According to research by the Commonwealth Scientific and Industrial Research Organisation (CSIRO), “energy use in buildings is responsible for 26 per cent of Australia’s greenhouse gas emissions and is the primary cause of peak energy demand on the electricity network.”
Furthermore, on particularly hot days, air conditioners in Australia can consume as much as 22 per cent of all the electricity generated across the nation.
Australia is one of the worlds’ most urbanised nations, with 89 per cent of residents living in cities. The stringent Passive House standard, though not yet much of a factor in Australia, offers the potential for multi-family housing that serves the continued demand for urban housing while drastically reducing energy consumption.
Two multi-family Passive House projects in Portland, Oregon, one just completed and one just begun, are examples of innovative projects that could be adapted for Australian cities. Portland is one of the strongest Passive House markets in the US, with more than a dozen projects built already.
The Kiln Apartments were designed by GBD Architects of Portland. This recently completed infill project offers 19 one-bedroom apartments that range from about 50 to 70 square metres. The project also includes first-floor retail space. The site dimensions demanded a longer and narrower structure than is ideal for maximizing energy efficiency, so other elements had to be optimized to cut energy use by 70 to 80 per cent to meet Passive House standards.
As with all Passive House projects, the building is heavily insulated, with 100 millimetres of rigid foam insulation under the slab and footings. The walls are insulated to R-42 with dense-packed cellulose, and include two layers of 50-millimetre exterior rigid insulation. The R-70 roof uses wooden trusses with 500 millimetres of batt insulation, plus 100 millimetres of rigid foam insulation on top.
Triple-glazed metal-clad wood windows from HH Windows & Doors comprise 22 per cent of the surface area of the envelope, and are deeply inset and fitted with sunshades to minimize summer heat gain. A building-scale heat recovery ventilator supplies continuous fresh air, and solar-thermal charged radiators provide the heat.
The four-storey Kiln project is also similar to one of the most popular housing types in Australia, as reported by the Housing Industry Association. In fact, the greatest change during the CSIRO's research period has been projects of four storeys and higher.
The Passive House standard is simple but rigorously dedicated to energy efficiency. It requires (as stated at the Passive House Alliance web site):
- Maximum heating or cooling energy of 15 kWh/m2 per year.
- Maximum total source energy of 120 kWh/m2 per year. (“Source energy” by definition includes the energy required to produce and deliver the energy to the site, and can be offset with solar thermal and other measures. Photovoltaics cannot be used to offset this energy, but are recognized, at this time.)
- Maximum air leakage equivalent to 0.6 air changes per hour at 50 Pascals (ACH50), (~0.03 ACHNAT).
In addition, the following recommendations vary based on specific climate region:
- Window u-value ≤ 0.14 Btu/hr-ft2-°F (0.8 W/m2/K)
- Ventilation system with heat recovery with ≥ 75 per cent efficiency with low electric consumption @ 0.68 W/cfm/ft3 (0.45 Wh/m3)
- Thermal bridge free construction ≤ 0.006 Btu/hr-ft-°F (0.01 W/mK).
It’s generally easier to achieve these targets with larger buildings, such as multi-family buildings, than it is with single-family homes.
"Exterior surfaces are where we generally lose our heating and cooling energy," said Todd Collins, building consultant and owner of AE Building Systems in Golden, Colorado. "Because larger buildings have more volume compared to exterior surface area, meeting 15 kWh/m2/yr or 4.75 kBTU/ft2/yr is relatively easier than with a smaller building."
In Europe, more than 25,000 Passive House (Passivhaus) projects have been built, including dozens of multi-family projects and an Austrian apartment complex with 361 units. In addition, schools, hospitals, sports facilities, a supermarket, and public buildings have been built to the Passive House standard.
The Orchards at Orenco is a multi-phase affordable housing project located near the MAX Light Rail Station in Portland. When complete, the project will be the largest certified Passive House project in the US. Strategies for meeting Passive House requirements include 305-millimetre roof insulation, 250-millimetre wall insulation, triple-glazed windows, and careful site orientation.
Phase 1, now under way, will offer 57 units of affordable housing, cost about $US14.5 million and is scheduled for completion in June of 2015. The 40 one-bedroom units and 17 two-bedroom units will be available to people earning up to 50 per cent of the area’s median family income, with rents ranging from $611 to $733 per month. REACH CDC is the project developer.
Overall, 21 multi-family projects have been submitted for certification in the US. The variety of multi-family projects, as noted in this blog, shows that projects of all types can be certified to Passive House standards.