Building tall with wood
AFor more than a century, tall buildings have been made of steel and concrete. Yet a growing number of architects are turning to a material humans have used for millennia: wood. The change has been made possible by engineered timber products such as cross-laminated timber, in which layers of wooden boards are glued together at right angles. The resulting panels are strong enough to form the walls and floors of buildings over twenty storeys high.
BSupporters point to the environmental benefits. Producing cement and steel is responsible for a significant share of global carbon emissions, whereas trees absorb carbon as they grow and store it for as long as the wood remains in use. Timber panels are also cut to size in factories and assembled on site, which can reduce construction time by a third and cut the number of lorry journeys to city-centre sites.
CThe most common objection is fire. Surprisingly, large timber elements can perform well: when exposed to flames, the outer layer chars, forming an insulating crust that slows the burning of the wood inside. Nevertheless, building regulations in many countries still limit the height of wooden structures, and insurers remain cautious. Engineers must also manage moisture, since wood that stays wet can rot, and sound, since lightweight floors can transmit footsteps to the rooms below.
DThe environmental argument depends heavily on where the wood comes from. If forests are cleared faster than they regrow, the carbon savings disappear. Advocates of timber construction therefore insist on certified, sustainably managed sources, and some researchers have called for a national limit on the proportion of harvested wood used in building until forest stocks are better understood.