Stockholm Wood City sounds a little weird, but a Swedish company is planning to build a complete city made out of cheap, green, fireproof timber.
Obviously, the idea of building wooden houses, and even slightly larger structures, has been around for a very long time. However, the idea of building an entire city of wood is something new.
There is currently a global race to build the highest wooden skyscraper; the record was held for a long time by an 85-meter tower in Norway. That was eclipsed by an 87-meter tower in Wisconsin in 2022, but a new one in Switzerland will be 100 meters tall, but building an entire city is quite a different challenge.
In an area just south of Stockholm, the wooden city project will start construction in 2025. It will cover a 250,000 square-meter area, and take 10 years to complete. The final product will consist of 2,000 homes, 7,000 offices with a full support infrastructure of restaurants, shops and services.
The promoters have calculated that the project will reduce its carbon footprint by up to 40%, measured against similar projects constructed with concrete and steel. In addition, using wood will lock up the carbon dioxide absorbed by the trees when they are growing – Sweden has a renewable forest program that can accommodate such tree use, and that will also serve to absorb more carbon dioxide in the new tree growth as the old ones are harvested. The new wooden city will still use some concrete and steel in the foundations, but the amounts will be far smaller than in conventional construction. The buildings will also be much lighter, thus requiring less foundations.
The timber used for this new project will be “engineered” rather than using raw wood. This will allow different types, thicknesses and densities of wood to be used for different purposes within the design. It will also permit much of the structures to be constructed in a factory, instead of on-site.
Pre-fab housing has a bad reputation because, traditionally, it has been the cheapest way of producing volume housing. However, the “bad” part has often been cheap base materials rather than the process itself. The method to be employed by this new project will use much better quality materials, combined in a much more scientific way, and custom-made for its different structural strength requirements. Construction will also be much quicker, and less intrusive to the surrounding environment.
The nemesis of wooden buildings has always been fire. Historical horror stories like the Great Fire of London in 1666, and a similar one in San Francisco, still resonate today whenever wooden buildings are mentioned. More recently, the wild fires in California and other parts of the western U.S. have shown the vulnerability of wooden construction. A recent wildfire close to the town where I live in Colorado wiped out 1200 homes in less than 12 hours mainly because of high winds and the fact that the majority of home construction was wood.
The advantage of the Stockholm Wood City construction program is that the wood can be engineered to be fire-resistant. Tests so far have produced a three-hour fire-resistance rating, which is significant. The tests showed that the laminated wooden columns were difficult to burn and thus they were afforded an attractive rating. It also seems that, when building with wood, it is best to use large pieces. Historical experts have concluded that the Great Fire of London was caused, and spread, through mountains of “kindling” wood rather than large solid structures. The recent tests of samples for the Swedish project bear out this theory.
Concrete construction accounts for a large proportion of the world’s greenhouse gases, as well as needing more power to keep the buildings warm in the winter and cool in the summer. Wood, like other natural materials, is a much more flexible and efficient controller of internal temperature. The Swedish company is to be applauded for the concept of building an entire city with these advantages in mind.