilling equipment and ensuring the newly-created space was tanked – that is, lined with a metal skin to deter damp.

"We had a great local builder but he wasn't confident about such a big job. So our architect found a specialist company," says Kingsmill Moore.

After two and a half months of digging through the small front garden and the existing cellar, space was created to install a conveyor belt to help shift soil more speedily. Then the void was tanked and a large living room and bathroom were created.

"It cost £150,000 in total. There were lots of meetings with the council to agree plans, the noise was horrendous and there was a fair bit of dust but the disruption wasn't major," explains Kingsmill Moore.

The London Basement Company, whose client base has increased by around 75 per cent over the last five years, say basements typically cost £250-£350 per square foot. While estate agents say the value added to a property will usually exceed the costs.

Simon Albertini of estate agent Friend & Falcke says creating extra space broadens the appeal of a terraced house and is a good alternative to moving for those who are deterred by the housing slump. He says: "It's extremely attractive given the current fashion for relaxed entertaining and open-plan living."

There can be pitfalls however, especially if the work is done on the cheap.

"In extreme cases a poorly waterproofed basement can be subject to catastrophic flooding. More often simple dampness of the atmosphere can make the space cold," warns Yasmin Chopin of Property Care Association.

But basements are often the only way of creating extra space where there is dense older housing or conservation areas and listed buildings that restrict loft and sideways extensions – for example, Kensington & Chelsea council in central London approved 396 subterranean developments between February 2007 and May this year.

And now the basement phenomenon is catching on outside of London.

Peter Sheldon, a children's bookseller, has lived in his Regency terraced house in Edgbaston, Birmingham, for 20 years but it was only in 2004 that he decided to turn his disused cellar into a two-room basement.

"In centuries past the cellar was used for hanging beef and pork, and there was also a small coal chute. Gas and electricity came in there so we blocked that off as it was easier than moving the pipes. Then we tanked the place so now the space has been transformed into two rooms," says Peter, who designed the basement himself.

The project cost £10,000 and the two new rooms add about 28 sqm of living space, or the equivalent of one complete storey, to the size of his three-bedroom home. The coal chute has been augmented with glass bricks to allow in some natural light, while the area has been fitted with electricity and internet access.

"I love going down to my creation. It's marvellous to feel that what used to be disused is now a usable space that's increased the size of my home," explains Sheldon. "But then, I suppose that's the whole point of basements."

Nina Kingsmill Moore’s house is on sale for £899,950 through Cluttons, www.cluttons.com, 020 7223 7574; Peter Sheldon’s house is on sale for £335,000 through Connells, www.connells.co.uk, 0121 426 2800.