Narrabundahaus Passive
Description: Narrabundahaus
Building Type: Detached single family house
Location: Narrabundah, ACT, 2604
Number of Apartments/Units: 1
Treated Floor Area According to PHPP: 169m2
Construction Type: Slab on ground, timber framed with a combination of metal and brick veneer cladding
Year of Construction: 2021
Background and Brief
Narrabundahaus was designed to meet the Passivhaus standard from the very beginning. Having lived in numerous poorly performing homes over the years, the owners wanted confidence that their new home would be comfortable during Canberra’s cold winters and increasingly hot summers…without relying heavily on heating and cooling systems. Increased insulation combined with heat recovery ventilation and an exceptional airtightness of 0.18 ACH allows this home to maintain very comfortable conditions. Filtered fresh air is constantly supplied to all habitable rooms via a heat exchanger which can recover up to 96% of the indoor air’s heat, using this to pre-heat the outdoor air. The temperature generally sits between 20-22°C. The modelling has been stress-tested using a 2050 climate data set based on the IPCC A2 emissions scenario, ensuring that there is no risk of overheating in a warming climate. Perhaps not unsurprisingly the home is also significantly quieter than more standard construction.
The deliberately simple form allows the use of cost-effective construction systems and also eliminates complicated junctions which can compromise thermal performance. The planning was strongly influenced by the attached greenhouse which is positioned to the north where it receives maximum sunlight. Retaining the established trees to the north was both a constraint and a wonderful opportunity. Rather than dedicated (and seldom used) extra bedrooms, several flexible spaces have been incorporated which can be adapted to suit different scenarios. The studio is currently being used as a home office during lockdown and as an extra living space. The multipurpose room is normally used as a reading and stretching room, but is currently being used as guest room for the immediate future. It has a fold-out bed, adjacent bathroom and ample storage. It can be closed off with full height sliding panels or opened up to the rest of the living area. The attached greenhouse not only provides the opportunity for year round food production, but it is also a biophilic sanctuary with proven health and wellbeing benefits.
Over 10,000 locally made Canberra bricks were salvaged from the original cottage and re-used as a feature throughout the new construction. Not only does this reduce the embodied energy of the home, but it also responds to the surrounding context where these bricks are commonplace. Together with traditional corrugated steel cladding the external materials palette is durable and low-maintenance. The light colour also helps to reduce summer cooling demands.
Capturing water from the entire roof was a priority and this lead to the inclusion of two water tanks with a combined capacity of 10,000 litres. The larger roof feeds the larger tank which supplies water to the greenhouse and for general garden use. The other tank is connected to the laundry and is reticulated so that a potential future irrigation system can be connected if required.
Energy consumption has been reduced to a practical minimum, without compromising on comfort or amenity. A relatively modest 6.6 kW solar system enables this home to generate significantly more energy than it consumes on an annual basis. And the inclusion of a 14 kWh battery allows peak energy demand in the evening to be met and further reduces reliance on the electricity grid. More information and photos are available on the property here.
Challenges Faced
While the house has been occupied since April 2021, there are various items of work which remain outstanding almost a year later. The Covid pandemic is probably indirectly responsible for much of this. The best example is that the greenhouse isn't yet operational because the contractors are based in Perth and final commissioning has been delayed due to the quarantine requirements of the WA government.
Favourite Features
It feels like a sanctuary, which is the result of several characteristics. It's been warm in winter and cool in summer. And it's very quiet when we want it to be. In the current climate of working from home being able to so effortlessly control our indoor environment is fantastic.
The Design/Build Process
It's obviously an advantage to have a builder with Passivhaus experience. But that's not always possible and it wasn't for this project. Consequently the construction system was deliberately kept simple so that the selected builder would feel relatively comfortable with the project despite the Passivhaus ambitions. This was a way to de-risk the project in terms of budget and in particular the airtightness. It's a very simple concrete slab on ground with timber wall framing built on site and standard trusses. But it was an ongoing process to challenge the builders to think about doing all the small things better from a thermal performance perspective. To their credit the team achieved a fantastic airtightness test of 0.18 ACH.
The Brief
As an architect designing his own home, the brief was somewhat fluid. There were two primary requirements...the home had to be Passivhaus and there had to be a greenhouse for the resident horticulturalist. While the home is very much a bespoke design to suit the requirements of my wife and I, there are a variety of flexible spaces that can be used for living, working and sleeping depending on the circumstances.
Thermal Envelope
Exterior Walls: 140mm timber framed with R4.0 glasswool insulation and brick and Colorbond metal cladding.
U-value: 0.205 W/(m2K)
Roof: Timber trusses with R7.0 blow-in glasswool insulation and Colorbond metal cladding.
U-value: 0.136 W/(m2K)
Floor: Concrete slab on 100mm XPS insulation.
U-value: 0.264 W/(m2K)
Glazing U-value: 0.6 W/(m2K)
G-value = 0.5
Project Members
Architecture & PHPP: Michael Tolhurst Architect
Builder: Walmsley Building Solutions
Certifier: Clare Parry