Opus Developments has used the latest building and engineering methods in a scheme of 57 apartments, townhouses and duplexes in Newcastle, Co Dublin, which went on sale today.

And the developers say they have upped the energy efficiency standards of the scheme so radically that buyers can expect to halve their heating bills, as well as reducing CO2 emissions.

Energy efficiency is the latest buzz word among developers as the new EU directive on energy performance in buildings forces them radically to raise standards of insulation in new homes.

This new system rates how energy-efficient a building is and is designed to reduce the carbon emissions from household heating. The system will provide a grading system which all new homes built after January 2007 will have to undergo. A house with a high energy rating will, inevitably, be more attractive and worth more to buyers because it will be such an important indicator of how high their gas and oil bills are likely to be.

The energy rating will certify a house's ability to use energy efficiently, measuring how much heat is lost through poor insulation in walls, windows, roof or as a result of an inefficient heating boiler.

With this in mind, Opus has put a huge amount of thought and design into the energy efficiency of Castlelyon. A spokesman said the company is confident that the homes will achieve the maximum score under the new directive.

"Home energy ratings will brand dwellings in terms of energy use and running costs, " said the spokesman. "New homes built under the current building regulations would achieve an energy rating of no higher than D whereas at Castlelyon we expect to achieve a rating of A+".

Castlelyon is a development of one-, two-, three- and fourbed homes. Energy-efficiency features include high-performance insulation in the walls, floor and roof, an efficient heating boiler, and solar panels for hot water. Each house is also oriented for maximum sunshine and solar heat gain.

Houses that are insulated as well as those at Castlelyon also need what's called a heat recovery system. This captures heat generated within as it is leaves the house and is then used to warm up the fresh air which enters the house.

"This system of heat recovery removes the need to continuously reheat the same space while expensive energy flows out through air vents in the wall, " says Opus Developments. "This will result in massive savings on heating bills.

The provision of controlled airflow through the house also regulates humidity and prevents mould as well as eliminating allergens."

These are timber-frame homes and the timber used in their construction comes from managed forests. Opus is also using the most environmentally friendly specially-produced "GGBS" concrete in the foundations, again reducing CO2 emissions significantly.

The developer believes house values of the future will be hugely dependent on energy efficiency, especially because, as the seventh-most oil dependent nation in the world, we are so exposed to oil price fluctuations.

"The depletion of natural resources and the increasing costs of fuel have been discussed a lot in the media recently and house owners are becoming aware of the importance of energy efficiency, " says Ronan O'Driscoll of Hamilton Osborne King, sales agents for Castlelyon. "The running cost of these houses is less than half that of standard houses so it is inevitable they will be more valuable."

Under current building regulations, there is no requirement for new homes to get any of their energy from renewable resources. But Opus Developments expects buyers to become more energy-conscious when the new grading system starts next year.

"We don't feel buyers should have to wait for the government to make developers provide energy-efficient houses through legislation, nor do we feel they should be made to pay extra. We are bearing the significant additional cost of providing this technology on the basis that it is the right way forward both ethically and ecologically."

The development is in the village of Newcastle, just off the Naas Road near Citywest.

It's an area earmarked for expansion, governed by a village plan in agreement with South Dublin County Council and local residents. The aim is that new developments will be consistent with a traditional village and will include a 15acre park and a new school.

The commuter train to Dublin is five minutes away.

The Castlelyon development will be completed by February 2007 and is selling from the plans. Features include integrated fitted kitchens with Arated dishwasher, fitted wardrobes in the bedrooms, timber doors, wiring for broadband and solar panels.

Price: one- bedroom apartment (52 square metres) from 265,000; twobed duplex townhouse (82 square metres) from 335,000; three-bed townhouse (90.5 square metres) from 395,000; four-bed townhouse (119 square metres) from 490,000;

four-bed semi (121 square metres) from 25,000 Agent: Hamilton Osborne King (01-6181300)