Designer: Harley Truong / Andrew Verri
Stage: Completed 2014
Location: Chifley, Canberra
Standard: Passivhaus Standard (certified)
Built in 2014 on a subdivided block in Canberra, this house is one of two side by side with nearly identical floorplans. One is a mirror image of the other. Both have attained Passivhaus certification from the Passivhaus Institute in Darmstadt Germany.
The house has a simple and compact floorplan with most of its windows facing north, bringing light and winter warmth into every living space. Facing north is not a strict requirement to meet the Passivhaus standard but with all that free winter heat from the sun, it makes it much easier.
High performance double glazed uPVC-framed windows and doors are used throughout. Once you see the quality of a European-styled tilt and turn window, you will never consider anything else. They seal up tightly when closed – like a car door. And if you have a high performance double or triple glazed window, you won’t feel cold standing next to it.
With the use of deep eaves, the low winter sun penetrates deep into the living room, but the high summer sun is completed blocked from entering the windows.
Motorised external blinds take care of the shoulder seasons when the weather is both hot and cold. These blinds block out 78% of the light and heat and being installed on the outside of the window, they actual work in stopping heat entering the house.
The bedrooms also face north but with much smaller windows. Solar gain isn’t as important in bedrooms because it is more comfortable to sleep with cooler temperatures.
The bathrooms are all located on the southern side and all have small windows mainly for light and cross ventilation. Given that the most expensive window, if located to the south, loses more heat than a well-built wall, it makes economic sense to minimise the glazing on the southern side of the house.
What is the right balance of glazing versus walls, double versus triple glazing? An energy model of the entire house using the Passive House Planning Package is the only definitive way of knowing.
In this photo, the high density polystyrene foam has just been laid ready for the reinforced concrete slab to go on top. The foam insulates the floor from the ground, which in Canberra, is around 15C in winter.
The result is that the floor is comfortable to walk on barefoot even thought the entire house is laid with porcelain tiles.
The roof panels are also insulated with foam. The foam contains a fire retardant and is 200mm thick giving an R-value of 5.
The wall panels are insulated with 90mm of Polyiso foam sandwiched between 15mm OSB sheets. Total R-value 3.4
Here the windows are being installed using expanding foam. The foam fills in the gaps and sets like polystyrene foam. It is cut with a bread knife and special airtight tape is used afterwards over the foam to ensure a long-lasting air seal. You only get one chance to get it right and the cost of foam and tape is small compared to the energy saved.
The white Intello wrap is a fabric that is stapled and taped to the walls before the plasterboard is installed. It acts as the all important air barrier. Special care is taken to join the fabric to the floor and ceiling and airtight tape is the best way to achieve a good seal.
In this photo, timber battens are used over the top of the Intello to create a service cavity for running electrical wires and water pipes.
Beware of alternative methods for air sealing. Plasterboard itself might be airtight but when installed, it almost always cracks at internal corners and cornices and leaks air through skirting boards, architraves, light fittings and power outlets.
Special care is taken to seal penetrations around electrical wires and plumbing pipes. There are well tested products on the market and techniques to ensure a long lasting air seal for any sized penetration.
A blower door test is the best way to verify airtightness. A test was conducted during the construction phase once all the windows and doors were installed to allow the opportunity to fix any problems before the plasterboard went on.
Some problems highlighted during the test were small tears in air tight fabric; gaps caused by the tape not sticking to areas of rough concrete; gaps around wires inside conduit piercing the air barrier; gaps around drainage pipes in the slab. They were all easy to fix on the spot but would have been impossible after the house was finished.
The final test result was 0.11 air changes per hour at 50Pa. This figure is 6 times better than the Passivhaus standard and about 100 times better than the average Canberra house.
With an airtight house like this, mechanical ventilation is a must. Fresh is brought into the house using a Zehnder Heat Recovery Ventilator (HRV). It only consumes 70 Watts of energy and runs all day long bringing in fresh air from the outside of the house and distributes it to all the living areas and bedrooms using ducting in the ceiling. At the same time, it removes stale air from the kitchen, laundry and bathrooms and expels it to the outside.
