Biodegradable Building: A Zero-Waste Medium Density Housing Design For New Zealand

New Zealand has a serious construction and demolition(C&D) waste issue. A Ministry for the Environment studyfrom 2019 found that 2.9 million tonnes of C&D waste aredisposed of at C&D fills nationwide every year (Ministry forthe Environment, 2019). Averaged across the populationthis equates to nearly 600 kg per person. AucklandCouncil’s ‘Low Carbon Auckland’ plan presents totallandfill waste reduction targets of 30% by 2020, 60% by2030, and ‘zero waste’ by 2040 (Auckland Council, 2014).

To achieve this goal of zero waste, building materialsmust operate within a closed loop (Baker-Brown, 2017;McDonough & Braungart, 2002). Materials can either bea part of a closed organic loop (natural biodegradablematerials) or a closed technical loop (man-made cycleof reuse) (Baker-Brown, 2017; McDonough & Braungart,2002).

This thesis aims to achieve a zero-waste mediumdensity housing design for New Zealand that maximisesthe use of biodegradable building materials. However,it is hypothesised along with Sassi (2006) that bothbiodegradable and reusable components will be requiredto achieve zero waste. This thesis also seeks the mostsuitable biodegradable materials for New Zealand’sclimate and the optimum construction approach tosupport these materials. This research also contributestowards reducing the embodied energy and greenhousegas emissions of the New Zealand building industry.

The most suitable biodegradable materials for New Zealandwere selected based on availability and performance foundto be untreated timber, clay plaster and, straw and woolinsulation. In-situ construction, prefabricated wall panelsand, standardised block modules were then compared tofind the most suitable construction approach to supportthese materials and was found to be prefabricated wallpanels. A building design was then pursued driven by theneed to protect the biodegradable insulation materialsfrom moisture infiltration. The design is then integratedwithin a site in Upper Hutt to address the demand forhousing densification and demonstrate the potential forapplication of biodegradable materials to an urban settingat the scale of a medium density housing development.

A detailed BIM model of the building design was producedfrom which volumes of individual components wereextracted and categorised regarding their biodegradabilityor reusability or lack thereof. This was done to determinethe proportion and quantity of biodegradable materials andwaste generated by the design. An identical design usingconventional New Zealand materials and constructiontechniques was also produced for comparison.

Biodegradable materials made up 82% of the final designconstruction by volume and 91% of the construction byvolume was diverted from landfill (reusable componentsmade up 9% of the construction). This suggests thatAuckland Council’s goal of 60% waste reduction by 2030 istheoretically possible for developments of a similar scaleto the final design. However, the goal of ‘zero waste’ by2040 seems unobtainable even if significant improvementsare made.