Plastic waste study offers lessons for sustainable site practice

BRANZ-funded research shows that up to 80% of plastic waste can be diverted from landfill – offering practical insights for landscapers aiming to improve onsite sustainability through better planning and material management.

The research examined 7.2T of plastic waste collected from six separate construction sites in Auckland, which was separated and categorised into 46 groups. In total, 4.5T was kept out of landfill. The best-performing site diverted about 80% of its plastic waste.

Although the study focused on building construction rather than landscaping, its findings are relevant to landscapers working on or alongside construction sites.

Many of the waste streams identified in the research are also likely to appear in site-based outdoor work, particularly packaging, plastic pipes, protective materials and polystyrene.

HIGHER RECYCLING RATES

The results suggest that plastic diversion rates of about 60% to 80% are achievable on Auckland construction sites, where suitable recycling services are available. However, the study also found that these outcomes required time, planning and active involvement from both site staff and the research team. Existing recycling infrastructure in Auckland was also a factor.

For landscapers looking to reduce waste, the clearest practical lesson is to focus first on the largest and most recyclable streams. On Auckland sites, the study identified soft plastics, plastic pipes, shrink wrap and expanded polystyrene as priority materials because they were generated in large quantities and had viable recycling options.

The timing of waste generation is also important. The study found that most plastic waste was produced during the final stages of construction. For landscapers, this points to the value of maintaining waste separation through the later stages of a job, when finishing materials, packaging and protection products may be removed or discarded.

“As most plastic waste was generated in the final stages of the project, we would recommend that sites make a particular effort for waste management and separation during this stage,” researchers said.

SORTING AND SEPARATING

One site increased its plastic diversion rate by 20% by just separating and recycling shrink wrap. That site achieved an overall plastic recycling rate of about 80%, although it was also the only project in the study to use shrink wrap in significant quantities.

The finding highlights the impact that a single high-volume material can have on waste outcomes. For site teams, separating one major plastic stream may be more effective than trying to manage every plastic type in the same way from the outset.

Across four sites, excluding two incomplete datasets, packaging accounted for 47% of plastic waste. Construction components made up 34%, while building protection and tools accounted for 15%. This gives site teams a useful starting point: reducing, reusing or separating packaging can have a significant effect on overall plastic waste.

The study also identified several problematic materials. These included backing films from adhesive weather barriers, woven plastics, cross-linked PEX pipes and composite cable reels. These materials could not be processed easily by recycling operators or were generated in relatively large amounts. Fibre cement cladding, while not a plastic product, was also identified as difficult to manage because it could not be recycled at the time of the study.

PRIOR PLANNING PREVENTS POOR PERFORMANCE

The findings suggest that waste planning should be built into the way sites are managed, rather than treated as a clean-up task at the end. Medium and large sites were advised to use waste generation data to estimate the types and volumes of waste likely to be produced at different stages of construction.

The study recorded an average total waste generation rate of 39.1kg per m² across four sites. The average plastic waste generation rate was 0.61kg per square metre. Plastic waste generation rates across all stages of construction are not well established, making the study a useful reference point for future planning.

Cost remains a consideration. On one site, waste management involving separation for reuse and recycling amounted to 0.61% of total project costs. Traditional skip disposal was calculated at 0.27% of total project costs. For that specific site, researchers reported that the site owner did not regard the higher cost of the more sustainable approach as unreasonable – which indicates some clients may be open to paying more for sustainable disposal of materials.

For landscapers, the broader message is that sustainability on site depends on practical systems. These include identifying the main plastic streams before work begins, keeping recyclable materials separate, paying particular attention to late-stage waste, and checking which materials local waste suppliers can accept.

The Auckland findings may not apply in the same way across the whole country. The study noted that, nationally, reuse and recycling options for these products need further investigation.

Even so, the research shows that substantial plastic diversion is possible where materials are separated and suitable recycling routes exist. It also shows that higher diversion rates depend on labour, planning, site discipline and access to the right services.