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KNOWLEDGE

Waste - Construction and Demolition

Timber house Demolition waste can be a toxic problem...

Construction and Demolition Waste is a global problem that will continue to grow as existing aged and redundant building stock requires demolition. This is a twofold problem in that waste is produced by building demolition as well as construction waste produced in the construction of new buildings.

Disaster events reveal the problem dramatically when damaged building stock is demolished in large numbers. The Christchurch New Zealand Earthquake events of 2010/2011 required extensive areas of the city to be cleared of housing due to direct building damage and/or irreparable land damage, this was in addition to the majority of commercial and multi-floor buildings.

Demolition waste management instantly became a priority and measures were implemented that allowed for the splitting of materials into known toxic materials, recyclable metals, concrete and clean-fill and other materials including timber. Commercial structure demolition practices allowed much of this separation to be carried out on the demolition site, however demolished timber frame housing posed significant problems requiring transport to a storage facility for processing. 

While traditional timber building techniques are readily accepted by the market, promoted as a ‘green’ building material and driven by a robust industry, the question of what happens to timber housing materials at end-of-life is starkly revealed following a disaster of this type.


The above illustration shows the enormous and growing volume of material produced from housing demolition carried out after the Christchurch Earthquakes. This disaster occurred in a small city of a 350,000 population. The demolition material shown represents demolition of less than 5% of the local housing stock and less than 20% of the expected demolition volume.


While certain materials can be manually removed, the predominant material by volume is timber. The timber waste is considered contaminated, containing various toxic preservatives and other materials. Therefore it cannot be safely buried, burnt or processed as fuel as this will contaminate natural soils, aquifers and air quality. Demolition timber also contains rot, funguses and insect damage and therefore cannot be practically or economically re-used in any worthwhile manner. 


On the other hand concrete waste has proven useful in providing clean fill to greatly expand the local shipping container terminal. This expansion reclaims areas of natural harbour, with the demolition waste passing stringent environmental management requirements as a suitable material. Reinforced concrete has proven itself as an entirely recyclable material with reinforcing steel locally recycled into new steel products and crushed concrete used as both safe fill and aggregate for other new concrete and building uses.


The information, data and illustrations that disaster events produce can inform thinking of how buildings and structures are designed and built, and reveal that it is the process of Design at the front-end that can define how and where materials are sourced and how they are used in ways that can help eliminate redundant future waste.