Homes: Going underground

How would you like to increase the floor area of your two-storey house by 50 per cent, without an extension or converting your loft, and without appearing from the outside to make any changes at all? The answer is right under your feet. If that sounds like a riddle, then even more of one is this. Why, when a cellar can make such a huge difference to available space, have we been so slow to realise its potential in this country? We have been remarkably backwards in going downwards. True, there are plenty of Victorian houses with sizeable basements, but nowadays they are usually used for storing car-boot sale booty. Surely with a little imagination we could think of something more inspiring.

Some people are already doing so. The owner of a terraced house currently on the market in Fulham, west London, has created a large family-cum-kitchen- cum-dining room in what was an unused basement. The piece de resistance was the decision to remove the rear part of the ground floor above - a gallery where the ground floor ends now overlooks the basement below. It means the basement room is double-room height at one end and light floods in from above.

The Basement Development Group (BDG), which seeks to encourage us all to make more use of subterranean space, not surprisingly believes that basements are now absolutely of their time.

"With the increasing cost of building land, basements offer more usable space on a smaller `footprint'," says the BDG's Stephen Elliot. "Basements make full use of modern building design and techniques, so that they can provide the same environmental conditions as rooms above ground. And they are energy-efficient, which makes them relatively cheap to heat - not only because there is a large thermal mass but because heat, which travels upwards, will heat upper storeys." Then there is their sound insulation, a quality not lost on the neighbours of a musician in north-west London who installed a recording studio in his basement.

Increasingly there are signs that more developers of new homes are waking up to the possibilities of basements. Purpose-built for modern living, they incorporate all the right features from the start: large windows and French doors, with sites that slope away from the basement room to let in light. Figures from a study by the British Cement Association suggest that a house with a fully submerged basement costs only around 13 per cent more than a similar-sized property without one for a proportionately greater increase in space, a fact not lost on those taking the self-build route. Ruth and Jeremy Thorp, who edit the Self-Builder newsletter, say that they are seeing an increasing interest in basements and are currently building one themselves, which will have a workshop, two bedrooms and a playroom.

For people who can't start from scratch but still want to be creative, breathtaking effects can be achieved - but at a cost. Lindsay Cuthill, of estate agents FPD Savill, has seen a growing number of stylish basement conversions. "I talk to many builders who say `chuck me enough money and anything is possible', and many of the owners I have come across are prepared to spend at least pounds 40-50,000 on a basement conversion," says Mr Cuthill. The precise design and finish will obviously have a big bearing on the final cost of any work, but you should be prepared to spend a minimum of pounds 15,000. Key basics such as making sure the basement is well-constructed and, particularly, properly waterproofed don't come cheap. There is no real top limit on what you can spend. Cellar Conversions is currently working on a pounds 150,000 basement conversion in Hampstead, north London.

Some cellars convert more easily than others. "In some cases a basement runs the full length of the house, but in others there is only a narrow area of space under the stairs," says Mr Cuthill. Where this is the case, the space will have to be enlarged and that means excavation. But excavation is not only carried out to create a larger basement space. It may also be essential to deal with low ceilings. "A typical room height of 5ft- 6ft is not enough. What you need to create a real feeling of space is a minimum of 8ft, so you have to dig downwards to gain that extra space," says Mr Cuthill.

The size of your garden, front and back, is another consideration. "Some properties are better for digging out lightwells," he says. "You need at least eight feet in the front garden, and enough space at the back to allow you to dig a second rear lightwell. If you also happen to have a property that faces east-west, light will stream in from one or the other for most of the day."

If your subterranean space leaves a lot to be desired, you can still let your imagination loose - just what would you do in yours?

Basement Development Group: tel 01344 762676. Cellar Conversions: tel 0171 244 8585.

BARGAIN BASEMENT IDEAS

5 If the sight of yourself in a bikini is something you'd rather keep in the family, then turn your cellar into a swimming pool. To get the best calorie-busting effect install a wave machine and swim against the tide. Cost from pounds 80,000.

5 Create a candlelit dining room (this one is particularly good if you have exposed brick walls and pipes to create interesting shadows). Your dinner parties will take on a whole new feeling of intimacy.

5 Install a cinema. All the gear you need is readily available, and as cellars are easy to soundproof you can enjoy surround sound.

5 Grown-ups like furniture, but children prefer the floor, so give them a big playroom. They're less likely to bang their heads on the low ceilings.

5 Build a home recording studio. The neighbours won't notice the noise (hopefully) and one hit single should cover the cost.