Radical improvements in both the nature and the economics of urban intensification are now emerging from advances deep within the realm of sustainable building design.
Usually, the features that make buildings “green” cost more, and they often need to be justified, at least in purely financial terms, by relatively long payback periods. But this time we have one that actually reduces upfront capital expenditures, significantly. At the same time, it also makes the nature of intensification less intimidating, by making five- and six-storey buildings more viable.
I’m referring to the emerging use of wooden structures for larger and taller buildings, which is gaining momentum worldwide, especially in Austria and Sweden, but also in western North America. Washington State has started permitting some taller wooden buildings; and recent changes to the building code in British Columbia have increased the permissible height of “combustible construction” for residential buildings, from four- to six-storeys.
The initial driver of this push for regulatory change has been a steadily increasing concern over the environmental sustainability of concrete and steel buildings. Energy-hogging processes used in both the extraction of minerals needed for, and the production of, concrete and steel release vast amounts of carbon into the atmosphere.
On the other hand, the cultivation and use of sustainable-harvest trees, for construction lumber, actually creates a net carbon sink, even when milling, transportation, and erection requirements are factored in. Recognition of this critical difference is increasingly being reflected in widely used sustainability ratings systems, such as Green Globes.
This important environmental advantage has led researchers to re-examine our long-held assumptions about the fire safety and structural integrity of wooden structures. In the United Kingdom, in the year 2000, one major research project involved the full-scale testing of a six-storey light-wood-frame building.
It performed so well that the UK Building Code now permits taller wooden buildings, provided they are demonstrated to provide fire-safety, and structural stability, equivalent to those constructed of concrete and steel. A nine-storey apartment building was recently completed in London, featuring a wooden structure.