Australia has a long history of building low density housing. At present there are just over nine million residential dwellings in Australia with 78 percent of housing stock being detached dwellings, semi-detached dwellings representing nine per cent, and flats, units and apartments accounting for 13 percent in 2014 (Australia State of the Environment, Livability: housing, 2016). However, our houses and cities are changing. Data from ABS’ Building Approvals for June 2017 report 219,284 new dwelling unit approvals were issued for 2016-17 comprising: 52.7% new houses; 15.6% semi-detached, row or terrace houses, townhouses; and 31.7% flats, units or apartments. This represents a significant change from the 173,627 building approvals issued for 1999-00 which included 71.0%, 13.5%, and 15.5%, for the respective dwelling types. The increase in ‘multi-unit’ developments represents a shift towards medium and high density living and is unprecedented in Australia’s history. This trend is set to continue and ABS data forecasts that Australia will require between 4.1 – 4.3 million new households during 2011 – 2036.
The HIA’s The Changing Composition of Australia’s New Housing Mix report notes the drivers towards medium/high density dwellings are the policy environment, consumer preferences, demography, and housing affordability. It also notes that new dwellings are covering a larger share of the lot compared with the traditional detached house and back yard. Planning policies are seeking to constrain urban sprawl by promoting infill developments in existing urban areas. The trend of people living in closer proximity is also mirrored globally. It is reported in Global Cities – The 2017 Report that in 1950, 30% of the world’s population lived in urban areas, whereas today this figure is 54% and forecast to climb to 66% by 2050. These trends demonstrate that the housing needs of our faster growing urban population are evolving and the delivery of housing solutions must embrace contemporary building technologies to keep pace.
Prefabricated housing offers many benefits for the delivery of multi-storey housing developments. Speed of asset delivery is one of the key strengths since many elements may be manufactured off-site in parallel with site preparations and footing construction. Multi-storey developments frequently have repetition in the building layout offering ‘economies of scale’ for the prefab manufacturer. The manufacture of the same sub-assemblies avoids time and cost for production line setup and sourcing different components. This repetition is not necessarily confined to floors, building envelope and internal walls, but equally includes building services that may be ‘modularised’ off-site to accelerate on-site activities and streamline project progress.
Prefabricated housing offers many benefits for the delivery of multi-storey housing developments. Speed of asset delivery is one of the key strengths since many elements may be manufactured off-site in parallel with site preparations and footing construction. Multistorey developments frequently have repetition in the building layout offering ‘economies of scale’ for the prefab manufacturer.
An excellent example of the effective use of prefabricated construction on a multi-storey residential development is the Adara Apartments (Stella B17) in Perth comprising 77 apartments over six storeys. This project included 96 prefabricated modules that were installed in 10 days. The ground floor and building cores were built via conventional methods. The collaboration included the Western Australian Department of Housing that purchased 14 units for social housing and affordable housing. A comparison of the construction methodology with a fully conventional construction approach – detailed in the Investigating the mainstreaming of building manufacture in Australia (2015) report – found prefabrication unlocked 10 – 12% cost savings with a total construction time of 11 months versus an estimated two years for a conventional methodology. A key factor in compressing the project schedule was undertaking site development and footings construction in parallel with offsite manufacture of modules which minimised site disturbance and restoration activities.
The Apartment Construction Cost Demonstration Project collaboration between Renewal South Australia and the private development sector is a demonstration project investigating design and construction methodologies to minimise building costs in a multi-storey residential development. The project is to become a case study for higher urban density and urban infill within middle ring suburbs where construction costs are considered a barrier for similar developments. In order for the four-storey development to be deemed commercially viable construction costs targeted $1800 – $2000 per square metre (GST inclusive) and a return on investment of 16% – 20%. Some of the fundamental principles adopted for the design included efficient floorplans, standardisation to mitigate risk of errors during construction, and maximising prefabrication including bathroom pods, walls and floors. Strategies to be implemented for construction included: a modular layout including a grid pattern; co-location of services; spans of around three metres; all bedrooms, kitchens and bathrooms to be a similar layout and size; and prefabrication of sub-assemblies (bathroom pods) and wall and floor elements. Of the eight different construction methodologies proposed, the preferred option was an insulated concrete form and precast concrete system. The remaining options were largely a combination of insulated concrete form and precast elements with one timber construction proposal and one brick veneer proposal. Disappointingly, panelised or volumetric prefabricated methodologies were not options which is a missed opportunity given the strong alignment between the design and construction goals and the virtues of prefab. Selection of the preferred option was also reportedly based on the cost per square metre of the development rather than a full lifecycle assessment that would capture long-term savings in operational and maintenance costs, and indirect benefits. One such indirect benefit is saved rental payments for future occupiers. A 12-month earlier occupancy amounts to $20k in saved rent based on $400 per week rental payments. A compressed project schedule also directly saves the developer interest payments on the loan which may be considerable.
Although most attention for building activity is focused on new developments, one area that is growing where prefab may contribute is the addition of storeys to existing buildings. Structurally, lightweight solutions are generally favoured since the lighter loads maximise opportunities for additional levels. In such cases prefabricated construction is an obvious choice given the accelerated timeframe for project delivery, minimal disturbance to building occupants, and lightweight systems achievable. It is reasonable to expect such opportunities will grow with the price of land.■
Dr David Heath – CAMP.H