Timber in Government Buildings - Cost and Environmental Impact Analysis 2006
In June 2006 two typical government funded buildings were designed with their main structural components predominately in either of steel, timber or concrete. The two buildings were a school gymnasium, and a low-rise health building. The alternative designs were costed by a firm of Quantity Surveyors.
The timber design was the lowest initial cost in both types of building. For the gymnasium the steel design was approximately 4% more expensive and the concrete design 11% more expensive, than the timber design. For the health building the initial cost of the steel building was 7% more expensive, and the concrete design 9% more expensive, than the timber design.
When whole-life costs were added the cost differences between timber and the other designs, for the health building, reduced to 4% for the steel design and 5% for the concrete design. As far as practical each design used mainly one material for the structural system.
However, as the report notes, designers tend in practice to mix materials, based on their experience of what has been cost-effective in the past. Also, the aesthetics, "prestige", and environmental impact of the building is often of importance to the owner, and this will influence the choice of materials. So the initial and life cost of a building is often not the only factor influencing the design.
An impact assessment, using lifetime energy use as one environmental indicator, showed a difference of 2% for energy use between the health building designs, with timber the highest user. For CO2 releases the three materials in the health building were within 3% of each other with steel and timber the lowest emitters.
Due to lack of data for NZ conditions it was not possible to include other environmental impacts. However, the report notes that other environmental considerations may well influence the ranking of alternative materials. For example, concrete and steel materials may have environmental advantages in recycling.
To see the report, click on the link below.
BRANZ report June 2006 1.1MB