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Stuart Street Certified Passivhaus

Located on a central city site overlooking the Dunedin harbour, this house has recently become the first house in Dunedin, to be certified under the rigorous International Passivhaus Standard. The home has been carefully designed and detailed to maintain a comfortable indoor temperature of around 20-22 degrees all year around whilst reducing heating costs by around 90% over a code minimum build.

In order to ensure this outcome the building design was modelled using the Passivhaus energy modelling tool. Based on the results of the modelling the design was modified and adjusted until the desired performance was achieved. This provided certainly around the final thermal performance of the building and facilitated for optimisation of windows and insulation.

The home was built by Caldwell and Highsted builders. The walls of the home were constructed using 142mm thick Kingspan TEK ‘Structural Insulated Panels’ installed by Kia Kaha builders of Wanaka. These panels provide insulation values around 3 times higher than current building code minimums. Quality timber window frames from Ecowindows of Raglan combined with high performance glazing drastically reduce heat losses through the windows and doors.  A solid layer of insulation under the timber floor on the ground floor creates a continuous thermal bridge free connection to the wall construction. The roofs are constructed using timber trusses with 300mm of fibreglass batts. An airtight membrane under the bottom chord of the trusses creates a draught free roof assembly.

In place of an expensive heating system the home has also been fitted with a Zehnder Comfoair 350 mechanical ventilation system with heat recovery. This system continuously draws stale humid air from bathroom and kitchen areas and supplies fresh pre-warmed air to bedrooms and living areas. The out-going stale air is passed through the heat recovery system and the heat is removed before being exhausted from the building. This heat is then passed to the incoming fresh air, resulting in a supply of fresh preheated air and very low energy losses. This approach ensures that even on the coldest Dunedin night there is always a constant supply of fresh conditioned air supplied to each of the bedrooms and living spaces in the house.

Every junction in the external envelope has been carefully designed and constructed to be airtight and thermal bridge free. This eliminates draughts and air infiltration from outside. The airtightness of the building envelope was verified during the construction process using a blower door test, which involves fitting a large fan to a door of the house and pressurising the depressurising the building. During this process any penetrations in the airtightness layer can be located and remedied before the linings are applied. A further blower door test is also required once the building is complete to ensure that the building meets the standard required for passivhaus certification.

Space heating for the house has been calculated at 14kWh/m2/yr. This means each year each square metre of floor area will require a mere 14 kilowatt hours of energy to maintain an indoor air temp of 20-22C. To put this in perspective a house built to the NZ building code minimums would require around 150kWh/m2/yr and even then there would be severe problems with humidity, condensation, mould and draughts.

 

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