Scaffold littered back gardens across suburbia have become as common a sight as inner city cranes thanks to the building boom that has gripped the State in recent years.

Thousands of houses are now sporting salubrious conservatories, spacious lounges and extra en suite bedrooms that have been added on at a cost of anything from £15,000 to £60,000.

Extensions, while causing major headaches for some homeowners, have become the most cost-effective way of gaining more living space.

Spiralling property prices are cited by the building industry as the main reason why demand for extensions and garage and attic conversions has increased so dramatically over the past few years.

Those who want increased space and comfort but cannot afford to trade-up, are finding it is more practical to have work done on their own homes. In addition, lower interest rates now mean they can afford to borrow more money to fund such building projects.

According to one builder benefiting from the boom, the average profile of householders involved is middle class double income earners with a growing family. He said that in the majority of cases banks loan most of the cost but some are funded through inherited money.

Unfortunately, for many successfully completed home improvement schemes there are horror stories that feature shoddy workmanship carried out by fly-by-night builders who charge over the odds for their services and finish the work much later than agreed - if at all.

While there has to be a certain amount of trust between builder and home-owner there are steps that can ensure the process is relatively painless.

Not surprisingly, Dublin-based architect, Mr Anthony Brabazon's first tip for anyone thinking of getting an extension is to employ the services of an architect. And while there is a touch of he-would-say-that-wouldn't-he about his suggestion, there are considerable advantages in having such an expert on your side.

According to Mr Brabazon, the architect, like the builder, should be someone known and trusted by the home-owner. Alternatively the Royal Institute of Architects of Ireland (RIAI) provides a referral service where they offer the names of specialists most suited to the project involved.

Normally, the architect meets the client in their home to discuss their needs after which he prepares a design of the proposed extension and seeks planning permission if required.

Next the work is put out to public tender and when a builder is chosen a contract is drawn up between him and the home-owner which both parties sign. The architect acts as a kind of overseer ensuring that any payments are certified and the builder keeps to the exact work specifications as set down in the contract.

It is worth noting that due to the level of demand at present, the length of time between first contacting an architect and waving goodbye to the builders can be anything up to a year.

"The most important thing," said Mr Brabazon, "is that the builder is not overpaid at any stage because if he disappears this leaves the client exposed". Contracts should provide for retention money which typically covers the cost of any defects which show up in the first six months after the work is completed.

"Even if you don't go with an architect it is vital that you have reasonable drawings of the proposed extension and a proper contract stipulating specifically what is in and what is out in terms of the work," said Mr Brabazon. "If decoration is included in the price, for example, the builder may be thinking about a few coats of emulsion and not the Laura Ashley wallpaper the client has in mind."

In other words, problems are inevitable when the client thinks they are buying a Rolls Royce and the builder believes he is selling them a Mini.

Celbridge, Co Kildare-based builder, Mr Brian Gallagher and partner, Mr Gerry Duane, have been constantly busy carrying out extension work in the Dublin area since they formed their company, Forelock Construction, two years ago.

According to Mr Gallagher, there is a definite domino effect, with one job he completed recently leading to three similar extension projects for the firm in the same area.

He acknowledged that as demand was now exceeding supply, the cost of such projects was rising. Until recently the traditional figure taken to be typical guide when calculating building costs was £40 per square foot, but one industry source suggested this has more than doubled in the past few years.

Mr Gallagher stressed the importance of viewing previous work carried out by a builder and checking that they are reputable.

While most builders who work on extension projects are small outfits and not members of the Construction Industry Federation there are other ways of assessing their bona fides.

They should be registered for VAT (if they are not it suggests a low turnover), while agreeing to cash deals may compromise the home-owner at a later date. The builder should also have insurance for Employers Liability, All Risks and Public Liability.

The story of one man who got more than he bargained for when he extended his home underlines what can happen when corners are cut. The man eliminated the architect fees by negotiating directly with the builder himself. There were no drawings of the proposed design of the extension and there was no contract. All aspects of the deal, including price, were agreed over the phone.

When the job was almost completed it transpired that the builder had been paid too much and that much of the work was seriously defective. The home-owner was left to pay more money in order to rectify the mistakes and is facing the prospect of pursuing the builder through the courts.

A spokesman for the Office of the Director of Consumer Affairs advised home-owners to use common sense in all such dealings but said that the public "are taking their chances in this as in almost everything else they do".

Perhaps the best advice can be found in a saying that has become a mantra for those urging caution in the current boom climate: Buy cheap, cry often, they say, buy expensive, cry just once.