Property: It's dark, underground - and would like to enter your home

Bedroom, bathroom, wine store - a cellar can add a whole new room to your life.

WHEN STUART Jones, an estate agent with Westminster Properties, recently inspected a cellar in a north-west London property, he expected to find the all-too common dark, dank, rubbish-strewn area. Instead, he discovered a fully-equipped, hi-tech studio - the owner was a member of a band who had put the cellar to productive use.

Stephen Elliot of the Basement Development Group (BDG), would be impressed. The organisation promotes the use and development of the under-utilised space below ground. "At the very least, a cellar is a great storage resource," he says, "particularly in these minimalist times."

Resourceful cellar owners have been turning their cellar into a den, or an extra bedroom for guests. "We have seen quite a few examples of cellars being used in this way," says Nick Goble of the estate agents Winkworths in Battersea. It is, unsurprisingly, more common in one-bedroom flats, where extra space is at a premium. "In many cases though, the owners have not tanked the cellar properly."

Tanking is the process whereby the cellar is made watertight. "If the cellar is to provide living space, then you certainly need to protect it from penetrating dampness and mould growth," says Mr Elliot. "Even if you are just using it for storage, you don't want your stuff going mouldy." He advises consulting a surveyor to check for signs of damp, "and if you decide to go ahead with any work, use a builder who has sound experience in cellar work - contact the Federation of Master Builders for names."

Chris Evans, a development control manager at Bromley Borough Council, advises writing to your local authority with any plans early on, particularly if there is likely to be any structural change - a term which can cover merely installing a window. "Any work will need to comply with building regulations," he says.

The BDG produces several documents aimed at builders or rehabilitation specialists, which give advice and specifications for the basic through to what Mr Elliot terms "pukka" conversions. "You can introduce internal waterproofing, or incorporate additional ventilation and/or dehumidification," he says.

However, Mr Elliot warns of getting carried away: "You need to consider carefully the practicality of any work you do, as well as the cost. Finding out whether improvements in thermal performance or habitability, for example, can be achieved within your budget, is crucial".

While the word "cellar" is one that makes the eyes of many a buyer light up, it should not make pound signs flash. "We have had several properties where the cellar has been made into a bathroom," says Lisa Keating of Bushells estate agents in Clapham. However, taking into account the costs of tanking, tiling etc., there is clearly no large profit involved, putting around pounds 5,000 on the price of a pounds 120,000 flat. Nick Goble of Winkworths is cautious about such usage. "Downstairs bathrooms are not popular," he says, "and you have the difficulty of ensuring adequate ventilation in a cellar."

For many people, however, it is the opportunity of having a "real" wine cellar that lies in their yearning for a cellar. "When I bought this flat, I had looked at several properties, but it was the cellar that clinched the decision to buy it," says Nicholas Richards who lives in east London. "I love having a wine collection maturing in the cellar. "Wine cellar" has a certain social cachet about it, and a well maintained one may impress future buyers.

"One of the most impressive cellars I have seen was a wine cellar in a Victorian two-bedroom flat in Brondesbury," recalls Westminster's Stuart Jones. "The owners were serious wine lovers, so they knew all about temperature, light, and humidity control - and having no strong smells nearby. Usually I am tripping over half-used cans of paint and other chemicals in cellars, but this one was in pristine condition."

Ironically, given their damp image, some cellars can, perversely, be too dry and warm for keeping wine. One organisation, Norcool, produce door kits and refrigeration units that will maintain a constant, appropriate temperature within your existing cellar, "although you need to insulate the cellar", says Norcool's Christine Martin. "We can do this, or provide the necessary information for people to carry out the work themselves".

Even those in upper-floor, centrally heated apartments, need no longer be deprived of the joys of a cellar. Norcool will install a cool, moist "cellar" for storing and maturing wines almost anywhere in your property.

But will turning your spare bedroom into a giant fridge mean you are subjected to loud humming that keeps you awake at night? Apparently not. "The cooling unit has been designed to be low-noise", says Ms Martin.

And if a future buyer doesn't share your enthusiasm for your "upstairs cellar", you can remove the units and doors and take them with you.

Basement Waterproofing Design Guide, co-sponsored by the British Cement Association and the British structural Waterproofing Association, is available from the Basement Development Group, 01344 762676; Federation of Master Builders, 0171-242 7583; Norcool Appliances Ltd, 01302 751223. Door kits cost pounds 250-500, and refrigeration units around pounds 1,200; Winkworths estate agents, 0171-228 9265