What is special about a HRV is that it uses a heat exchanger to take the heat from the old air and puts it into the new air, without ever mixing the air streams. On cold mornings when it is -5C outside, the outgoing air heats up the incoming air to 16C without any additional electricity besides the fans. The heat exchanger is 92% efficient at doing this.
Another bonus is that the incoming air is filtered with a 1 micon filter to remove pollen, dust and pollutants – perfect for hayfever sufferers and asthmatics.
Yet another feature of the HRV is that if you hang your clothes to dry inside the laundry on a clothes horse, it almost always dries in 24 hours, even in winter. This is because any excess humidity is continuously being removed. You won’t need a tumble dryer anymore.
So although it might seem like a burden to have to install mechanical ventilation, it is actually a very neat feature of the house. It is ideal for busy families who aren’t home to open the windows for ventilation, for those living near busy roads who don’t want traffic noise inside their house and for those who appreciate clean air free of insects, pollen and pollutants.
Passivhaus homes, by definition, only require a maximum of 15kWh of heating per m2 of floor area each year to maintain a 20C minimum in every room. The idea is that Passivhaus homes are so well insulated and sealed that the heating system required is tiny compared to a conventional house.
In this house the heating system is a $300 1.2kW electric heater that consumes as much power as a hair dryer. The photo here shows the heater installed on the output of the HRV unit just before it is distributed to all the living areas and bedrooms. It never heats the air in the ducts above 50C so you never get that burnt dust smell that is typical of ducted gas heaters.
The kitchen has an electric induction cooktop. Most people think they have to have gas cooking but in reality, an induction cooktop can heat water even faster, is a breeze to clean afterwards and is safer around children because it doesn’t hold much residual heat. Moreover, it compliments that minimalist look that people are after these days. A benefit of electric cooking is that the house no longer needs a gas connection. The gas service from the street was disconnected when the house was built. And good riddence to quarterly gas connection charges.
Another unusual feature of the kitchen, but common for passivhaus homes, is that the rangehood recirculates air back into the kitchen rather an expelling directly to the outside. If it did expel the air to the outside at a rate of 500-1000 m3/hr, like in a conventional houses, then the same volume of air will be sucked into the house from somewhere else. It would have to such cold air through an open window or worse it would probably come in through downlights, and cracks in the walls, bringing with it dust and other pollutants.
In this house the air is filtered 3 times to trap moisture, grease and some of the smell before filling the kitchen. The whole-house ventilation system then kicks in and is very effective in removing all of the stale air in about 20 minutes. A wireless booster switch is located in the kitchen to temporarily bump the ventilation rate from the normal 100m3/hr to the maximum rate of 250m3/hr – with heat recovery working the whole time.
Hot water is produces using a Sanden electric heat pump. The stainless steel tank is located in the laundry and the condenser is located immediately outside. It works just like an air conditioner to draw the heat out of the ambient air outside and puts that energy into the water to heat it up. On a warm day, every kWh of electricty used puts 4.5 kWh of energy into the water – 4.5 times better than a standard electric hot water heater.
Installation is easy and cheap too because the refrigerant is internal to the condenser and so only a plumber and electrician are needed.
The electricity bill here shows how economical it is to run a Passivhaus.
2014 Summer, $211 for 882 kWh over 88 days.
2015 Autumn, $214 for 1031 kWh over 77 days.
2015 Winter, $275 for 1445 kWh over 91 days.
2015 Spring, $258 for 1269 kWh over 99 days.
2016 Summer, $214 for 945 kWh over 93 days.
2016 Autumn, $209 for 936 kWh over 89 days.
2016 Winter, $301 for 1508 kWh over 88 days.
An environmental monitoring system is used in the house to record temperature, humidity and energy usage.
The results of the house monitoring system are viewable live on this website.
Over the 2015 winter period, the house mostly stayed above 20C even when it was a frosty -4C outside. Occasionally it dropped down to 18C on cold cloudy days.
Over the 2014/2015 summer period, the house mostly stayed below 26C.
An article was recently published in Renew magazine featuring the house.
A full set of construction drawings is available for the project.