Built on an awkward site in Salthill, Co Galway, Ireland’s first semi-detached passive house development was designed to meet the needs of three generations of one family. Constructing on this tightly restricted site was a difficult undertaking for the contractor, Mannion Passive House Builders. However they rose to the challenge and built a passive certified building which is comfortable, warm and affordable to run.
Cyril Mannion of Passive House Builders explained how the decision to go passive only came after planning permission had been granted. When he came on board, the first job involved sitting down with the clients Michele and Karina Heaslip and carefully working through the plan to see how it might be adapted to the exacting demands of the passive house standard. The client had already optimised orientation, layout and glazing by positioning small windows to the front which faced north/east and large windows to the rear which faced south/west. There were however a large amount of roof lights, sliding doors and junctions. Passive house construction generally favours a simple design. For this project, the more complicated plan meant it required closer attention to the detailing in order to ensure the correct level of airtightness.
Achieving the passive standard airtightness minimum of 0.6 air changes per hour was quite a challenge. Both houses had a total of more than 35 panes of glass, three sets of sliding doors and six rooflights, in addition to a large number of wall, ceiling and floor junctions, all of which had to be sealed. Installing the airtightness layer, using membrane, tapes and plaster, meant that all the following trades had to be closely monitored to ensure no accidental penetrations compromised the airtightness test. In order to ensure that the airtightness barrier remained undamaged, Mannion recruited an airtightness foreman to be onsite at all times.
On each of their sites, Mannion Passive House Builders assign a Contracts Manager to head their team of experienced craftsmen. This is overseen by a weekly visit from a member of the management team to ensure the work complies with the contract and with the clients’ specifications. All the sub-contractors that work on their sites are vetted to ensure their capability and suitability to carry out the work. The suppliers of building products are chosen in consultation with the client to make sure quality products are used. All employees receive regular training in the form of workshops and external courses to ensure they remain knowledgeable about the best practice methods for constructing low energy buildings.
Designed ventilation is a vital component of a passive house. For this project, mechanical heat recovery ventilation (MVHR) systems were installed in each of the houses. Unnecessary penetrations of the airtight layer were prevented by placing all of the building’s mechanical and electrical services, the MVHR units and ductwork inside the building envelope.
The initial plan included the installation of condensing oil boilers as a back-up for space heating, but site restrictions meant that these plans had to be changed. For House A heat comes via an air-to-water heat pump while it was possible to fit the condensing oil boiler on House B. Furthermore, House B’s favourable orientation enabled the installation of solar thermal panels which contribute to the heating of the domestic hot water.
The project resulted in two low energy semi-detached buildings and two satisfied clients. “The house is comfortable and draught free,” says Michele Heaslip. “The electricity bills come to about €120 a month on average, which is quite good considering that we have no other utility bills and we do a lot of laundry and cooking, and we have a home office. With the solar panels we don’t need to worry about hot water for six months of the year and as we have a water harvester we should never have to concern ourselves regarding water rates.”