Estate agents, parents, friends - and usually this column - all tend to have one word for twenty-and-thirtysomethings poised on the edge of the housing market - and that is, jump. Buy a house now if you possibly can, we advise. But there is a fundamental question to be asked, and that is - do you really want to buy a house?

It applies particularly to younger buyers, and single people who may find swapping the city lifestyle for a nest in the suburbs - or a comfortable flat for the tiny city apartment they can afford - too much to bear, even if it makes financial sense.

For many buyers, the impetus comes from without rather than from within. Getting marching orders from a landlord or finding that a flatmate is moving out are reasons some buyers opt to grasp for the bottom rung of the ladder. Everyone says that a mortgage is just as cheap as rent. But people don't count the real cost of what they invest in a home they call their own.

For starters, it costs money to buy and sell a house, as much as 8 per cent of the price of the house, in the shape of stamp duty, agent's and solicitor's fees and the like. On a £100,000 house, that's £8,000. If you're unhappy with your decision, it's an expensive mistake, as personal finance expert Brian Moloney of Moloney Mortgages, Pensions and Investments points out.

And in an inflated market like this one, you could easily make a mistake. Houses popular with young buyers - the Stoneybatter/Ringsend redbrick style of houses, or local authority houses in a three-mile radius of the city centre - are so hotly sought after that you don't get much time to make up your mind. You could end up buying a hovel that you can't afford to renovate properly, or a suburban house so distant it kills your social life stone dead. And if you're still in it when the property market slows down, you might be stuck there.

(One woman who bought and sold a house in the 1980s tells a cautionary tale: she bought a home by herself in an area now considered very chic, not far from the city centre. But the then drugs problem fuelled crime in the area. She suffered several burglaries; most of all, she missed her circle of friends, most of whom still lived on the other side of the city. She ended by selling at the wrong time, before rising prices could compensate for the troubles). Buying a house that will be your home solely for its investment potential is like marrying a man for his money. It's great when you're in love as well but if not . . . it's hell on earth.

It is becoming more and more expensive to purchase a house, even with low interest rates, because buyers have to borrow so much. There is the risk, Brian Moloney points out, that you are getting involved in an inflated market. And since Ireland has no control over monetary policy since the advent of the Euro, no one can really be sure that interest rates won't rise.

The point is that buying a house is a long term commitment: when property prices do stop rising (and this will happen sooner or later), you cannot be sure of selling readily, at the price you want, when you want. And as various financial pundits have pointed out recently, there are heavy financial penalties for defaulting on mortgage repayments.

You can, of course, take out a five-year fixed mortgage to guard against sudden rises in interest rates that might make your mortgage unaffordable. And if you really do want to buy a house, then arguments like those outlined shouldn't dissuade you. But if you're not sure, you should think very hard before moving out of rented accommodation in an area you like to buy a property you may not be altogether convinced about. Location represents a way of life, and it usually cheaper to rent in a popular area than to buy there.

(The Catch 22 here of course is that there is no really stable rental market in Dublin's capital, and many tenants are realistic to fear sudden increases. But there are landlords who are grateful for good, reliable tenants, who won't put up rents too suddenly, and with luck, you might get such a landlord.)

On top of the cost of borrowing money, there are all the other costs associated with house purchase: few people, when selling a home, calculate the cost of carpets bought and left behind, or of kitchen equipment, the pots of paint, curtain rails, patio slabs, plants and garden improvements.

Interest rates may be lower than ever before, but you are still taking on a debt by buying a house. The capital sum is not being given out for nothing. And this means that you will have to maintain a certain level of income for the next 20 years. Don't get trapped. Think twice if you have a grasshopper approach to the working life.

Maybe you really do want to sell computers over the phone just now but three months down the line you might want a stint on a kibbutz - or to go to college and study psychology.

So think before you buy. There is money to be made in property - but usually only over time. Traditionally, homes were bought by couples. Increasingly, young singles are taking the plunge but some no sooner get the nesting instinct and buy their own place when they meet their soul mate; needs change or the partner doesn't like your precious pad and the for sale sign is up before repayments have even begun on the capital sum.