Concrete and steel are still the most commonly used materials for construction in the Netherlands. But a good house can also be made of wood and that saves a lot of CO2 emissions.

A good house is not made of wood, but of stone, the fairy tale of the three little pigs teaches. The wolf in the fairy tale blows down the wooden house with ease. It was probably not made of cross-laminated wood, also known as cross-laminated timber (CLT): thick plywood made of cross-glued softwood. The result is a panel about sixteen feet by three feet. "Enough to make large spans for floors and walls, similar to concrete," he says.

Rotterdam architect Marco Vermeulen points up to a treehouse in the middle of the Strijp-S industrial area. Visitors to the Dutch Design Week, in late October in Eindhoven, marveled at his structure: a wide staircase to a large panoramic roof, both made of wood panels. Trunks of old poplars carry the whole structure. The pavilion stands out against the gray concrete of the old Philips factories.

Building with wood is still rare in the Netherlands. Timber frame construction does happen on a small scale, but solid wood floors, walls and ceilings are unique: they can be found in only a few projects, says Vermeulen. Hotel Jakarta in Amsterdam is one such project. All walls and ceilings in the hotel are made of cross-layer wood. There are plans for a wooden residential apartment in Amsterdam, and wooden towers over a hundred meters high are to be built in Eindhoven.

At such heights, concrete and steel are more readily resorted to, for example, as the core in towers. "In principle, you can also get very high with wood, even up to a hundred meters," says Vermeulen, "but then the core of the tower becomes very thick for strength reasons." This is not dangerous, but it is expensive, also because timber construction is still rare.

A stack of screws is enough

For an all-wood building, not much is needed besides CLT. A stack of screws and possibly steel joints for the heavily loaded parts are enough. The vast majority can be attached with wood joints. "The CLT panels go into a large milling machine and come back out as puzzle pieces, with cutouts for pipes and grooves that fit together like that."

That is perhaps the greatest benefit of wooden buildings. Wood is much lighter than concrete and lends itself well to prefabrication. "Large parts of a building you can make in advance in the factory," says the architect. The rooms of Hotel Jakarta came ready-made from the factory hall. Only a few weeks after that, a building stands tall.

Such "prefab" saves a lot of time and also saves in transportation of machinery and loose materials to the construction site. Concrete can also be prefabricated, but because of its weight, it can only be done with parts of floors and walls. Vermeulen: "With wood, you can put an entire living room on the truck."

Vermeulen previously researched the potential of timber construction for the province of South Holland, the Netherlands' most densely populated region. This is because the construction industry faces a huge task: an average of 75,000 homes must be added each year in the Netherlands to meet the housing shortage. Last year 66,000 homes were blown out of the ground, but this year - with a brake on building permits due to the nitrogen crisis - the number will hover around 40,000, according to the association of project developers Neprom.

For now, those houses consist mainly of steel and concrete. Their production accounts for 17 percent of global CO2 emissions. To make steel and concrete, iron ore and limestone go through a firing furnace with temperatures above 1,000 degrees. That takes a lot of fossil energy. And the chemical fission of limestone releases a lot of carbon.

Each cubic meter of wood saves 1.1 tons of CO2

If the 1 million additional houses that the Netherlands needs until 2030 are made of wood, it will save 55 million tons of CO2, Vermeulen calculated for South Holland. By comparison, that is roughly the annual emissions of the industrial sector in the Netherlands. He bases his calculations on figures from the University of Hamburg: each cubic meter of wood replacing stone material would emit 1.1 tons less CO2.

Canadian research also reports CO2 savings in wood construction. The analysis takes in everything from raw material to processing and transportation to the construction site. As a case study, this study takes a 1,400-square-meter, five-story office building. Building this building out of wood instead of steel and concrete saves 4,000 tons of CO2 emissions.

However, the study does caution that natural gas is required in the production of adhesives for CLT panels. This proportion is disproportionate to the oil and coal consumption of steel and cement, but it is a major concern. Vermeulen: "Now, plant-based adhesives are often not used, but they can be. There is a lot of development in this area, for example bio-glue from lignin."

Glue from this wood fabric can also prevent moisture deposits and make floors and walls even more resistant. CLT may be less heavy, but it is no less strong. The strength-to-weight ratio of wood is comparable that of with steel, and even higher than that of cement. Wood can bear its own weight well. Therefore, in an earthquake test, it is found to be more resistant.

Forests now yield little

Wood construction not only saves CO2 during production and transportation, wood can also retain carbon. The carbon that a mature tree has absorbed in the trunk is not released when you turn it into CLT, Vermeulen says. About two-thirds of the carbon remains trapped in the wood; the tree roots remain in the soil.

Timber construction requires tree felling, but according to Vermeulen this does not have to lead to deforestation: "With sustainable forestry you selectively cut trees and plant back immediately, preferably with a different species. This preserves the forest and also improves biodiversity in Dutch forests. After all, that is now very limited."

With homegrown wood not covered by protected nature, he says, we could build 22,000 single-family homes a year. Wood from these forests is now mainly used for paper, biomass and matchsticks.

A shame, the architect believes, especially when it comes to biomass, as it actually releases CO2. Vermeulen would rather see more wood going into construction: "The forests now yield very little. If you turn them into construction material, you create more value." Either way, more wood is needed to meet housing demand, he says, for example by planting more forest or importing wood.

Almost everything poured into concrete without a second thought

Coen van Rooyen, director of the association of building contractors NVB Bouw, does not want to dismiss concrete just yet: "Wood is less flexible and can hold less weight than concrete." For high-rise buildings, therefore, heavy concrete is often the logical choice. To provide the same resistance to strong winds would require more wood, and that is pricey. But, "For CO2 reduction, wood is top notch and I'm a fan."

Switching completely to wood now is unwise, says Van Rooyen. "The capacity to innovate on a large scale is not there now. Besides, we desperately need concrete in the current housing crisis."

Both Van Rooyen and Vermeulen see salvation in a gradual transition where wood can coexist with concrete - not an either/or, but and/and. Vermeulen: "Almost everything is now poured into concrete without a second thought. We need to apply materials more consciously and use them where they are best."

See also the link To the article from Daily newspaper Trouw.