Innovations put wood at the centre of progress in construction

The current awareness across society of the dangers posed by the potential for runaway climate change has had a profound impact on the value countries now place on sustainable resources. Forestry is a huge net gainer from this move. The value of wood as a resource is being enhanced by a seemingly endless series of innovations and breakthroughs, all designed to enable wood to be the prime material for environmentally friendly construction.

Stuart Goodall, chief executive of Confor, the not-for-profit membership body for sustainable forestry and wood-using businesses, points out that the technological innovation begins right from the felling stage, where the felling machinery, which also strips the branches off the trees and can debark as well, is a world away from a man with an axe or the twoman saw of old.

The saw mills too, have been dramatically transformed by technology, and Scotland’s mills are among the most advanced anywhere. “The basic problem is that you have a cylindrical log and you want to get as much square edged timber “slices” out of that log as is mathematically possible. Today, that problem is solved with 3D scanning machinery that scans every log and sends the optimum cut pattern through to the series of cutting machines,” he comments.

Actually cutting the log is no mean feat since the system has to adjust how the log is presented to the saws and work out how to marry the scan with the practicalities of making the cuts. “The more square edged timber you can get out of the log the better the profit for the mill. You make all your money on the sawn timber, which has a value significantly greater than the price you pay for the felled log. The co-product, which goes to panel board or biomass fuelling processes, is worth less than the log, though it still has a value,” he comments.

Also, if the wood is going into construction, the builder needs to know that it is structurally strong. Further scanning examines the grain and reports on the wood’s structural strength, which is then graded and marked. Wood going into fencing needs to be treated, so that is a further value add process.

“For the build environment you have to deal with the fact that when a log is first cut in the forest, it is around 50% water. As it dries the wood can twist. So wood for house building is kiln dried to take the moisture content down to say, 18%. Then it is planed smooth and the edges are rounded slightly to make it easier to handle. All this is value add from the mill,” Goodall comments.

A new saw mill today requires an investment of around £30 million or so. “If you are an inward investor, you need to find the right site, preferably within a 50 or 60 mile drive of a steady source of supply. It is a feature of the saw mill market in the UK that it is predominantly family owned,” he notes.

There is a growing number of wood-derived or woodbased products currently either new to market or being lab tested but two technologies that are now very much part of the construction industry’s armoury are crosslaminated timber (CLT) and glulam wooded beams. CTL was a Swiss invention in the 1990s and involves creating structurally strong plywood by alternating the grain pattern on panels and gluing them together. Multi-story structures using CLT can be built in half the time of equivalent concrete and steel structures, and have a much lower carbon footprint.

For those worried about fire in multi-story wooden constructed structures, surprisingly, they perform well in fire tests because of the char layer that forms on the surface and protects the integrity of the load bearing wood underneath. Because wood is flexible, it also performs much better in earthquake simulations, than equivalent steel and concrete or brick structures.

Glulam is a rather different technology. It is made by gluing laminates of solid timber together under pressure and heat. The laminates need to have been accurately planed and can be designed as curved as well as long beams. They are ideal for sports halls, swimming pools and other public buildings where the architect or designer wants to avoid having to use supporting pillars other than on the periphery of the structure. Glulam beams can be a lot longer than the single pieces of timber that could be obtained from a single log and have much greater strength. It is not, in itself, a new technology, having a pedigree dating back over a century but new adhesives technologies, resins and epoxies have added strength and durability. Glulam beams are increasingly being used in combination with CLT to create large scale, prefabricated units.