Carbon Calculator

The NZ Wood carbon footprint model provides a simplified carbon footprint for a range of building designs.

Instructions

This calculator will tell you how much you can reduce your CO₂ emissions by building in timber rather than steel or concrete.  An emission can be thought of as the net release of CO₂ in to the atmosphere.

1. Select a building type from the (limited) range on offer – if your building does not match the samples shown, then you will need to choose a building which you think best fits the building that you are interested in.

2. Enter floor area and select whether to build in steel or concrete (if both options are available).

3. The ‘tree’ graphic shows you how much CO₂ emission is associated with the manufacture of the building materials (for the option selected).  This emission can be thought of as a net release to of CO₂ to the atmosphere.

4. Then compare the previously chosen option with a ‘build-in-timber’ option. 

5. The larger ‘tree’ graphic now shows you how much you can reduce your CO₂ emissions by building in timber – so many tonnes ‘saved’. 

NZ Wood Carbon Footprint Model

In each of the categories listed below, a timber building with timber components is compared with an alternative design replacing timber with steel and/or concrete components.  The comparison shows that the timber buildings have a lower carbon footprint and reduced net emissions of CO₂ to the atmosphere than alternative designs which use more steel or concrete.

The carbon footprint is provided for the following alternative designs;

• Commercial multi-storey building  in timber, concrete and steel.
• Industrial warehouse / building in timber and steel
• Farm building in timber and steel.
• Health centre in timber, concrete and steel
• School gymnasium in timber, concrete and steel

The carbon footprint is calculated by employing Life Cycle Assessment (LCA) principles and methodologies applied only to the production and manufacture of the building materials and components of the above building designs (often referred to as ‘cradle to gate’ assessment).  The assessment is not a full life-cycle assessment and does not include emissions for transport from manufacturing to the building site, emissions in construction, the use and maintenance of the building over its operational life-time, nor what happens to the building and the materials at the end-of-life.

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 chemical release of any CO₂ from the source materials (often referred to as ‘embodied CO₂’).  Applying known CO₂ emission rates for various fuels and processes provide embodied CO₂ coefficients (g CO₂ /Kg) for building materials.  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).  Applying the appropriate coefficient to a known quantity of building material calculates the amount of net CO₂ emissions for that material.

The coefficients are calculated to account for the CO₂ sequestered (stored) by the growing tree and retained in the timber products.  This means that timber products have a negative CO₂ emission coefficient.  Calculating the net CO₂ emission or absorption allows for the calculation of total emissions or absorption of whole buildings or building systems.

For each building, a Quantity Surveyor has produced a list of the main building materials and components (Kgs).  A summary table of the main material categories is provided for each building, showing the quantities, and the associated net CO₂ emissions. The total net emissions for the main materials of each building is shown and divided by the floor area of the building to provide a CO₂ footprint in kilograms of CO₂ per square metre (Kg CO₂ /m²). 

A negative footprint for a building shows that the building materials provide a net removal (and potential storage over the lifetime of the building) of CO₂ from the atmosphere, more than cancelling out all CO₂ emitted in the manufacture of all the associated building materials.

Research behind the model has been conducted by the University of Canterbury.