Preliminary materials flow analysis for Aotearoa New Zealand’s building construction sector
Authors: Nelson Jacob Martin Bruton , Elliot Grace , Pickering Kim L. , Beg Mohammad Dalour 
Published: October 2022

This report describes the methodology used to produce a database of construction material flow in Aotearoa New Zealand and summarises the contents of that database. The database was produced as part of a wider research programme, Āmiomio Aotearoa, which aims to help New Zealand transition to a circular economy. In order to assess the materials flowing through the building construction sector, the research focussed on residential dwellings, which constituted a larger proportion of the sector than commercial construction in terms of number of new buildings, floor area of new buildings, and the value of new buildings.¹ The building envelope, including the foundations, structure, cladding, roofing, insulation, and lining of the structure, was examined as it accounted for the largest portion of materials in each dwelling. The data was assessed through the four key stages of material flow: material input, construction, demolition and material output. In terms of material input, timber was the most thoroughly documented material used in construction. An estimated 1.98 million tonnes of timber and timber-based products were supplied to the New Zealand market through local production and imports in 2021. Furthermore, it was estimated that roughly 10.4 million tonnes of ready-mix concrete were used in 2021. Meanwhile, approximately 850 thousand tonnes of steel are consumed within New Zealand annually. However, the amount of concrete and steel that is consumed in the building construction sector specifically is unknown. An estimation of the materials used in the envelope of residential buildings, based on consent data, New Zealand building reports and standard residential building designs, suggested that concrete and masonry were the most used materials in construction, followed by timber, plasterboard, and metals. In total, it was estimated that 2.07 million tonnes of material were consumed in 2021 in the residential construction sector. A case study using purchase order data validated this estimation, showing that the key materials studied were all of the same magnitude. Data on the number of demolitions in New Zealand was very limited, largely because consents are not required for the demolition of houses under three stories.² However, using some assumptions around census and new building consent data, it was calculated that roughly 5,488 residential demolitions occur annually in the current state of the industry. Waste from the building construction sector was studied in terms of the whole construction and demolition sector, as well as the expected waste from residential construction and demolition. It was expected that the total construction and demolition sector produces roughly 3.6 million tonnes of waste annually, with an additional 1.4 million tonnes of material from construction being recovered. However, the study found that the differentiation between infrastructure, commercial, and residential construction waste was largely unmeasured. The residential construction sector was estimated to produce 347 thousand tonnes of waste in 2021, of which 267 thousand tonnes was expected to go to landfill. This waste was produced from: The building envelope (147 thousand tonnes); the rest of the construction (49 thousand tonnes); alterations of residential buildings (25 thousand tonnes); and demolition of residential structures (126 thousand tonnes). Estimations indicated that concrete was the largest contributor to waste, followed by plasterboard and then timber. The report also includes comments from industry experts to further portray the picture of the current state of material flow in the construction and demolition sector, and the issues faced with the production of waste. Overall, this report is a first attempt to provide a picture of materials flowing through New Zealand’s building construction sector. Due to limitations of data currently being collected within NZ and available to the team within the timeframe of the project, the report has focused on estimating the materials used in the shell of residential buildings; detailing where and how materials are being recycled was out of scope. Contradiction with perceived state of the art recycling is likely due, at least in part, to assumptions that because materials can be recycled, they are indeed being recycled (as per our domestic recycle bins). Despite the data limitations, this report and associated database usefully indicate prime waste materials for incorporation into novel building materials and therefore provide insight to support the direction of future research. The report and associated database also provide a foundation which could be used to support further enterprise to provide a clearer picture of materials flows within the building construction sector.