Being constructive about building waste

This is a part of the Construction waste feature

By David Hindley - 1 February 2022, Build 188

On some construction work, just 2.5% of the materials bought for the job end up in the skip. That’s a third or less of the waste volumes produced by typical construction methods and is a clear pointer for the direction the industry must head in.

BIG BROTHER MIGHT not be watching the staff in Concision’s Rolleston factory, but it has a fierce eye on the building materials that come in the door. The firm’s commitment to designing out waste in its panellised and modular components begins with its sophisticated Cadwork design software.

Designing out waste

It takes a client’s design and requirements, considers the standard sizes the materials come in and works through various iterations to come up with the optimal order for materials with minimal waste. A bill of materials with all the sizes and details provided is then produced.

That high-tech approach continues in the factory. Computers control the saws, and there is a hierarchy of control for off-cuts, supported by the software. Off-cuts that may be used for another project are recorded and kept in numbered racks close to where they will be needed. Is a 400 mm length of plasterboard needed? You can find an offcut that fits the bill in bay F7. Some smaller pieces will be recycled. A minimal amount goes to landfill.

Waste is one of the key performance indicators for the company. It is carefully measured, so Concision can say that, for the building materials that enter the factory, 97.5% become part of the constructed panels and other assemblies – only 2.5% goes to waste. (The figure excludes the wrapping around the timber and other materials.)

Most sites generate too much waste

That figure of around 2% seems to be an achievable benchmark around the world. Scott Fisher, CEO of Offsite NZ, points out that, at his organisations’s virtual conference, it heard from Dave Sheridan from Ilke Homes UK – which builds 1,000 homes per year – that his UK business has less than 2% waste.

It is a small fraction of the amount of waste produced on most building sites. Numerous surveys and research projects have reached the same conclusion – construction of a typical new house in Aotearoa New Zealand generates an average 4 tonnes of waste.

Construction and demolition waste makes up a third to a half of all waste going to landfills and cleanfills – more than twice the amount coming from all 1.8 million New Zealand households. Auckland alone produces more than half a million tonnes of construction and demolition waste per year. This waste has another side gaining a much higher profile now – landfills are estimated to contribute 4% of New Zealand’s total greenhouse gas emissions.

Moves to help solve the housing crisis could make the waste problem worse on construction sites if it isn’t carefully addressed.

The Environmental Solutions Research Centre, founded at Unitec in 2019 to support industry-engaged research around waste and pollution, has estimated that the incoming housing densification rules could generate up to 4,000 tonnes of additional plastic waste each year, for example. See Cutting construction plastic waste more details on the work of Unitec’s Environmental Solutions Research Centre.

Cutting out waste is a positive thing

To be fair, traditional on-site building work has disadvantages that off-site construction such as that in the Concision factory doesn’t – builders might struggle taking a load of off-cuts from one job to the next. The rain and mud on many construction sites also means that materials stored incorrectly and moved multiple times can be damaged and end up in such a poor state that they can’t be installed and must be replaced, adding to the problem.

David Scobie, Business Development Manager for Concision, says the Rolleston plant is much more like a manufacturing factory than a building site. One example is the cleanliness. ‘Having a very clean factory instils the right mindset in staff.’ Where dropped screws on a building site may be swept up at the end of the day and dropped in the skip, that doesn’t happen with off-site manufacturing.

‘The whole mindset is different. If the companies that build cars built them the way most houses in New Zealand are constructed, they would be out of business very quickly.

‘For us, cutting out waste is a positive thing. It is good for us and our customers. Reducing waste increases profit.’ (Figures published by Auckland Council suggest that the average cost of materials sent to landfill from a house construction is more than $31,000.)

‘There are other benefits too – it is easier for our clients to get a Homestar rating, for example. We don’t see the need for waste reduction as a nasty thing being imposed on us.’

Lift in waste disposal levy

One thing that was imposed to try to reduce waste was the waste disposal levy of $10 per tonne (excluding GST) that applied for over a decade on all waste sent to municipal landfills. It had little impact on construction – significant quantities of waste from construction and demolition don’t go to municipal landfills and were never subject to the levy. While recovery and recycling of building materials have been growing steadily in other countries, in New Zealand, waste sent to landfills and cleanfills has been increasing.

In July 2021, the government began lifting the levy and expanding its cover. The levy for municipal landfills will be increased in stages until it reaches $60 per tonne in July 2024.

The levy scheme is expanding to cover additional landfill types, including construction and demolition fills. Construction and demolition fill (class 2) will attract a levy of $20 per tonne from July 2022, rising to $30 per tonne by July 2024. Managed or controlled fill facilities – class 3 and 4 – will see a levy of $10 per tonne from July 2023.

Take action to reduce site waste

There are a host of ways to reduce waste in construction:

Design out waste at the earliest stages of planning a building, as Concision does. Of the 5 Rs – reduce, reuse, recycle, recover and residual disposal – reducing material to only what is needed is by far the most important. Other options are often much more limited. There are few opportunities for recycling small off-cuts of treated or engineered timber, for example. Nor can they be recovered to fuel solid fuel burners.
Give clients options for different waste management approaches and let them be involved in the approach taken.
Work with waste recovery companies. Some assist with sorting materials away from the building site. Green Gorilla in Auckland diverts over 75,000 tonnes of waste per annum away from the city’s landfills each year. All Heart NZ upcycles and repurposes items that cannot easily be reused, like plastic, MDF and construction waste. There are also smaller players such as Xtreme Zero Waste in Raglan. Make sure every building site has a waste minimisation plan and separates waste by type, maximising opportunities for reuse/recycling – one recent study found that only 28% of waste from construction sites is recovered.
Talk to suppliers about reducing waste from packaging. Some suppliers now offer reusable tarpaulins rather than plastic covers, for example.
Talk about minimising waste with staff and subbies at toolbox talks.

Reducing demolition waste

A growing number of companies are taking a different approach to demolition – rather than pulling things down as quickly as possible and sending everything to landfill, they focus on deconstruction and salvage. Auckland-based TROW Group salvages more than 90% of materials from its deconstruction work.

Christchurch company Taggart, the first company to achieve the Environmental Choice New Zealand ecolabel for construction and demolition waste management, has shown it is possible to divert 70% to almost 100% of waste from landfill.

BRANZ has resources to help reduce construction and demolition waste, including: