Coffey Construction’s development at Carrigweir is testament to the growing awareness in the construction industry of the need to produce low energy buildings.
Funded under Sustainable Energy Ireland’s House of Tomorrow scheme, all houses are of steel-frame construction and incorporate high grade insulation together with heat recovery ventilation and individual exhaust air heat-pumps. Cathal Coleman of Coffey Construction says that there’s a substantial element of education involved in showing people around the show house. “They’re looking at the heat-pump and they’re half afraid of it. Other people come in and they don’t know anything about insulation or air tightness and they’re scratching their heads. But the minute you mention the cost savings to them, they come back and start talking to you. They’re worried about money at the end of the day, and in another few years, with the price of oil, they’ll do more worrying about it.”
The central innovation in the construction itself is the steel-frame, provided by Dryform in Portumna. “It’s the same as timber frame,” says Gerry McCarthy of the company, “but in steel frame, our biggest advantage is our strength to weight ratio over timber or traditional build…We like to say we probably have the best energy efficient house available on the market. Our U value is second to none.” He describes the structure as a ‘total warm frame’. 50mm polyisocyanurate (polyiso) panels are fitted to the outside of the frame in the factory, thereby eliminating the risk of cold-bridging. Moreover, because you’re not relying on site labour to insulate the structure, the risk of poor workmanship at that stage of the build is also eliminated. In addition to the factory-fitted panels, Insulation Distributors in Dublin supplied 75mm of Rocksilk DriTherm cavity slab for use inside the polyiso. Rocksilk is a semi-rigid slab of non-combustible rock mineral wool with a water-repellent additive. “Our basic U value starts at 0.21 in the walls,” says McCarthy. “The overall thickness of the frame is 140mm, that’s including the frame and the insulation, and that’s 10mm less than the standard timber frame which has a U value of 0.27.” Similar to timber frame, steel has the advantage of facilitating fast, clean construction. “We need a raft foundation or a concrete transfer slab. That’s number one. Unlike timber frame we don’t build on top of block work. We have to have a solid structure to come off…Everything we do has a concrete floor. We supply a concrete floor to the first floor, second floor and third floor if needs be.”
Construction continues on the site of one of Ireland's largest low energy housing estates, where several houses are already completed.
Pitched roof and floor insulation were supplied by Ballytherm in Cavan. 80mm of polyiso in the floors lies just beneath underfloor heating pipes, while in the roof, 100mm of the same substance is fitted between rafters. The roofs were then dry lined using a 50mm slab also provided by Ballytherm, the slab created by bonding 38mm PI board onto the conventional 12.5mm gypsum slab. The windows, from Munster Joinery, also claim a high thermal performance: 24mm doubled glazed units with an argon fill delivering a U value of 1.9. “All the doors are double rebated and double sealed,” says Tim Quinlivan of Munster Joinery. “And the windows have an adjustable locking system.” For added security, the double glazed unit is bedded into a double sided tape, making it very difficult for an intruder to penetrate.
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