A small prefab home recently on display in Melbourne is Australia’s first carbon positive prefab home, according to ArchiBlox, the design-build firm that built it.
The company’s Carbon Positive 01 was on display as part of The New Joneses and the Sustainable Living Festival.
According to a company spokesperson, “Carbon positive moves beyond carbon zero by making additional ‘positive’ or ‘net export’ contributions by producing more energy on site (or through affiliated schemes), than the building requires and feeding it back to the grid.”
The home encloses 77 square metres in a simple rectangular shape on one level, with one bedroom, one bathroom, a kitchen, a dining room, and a living room.
A sunroom-type space the company calls a “conservatory” is oriented to the north and is “not only a place to buffer the external environment, but a place to grow vegies, to relax, unwind.”
The conservatory features passive solar design with abundant glass and clerestory windows to the north, and large overhangs to block the summer sun.
“The dwelling is designed big but built small with numerous household functions built within the joinery such as study desks, ironing board, ladder and sleeping lofts,” the Archiblox spokesperson said.
The space also features sliding doors to isolate the other living areas from the conservatory. Thermal mass stores and releases heat during cooler months. A green roof insulates the home and stores carbon, while the earth berm design on the southern facade also insulates the house. Cooling tubes transmit air under the floor from the cooler south side to the warmer areas of the house.
The carbon positive performance demands a systems approach through the house, with every design feature contributing to the performance of the system as a whole.
“Our carbon neutral materials are complemented by the internal vegetable gardens – watered with our recycled grey water system – and the evaporative coolers, which use a combination of natural airflow and recycled plastic bottle pockets,” the spokesperson noted.
According to the company, the house has undergone a Life Cycle Assessment (LCA) by eTool and was awarded Platinum certification. LCA calculates the building’s carbon emissions from all phases of construction, including materials’ manufacture, materials’ transport, the materials themselves, building operation, and ongoing maintenance. The home’s results are measured against a benchmark building and are summarized below:
- A savings of the equivalent of 659 kilograms of carbon dioxide per year per occupant, 116 per cent greater than a traditional dwelling
- The equivalent of 1,016 tonnes of carbon dioxide is saved over its total lifespan, equivalent to planting more than 6,000 native trees, or 135 zero energy Australian homes for one year.
As with many prefab homes, costs are competitive against homes with comparable amenities.
“Like-for-like building prices can be marginally cheaper,” for prefab homes, in the range of five to 10 per cent, Bill McCorkell, architect and company director, noted.
McCorkell added that the big factors driving interest in modular housing are not just architectural design and better quality materials, but “the control owners have over the notorious twin building variables of time and cost."
Prefab building is gaining popularity around the world. According to The Global Prefabricated Buildings Market – Key Trends and Opportunities to 2017, a report published by Timetric, the global focus on environmental issues such as energy use “has provided opportunities for the sustainable buildings market over the traditional buildings market.”
Governments around the world have begun incentivizing more efficient buildings, leading to increased demand for prefabricated buildings.
The Asia-Pacific market for prefabricated buildings is the largest worldwide at $44 billion (US), which represents 49 per cent of the $90 billion worldwide market. The European prefabricated market comes next with $31.5 billion, and the North American market with $10.2 billion.
Builders report a variety of benefits from using prefab construction.
Prefabrication and Modularization: Increasing Productivity in the Construction Industry, a report published by McGraw-Hill Construction, surveyed builders and industry professionals and notes that “prefabrication/modularization are seeing a renaissance as technologies, such as BIM, have enabled better integration of prefabricated/modular components; as changes in design such as the emergence of green have made certain advantages of prefabrication/modularization more important; and as innovative offsite techniques have emerged.”
According to the report:
- 66 per cent of respondents said prefab building shortens project schedules; 35 per cent said it does so by four weeks or more.
- 65 per cent reported that project budgets were lower; 41 per cent said they were lowered by six per cent or more.
- 77 percent of respondents reported decreased site waste; 44 per cent said it was decreased by five per cent or more.
Prefabricated buildings offer some attractive features for high-performance homes. Lower energy usage is facilitated by tighter quality control and proven designs. The designs are adaptable and can be systems of panels or modules. Additional panels or modules can be added efficiently, so the buyer can choose a design tailored to his needs and wants, without requiring custom work. Some modules/homes are nearly complete when they leave the factory, meaning some can be operational on the day they’re installed on site.
In addition, there’s evidence of increased durability. The US Federal Emergency Management Agency reported that modular housing withstood well the effects of the massive Category 5 Hurricane Andrew in 1992. FEMA reported "relatively minimal structural damage in modular housing developments. The module-to-module combination of the units appears to have provided an inherently rigid system that performed much better than conventional residential framing."