The phrase ‘wood construction’ evokes images of nostalgia. But in 2020, it will be possible to build a modern prefabricated house, made largely from recyclable wood, surprisingly quickly. This is all thanks to Cross Laminated Timber (CLT) and robotisation, and fits in well with the principles of the circular economy. In addition, a speedy construction method is more than welcome in this time of housing shortages. But why is it that we still see very few wooden houses in our country?
Would you like to know more about circular construction or wood construction? Please contact Jan de Jong.
The open, sandy soils of the Dutch Veluwe region have something of a foreign feel to them. But that’s not how that area has always looked. Until the seventeenth century, it was a vast, sprawling forest. This changed rapidly during the Golden Age as there was a great need for wood, such as for building the ships of the VOC fleet. The felling of trees was not always accompanied by new planting. Many of the Dutch commercial forests disappeared and waste wood was often burned. There was no such concept as the ‘circular economy’ then.
Stripping, planing, sanding
Today, in the twenty-first century, the overwhelming majority of Dutch waste wood still goes up in smoke. This happens on a large scale in power stations that incinerate this kind of ‘biomass’ to generate electricity. “It’s good that wood can still generate energy in this way,” says Jan de Jong, project leader of ‘Wood in Construction’ (‘Hout in de Bouw’) at TNO’s Building Physics & Systems (BPS).
“At the moment, however, a lot of wood that is still perfectly suitable for recycling or reuse is also being lost. We’ve also noticed this during our ‘Circular Wood Field Lab’ (‘Fieldlab Circulair Hout’) project, in which we saved 300 hardwood exterior doors from the garbage container. We stripped, planed and sanded those doors. The clean hardwood that eventually remained has been given a new life, such as becoming a window frame or part of an exterior door again.”
"Carpenters were shocked by the amount of wood that was ready to be incinerated in a power station"
“During the door project, we worked closely with a carpentry mill, a door manufacturer, a laminating and finger-welding company, a building materials supplier, a waste processor and demolition companies.
I can still remember clearly how the carpenters reacted when they first visited the waste processor. They were shocked by the amount of wood that was lying there ready to be incinerated in a power station. In that huge mountain, they also saw a lot of wood that they could really use. It gave them itchy hands.”
It goes without saying that TNO is looking much further than window frames and doors. For example, the knowledge institute is calculating how much we could save in the Netherlands in terms of CO2 emissions if we were to build homes largely from wood products from now on.
“The beauty of wood is that there are multiple points in its lifecycle at which this material helps to reduce CO2 emissions. This begins as early as the planting of trees in commercial forests. From that moment on, those trees will be taking CO2 out of the air. This positive effect is not always included in the current calculations, which is actually crazy,” says De Jong.
“And if you then use the wood to build houses or other buildings, you can store the CO2 in that wood for a long time. Maybe that wood will have a second or third life after that as part of a new product. Finally, you can incinerate the waste wood as ‘biomass’ so that you can still extract energy from it.”
"As long as enough new trees are planted, wood is a construction material that will not become scarce"
“Another big advantage of wood is that there’s more than enough supply. I’m not so much talking about tropical hardwood as about coniferous wood from Scandinavian and Central European forests. For the time being, we can still build with that in abundance. As long as enough new trees are planted, wood is a construction material that will not become scarce.
What also helps is that coniferous trees grow fairly quickly and that there is still enough space for new commercial forests. By the way, it is very important when using wood in construction that the right wood is used in the right place and in the right way.”
Breaking it down chemically
“Incidentally, wood is a broad term,” emphasises De Jong. “So, we certainly shouldn’t limit ourselves to the reuse and recycling of solid wood. At TNO, we’re also looking into the possibilities for waste wood, such as the use of wood fibres to make chipboard. In addition, we’re investigating what you can do with cellulose and lignin, the substances which are left over if you break down wood chemically.”
“The new head office of Triodos Bank in Zeist is made mostly from wood”
A circular office building
Although there are already enough opportunities to use wood in housing, this is still not happening enough. And in exceptions where this does happen, it is limited to wooden frame construction. According to De Jong, this is mainly because contractors have little experience with wood and because there are definite areas of concern during construction, such as the importance of keeping CLT panels properly dry.
“Meanwhile, there are already some appealing examples of large-scale wooden constructions,” he notes. “One is the new head office of Triodos Bank in Zeist. That building is mostly made of wood. What’s more, you can take most of that building apart so that you can easily recycle or reuse all of its components. If that’s possible with such a large and complex office building, it should also be possible with relatively simple homes. Right?”