Increasing the amount of timber used in large-scale commercial buildings can decrease some environmental impacts of the building, according to a Ministry of Agricultural and Forestry study.

The research project, Environmental Impacts of Multi-Story Buildings Using Different Construction Materials, modelled the life cycle energy use and carbon dioxide (CO2) equivalent emissions of four similar office building designs that used different materials as their main structural element: concrete, steel, timber and 'timber-plus'.

The latter also used wood-based non-structural elements. Results indicated that of the four, the 'timber-plus' building had the lowest net environmental impact, producing 4571 tonnes CO2 equivalent while the steel building had the highest net impact producing 6,789 tonnes of CO2 equivalent. Timber was second lowest (5,454 tonnes), followed by concrete (6,627).

MAF Sector Performance Director Iain Cossar says the study provides valuable information on the life cycle environmental impact of various construction materials and the benefits of maximising the use of wood. "The report also fills an information gap concerning how much wood can be used in the construction and fit-out of commercial, large-scale buildings in New Zealand.

It shows that increasing the use of timber can decrease the total energy consumption and environmental impact of the building over its 60 year lifetime. "In addition, the study found that from a technical point of view, a commercial building of up-to six stories could feasibly be constructed on a timber structure, something that does not typically happen in New Zealand."

The study considered the full life cycle of the buildings including the initial embodied energy of the materials used, maintenance, transport, operational energy and end-of-life scenarios. All four buildings were designed for a 60-year lifespan and were based on the design of an actual six-storey concrete building.

The research used Life Cycle Assessments which measure the environmental impacts associated with a product, process, or activity by identifying energy and materials used and wastes released through the course of a product's life-span.

The study was led by researchers from the University of Canterbury and included work by Crown Research Institute Scion and Victoria University of Wellington. The project reports can be found on MAF's website www.maf.govt.nz/forestry/publications.