Property: How to hothouse your money

A conservatory should be more than just a spare room for the dog's basket and the children's toys - and it can be a real investment.

A conservatory is proving to be this year's must-have, and could enhance and add considerably to the value of your home. Latest figures released by the National Conservatory Advisory Service (NCAS) show a 58 per cent increase in sales of conservatories for the first quarter of 1998, with a spend in the UK last year of pounds 250m.

NCAS director Richard Craig believes the current rise in house prices is a contributory factor to the growth in the market. "If people can't afford to move, they can draw on equity in the property to improve the house instead. Conservatories can be built to a very high specification and can create a very useable living space."

Whether you choose a conservatory to install a Jacuzzi, gym or just the dining table, tacking it on to the back of the sitting room is seen as a mistake. Richard Morgan, from Buckinghamshire estate agent Barringtons, has good advice. "A conservatory has to enhance the living space. Creating a breakfast room off the kitchen or a dining room where none exists is the best idea." And what of saleability? "They are a definite selling point if done properly and in sympathy with the property," adds Mr Morgan.

Runcorn Residential in south London is currently attracting great interest in a detached Victorian villa it is marketing, with a gothic style conservatory on two levels. The conservatory was rebuilt 10 years ago, and its unusual aspect, overlooking the large, secluded garden from the ground and first floors, is a major selling feature. Nicholas Runcorn comments: "On the first floor the conservatory is at the end of the rather grand entrance hall, so it's the first thing you see as you enter the house and the light just floods in." Offers on the property have gone to sealed bids, and are expected to be in excess of pounds 385,000. Without the conservatory Mr Runcorn estimates that the house, parts of which are in need of refurbishment, would have been valued at around pounds 50,000 less.

Three toddlers and a dog drove Lancashire residents Joanne and Alan Lockhart to think about a room that they could escape to without having to wade through a pile of toys. "We already have a spacious house," says Joanne, "but on the ground floor it's really one big room, so we decided to get some quotes for a conservatory."

For once, an unsolicited telephone call from conservatory company Anglian came at the right time. "I'd already had four quotes and I could see the quality was pretty much the same," said Joanne, "but as Anglian claimed to be offering 40 per cent off, I asked them to match the cheapest quote I had." They settled on an inclusive price of pounds 12,000 for a spacious, Victorian style glass conservatory, incorporating a dining and seating area. "We couldn't believe that it was finished in two weeks, and it's fantastic. We sit in there every evening."

A radiator provides heating during the winter but on really cold days they top up the temperature with an electric fire. "When it's really hot in the summer, we could do with blinds," adds Joanne, "but they cost a few thousand so we'll suffer for the time being." And a recent valuation of the house has shown that the Lockharts have more than recouped the cost of the addition.

But beware. Conservatories can also make your house difficult to sell and, in the case of a bad construction or inappropriate styling, knock a few thousand off the asking price. Baz Truman bought a house three years ago with a so-called conservatory. "It was a dog's dinner (apt, as the previous owner had kept a couple of Rottweilers in there). The market was dead, and no one wanted to buy the house because of it, so I got a great bargain, but there was no way the conservatory could stay. Getting rid of it was a nightmare."

As with many home improvements, recommendation is often the best way to choose a company. However, the NCAS offers free, independent advice and will try to arrange for you to inspect local constructions. An adviser visits your home to discuss the style, materials and building regulations. Drawings are then submitted to up to four of the 400 NCAS-registered firms whose accounts and installations have been checked. Tenders will be collated and discussed.

The NCAS will also advise on completion of the work and payment structures. Fixed fees charged to the company selected to do the work fund the NCAS, and are guaranteed not to be passed on to the consumer in the quote. Prices quoted will be lower than usual, as there is no commission payable to a sales person.

When the sky's the limit, a rooftop conservatory has to be the ultimate extension. You can't buy it, but the split level penthouse apartment overlooking central London's Russell Square with three bedrooms and conservatory opening on to a large roof terrace is for rent through Capital Asset Management for around pounds 1,200 a week.

National Conservatory Advisory Service 0500 522525; Runcorn Residential 0181-516 6585; Capital Asset Management 0171-736 5633; Barringtons 01753 880200