Galway city Passive House
Passive House Builders built the country's first semi-detached passive house last year 2011. The project, completed in ten months, challenged us in a number of ways. For one thing, access was really, really tight. Our clients, Karina and Michele Heaslip, owned an existing house on site. The foundations of this structure were however too poor to make refurbishment an option. We had no choice but to demolish in order to make way for two independent, semi-detached homes.
During the demolition, we segregated the material and took everything – right down to the foundations - away in skips. Because of the access issues, planning was particularly important on this project; several jobs normally left to the end of the build had to be brought forward. All of the topsoil and rocks for rockeries went in first, as did the tank for the rainwater harvesting system.
Once construction actually began, access was reduced to only 1m on either side of the building.
The house itself, designed by owner/architect Karina Heaslip, was not originally intended as passive house. We sat down with the clients and methodically worked through the plan, to see how it could be adapted to achieve the more exacting requirements of a passive build.
They wanted both houses to follow the sloping contours of the site, which meant a stepped foundation. In order to eliminate cold bridges – which is absolutely vital in passive house construction – we installed a high density EPS (expanded polystyrene) foundation, which is completely thermal bridge free, and which gives a U value of 0.11w/m2/k
The house is built of masonry blocks, which are then wrapped in external insulation, delivering a U value of 0.10w/m2/k. The external surface is then finished with an acrylic render, giving it the appearance of a conventional cement plaster finish.
Making the most of passive solar gains is also very important in passive design. The client had already optimised orientation, layout and glazing; positioning small windows to the front-facing north/east and large expanses of glass to the rear-facing south/west. We also reduced the number of roof-lights, and upgraded the windows to Passivhaus certified units.
Though one heating system would have been sufficient for both houses, we installed two separate systems in order to keep them independent. A condensing oil boiler was installed in House A, though space restrictions in House B meant that that wasn't an option, and instead, Michele and Karina opted for a Stiebel Eltron heat pump.
Making sure there are no uncontrolled air leakages is another vital element of passive house construction, and requires a high level of co-operation from all trades throughout the build. We had an airtightness foreman onsite at all times, making sure that the air tightness barrier remained undamaged.
This was a difficult house to achieve air-tightness in. Between both houses, there were more than 35 panes of glass, three sets of sliding doors and eight Velux windows, as well as numerous wall, ceiling and floor junctions, all of which had to be sealed. But our hard work paid off. The air change rate of 0.6 ACH is just on the Passive House threshold, but still a very impressive rating for a house of this nature.
You can't have air tightness without heat recovery ventilation. In this case, we installed and commissioned a Paul Novus 300 in house A and a Paul Focus 200 unit in house B, both from Paul in Germany, and both certified passive house units.
'We found the Passive House Builders team very efficient.' Says owner Michele Heaslip. 'Though challenged by bad weather and a complex plan, the build was completed to our satisfaction within ten months. We'd highly recommend PHB for making every effort to achieve our comfortable, draught-free home which is finished to the highest standard.'
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Architectural work was by http://www.homespaceplanner.ie/
