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    The cost of sustainability: Hopkins Street Affordable Housing by Xsquared Architects

    Geraldine Chua

    The Hopkins Street Affordable Housing Development, situated in the heart of Moonah, Tasmania, is a project that pushes the boundaries of sustainable living while managing to remain cost-effective in the long run.

    Designed by Xsquared Architects, the project had an initial brief by the Tasmanian Government Department of Housing and Human Services to create a purely functional development for 30 independent units. In alignment with the Federal Government’s Nation Building Economic Stimulus Plan, there was also a requirement for a 6 star NatHERS rating for all units, and the use of energy efficient lighting and hot water systems.

    It was within this brief that the architects recognised the possibility of creating a development that would set an example for public housing on the performance levels that could be achieved. Capitalising on that opportunity, they established an ambitious target that went above and beyond expectations.

    What has been achieved since by Hopkins Street is a 5 Star Green Star Multi-residential design rating, the first and to date, only such rating for the state.

    However, this outstanding result is not without its challenges. Wanting to boost the energy efficiency of a building is admirable, but often comes at a price – and sometimes, that price is higher than what can be managed.

    “The biggest challenge for us in the Hopkins Street Affordable Housing project is inherent in its title – ‘affordable housing’. We were given a brief and a budget for a ‘business-as-usual’ development from a heating and insulation perspective,” says Peter Scott, director of Xquared Architects.

    “But [we] developed an enlightened and performance-leading exemplar of public housing within this budget, which has enabled our client to pass on this benefit to the managing organisation and tenants.”

    Photography by Jonathan Wherrett

    The affordability of Hopkins Street therefore runs parallel to the design inspirations of the project, one of which is the maximisation of energy efficiency via efficient heating, hot water systems and effective insulation so that running costs are as low as possible for occupants with a limited disposable income.

    According to Scott, many tenants now pay half or a quarter of the amount of their electricity bills as compared to previous homes.

    Overall, every unit achieves an energy rating of at least 7.3 stars, with three of the apartments achieving 8.1 stars. This standard is made possible by an effective insulation strategy, whereby the suspended floors have a R2.65 100mm RMAX Isolite SL grade expanded polystyrene, and the windows and doors are the AWS Vantage 517, 541 and 548 series, fitted with clear, double glazed IGUs.

    In addition, the ceilings (including those between units) are insulated with R4.0 Pink Batts ceiling insulation, and the walls are insulated with R2.7 Pink Batts Sonobatts Silencer acoustic bulk insulation, which Scott notes is atypical.

    “It is unusual to incorporate this style of insulation for its thermal properties, but we wanted to maximise the performance of the external envelope of the building, and this relatively high density product can be accommodated within a traditional 90mm cavity, so we designed the external facades to suit its use,” he says.

    “RMAX Isolite Insulation and Vantage windows and doors were selected because they are produced locally, reducing the greenhouse gas emissions of transport, and we had used them successfully before and knew they could be tailored to suit our particular requirements without cost penalties.”

    Each unit is fitted with a single reverse cycle heat pump. Depending on the size of the flat, Mitsubishi SRK35ZIX-S, SRK50ZIX-S and SRK60ZIX-s packaged units were specified.

    Although these heat pumps are usually utilised for commercial applications, Scott says they were selected on the basis of being amongst the most energy efficient units available according to the Federal Government’s Minimum Energy Performance Standards (MEPS) energy rating database.

    The heat pump units also only use non-ozone depleting refrigerant, and are deemed to be highly reliable, so that tenants were unlikely to be left with no heating due to an appliance failure.

    When asked what his favourite product used was, Scott explains that the Vantage glazing suites not only enabled the team to fit double glazed IGUs and achieve large expanses of glazing without incurring any significant heat loss penalty, but also helped to define the openness and ‘feel’ of the development.

    The view axis is also filtered by drilled aluminium balustrades, which provide privacy and offer the reassurance of passive surveillance in accordance with crime prevention through environmental design principles.

    “We really relished the opportunity to push this design freedom to the limit, with many units able to have floor-to-ceiling and wall-to-wall glazed northern facades as a result,” says Scott.

    Scott furthermore gives special mention to the Pink Batts acoustic insulation and the Mitsubishi reverse cycle heat pump units. As standard products, they were used in innovative ways with no cost impost for the achievement of a better performing building.

    The heating and insulation products chosen for Hopkins Street Affordable Housing therefore meet the architects’ ambitious energy efficiency targets without skyrocketing the costs of construction and all future running costs.

    Photography by Ray Joyce

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