House Materials Life Cycle Analysis

The NZ Wood TVC – Decking – makes the claim that six tonnes of carbon dioxide has been sucked out of the atmosphere by the materials in the timber deck. The six tonnes is the amount of carbon dioxide that has been absorbed by the timber used to build the 80 square metre deck.

The deck’s carbon footprint also takes into account the amount of carbon dioxide that has emitted in the production of that timber. 

The carbon footprint is calculated by employing Life Cycle Assessment (LCA) principles and current methodologies applied to the production and manufacture of the building materials and components of building designs (often referred to as ‘cradle to gate’ assessment)¹.

The basis for the calculation of the 80 m² deck’s carbon footprint was a deck of 26.16 m²  which formed part of a standard house plan for which quantity surveyors calculated the cubic metre quantities of all building materials.

The total quantity of wood in the piles, bearers, joists and decking for the 26 m² deck was 2.39 m3, which weighs 1.21 tonnes or 1,210 kilograms.

Multiplying this by the CO₂ co-efficient for pine² (-1,644 grams of CO2 per kilogram) gives an embodied CO₂ figure of minus 1.99 tonnes or minus 76 kilograms of CO₂ for every square metre of deck.

For an 80 m² deck, 80 times -76 kilograms equals a figure of minus 6.08 tonnes. This minus 6.08 tonnes represents the amount of CO₂ absorbed from the atmosphere by the timber in that deck, net of the CO₂ emitted as part of routine forest maintenance, harvesting and processing.

Research behind the model has been conducted by the University of Canterbury, led by Professor Andy Buchanan from the Department of Civil Engineering. For further international information on Life Cycle Analysis and the performance of timber, view the Corrim study: http://www.corrim.org

1. The principal source of CO₂ associated with the production of building materials is the combustion of fossil fuels used, at all stages, to make those materials, together with the release of any CO₂ from the source materials (often referred to as ‘embodied CO₂’).  Applying known CO₂ emission rates for various fuels and processes provides embodied CO₂ coefficients (g CO₂ /Kg) for building materials.

2. This model uses the data from a NZ-specific study, updated in 2003 (Alcorn, A., 2003. Embodied Energy and CO₂ coefficients for NZ building materials.  Centre for Building Performance Research, Victoria University of Wellington).