THEY are too hot in summer, they are too cold in the winter, and now - it seems - they lose cash all year round.
Conservatories, once a symbol of stylish living, have emerged as the biggest casualty in an authoritative new report into the do's and don'ts of upgrading your home for 21st-century buyers.
The report, by a leading housing economist, says that sellers are likely to lose money if they mistakenly build conservatories in a bid to increase the value of their homes. The structures, which are likely to cost at least 10,000 to build, probably add as little as 7,000 when it comes to selling on.
The money would, according to the experts, be better spent on converting a loft or a garage into either an extra bedroom or living room. Adding an extra bedroom will typically increase a home's value by 26,000 and an additional living room by 45,000.
Garages are also not the attraction they once were, the report points out. While they remain an asset, it is not because they are needed to house a car but because they provide potential space for an extra room.
Britain's reputation as a nation of gardeners also takes a blow. Gardens still add value to the overall price of a home, the report says, but surprisingly, only if they are not too big. While the modern generation of homebuyers like the idea of sitting outside with a glass of wine, they do not want to get their hands dirty.
The research, carried out by Professor Gwilym Pryce, a housing economist in Glasgow University's Department of Urban Studies, charts the changing preferences of housebuyers, reflected in the features or attributes for which they are prepared to pay extra.
Commissioned by the Glasgow Solicitors Property Centre, Pryce studied thousands of transactions over a seven-year period in the Strathclyde area.
By comparing the sales price of houses with certain features with those without, he was able to give each feature a precise monetary value and monitor how each changed over the period between 1999 and 2006.
The 1990s brought a boom in conservatory building, as more homeowners sought a halfway-house between their living rooms and their gardens. But whereas in 1999, a 10,000 conservatory would have added 14,000 to the value of your house, the equivalent figure now would be just 7,000, says Pryce.
"I'm afraid conservatories are pass as a means of increasing the value of your house whereas adding an extra room inside could be very lucrative," said Pryce.
The report says the added value of creating an extra public room has increased by 152% over the past seven years, from 18,000 to 45,500.
The research also established the growing extent to which an extra bedroom can increase a home's resale value. In houses, the added value of having an extra bedroom has risen from 12,000 in 1999 to as much as 29,000, an increase of 139%.
But the percentage rise in flats has been even bigger at 182%.
"Putting an extra room into a flat takes it into a different price league altogether," said Mark Hordern, the GSPC's marketing manager. "In houses that have three bedrooms, a fourth might not make all that much difference to a buyer, but it makes a huge difference in a flat as long as you do not take up too much public space in the process."
One method of creating extra space appears to be the increasing popularity of converting garages. "Garages are now where you keep your tools and the bits of old furniture from your granny that you don't want to throw away," Hordern said. "They are not where you keep your car. So owners are thinking, wouldn't it be better to convert the garage into more living space, and, according to the figures, this is a very good decision.
"Owners with double garages are converting one or part of one, leaving the other to perform a more traditional function."
David Alves, a partner in the Stewart Saunders property agency in Edinburgh, said he agreed with Pryce's findings. "I built a conservatory on my own house 10 years ago and it was often either too hot or too cold. I should have built something with a proper roof. Even if you build a small conservatory I doubt that now you would get your money back."
Gardens are another feature where the added value has decreased over the past seven years with, property agents say, many homeowners too busy to devote time to maintaining them. "Big gardens cost time and money," Alves said. "At this time of year, once you have filled the 80th plastic bag with dead leaves you feel positively suicidal. One trend I've noticed is that those who buy big gardens do it either to build a block of flats or knock down the existing house and build a bigger one. They do not want to garden."
Pryce was also able to work out the benefits of owning certain types of property.
One finding was that traditional detached bungalows had an 'added value' way in excess of detached villas of the same size. In 1999, that added value was worth 12,000, but by the end of 2005 this had soared to 40,000, an increase of 235%. Housing analysts believe this is because bungalows are ideal for loft conversions, giving the occupiers extra rooms while increasing resale value.
One factor that has not changed is that property prices in Scotland are still on an upward curve, with around a 10% increase in value expected at the end of 2006 despite dire predictions last week that the property "bubble" was about to burst.
Martin Ellis, chief economist with HBOS, said: "House prices will continue to grow because the fundamental factors that underpin them - such as strong economic growth, full employment and a surplus of demand over supply - are stable. This is not expected to change in the near future."