Traditionally a limiting factor with wood has been the building height. Historical buildings made of wood were up to 50m high, in the case of some Norwegian Stave churches, but more recently wood structures have been limited to only a few stories tall. But expanding cities need much taller buildings. Hence why this limiting of wood to low lying buildings might be about to change, as there are several proposals for skyscrapers made of wood.
Vienna‘s proposed HoHo project will be 24 stories and 84 metre’s high. A 34 story structure is also proposed in Stockholm. In Chicago, the “Big Wood” concept is for a 30 stories high apartment complex. In Vancouver another 30 floor structure is proposed. This is based on research conducted by the Architect Michael Green (see his paper on wooden skyscrapers here (note this is a 31MB 240 page document)).
And there are proposals for buildings even tall still. A concept unveiled for London talks of a 300m and 80 floor tower to form part of the Barbican complex. And in Japan, a 339m, 72 story building made largely of wood is proposed. Note that these buildings would involve a mix of wood, steel and concrete, although wood will make up the bulk of the structure.
So, what are the advantages of wood? Well, assuming its sourced sustainably (not from an old growth rainforest!), its environment impact is significantly lower than concrete or steel. Indeed, potentially wood can have a negative carbon footprint (as it absorbs carbon when it grows and burning it as biomass when disposed of generates renewable energy). Many wooden buildings are these days made to order on an assembly line in flat pack form and there’s no reason why such policies couldn’t be extended to much taller buildings. Making the flat pack wooden skyscraper a realistic future vision.
Wood is also much lighter than steel or concrete, hence the value of its use in the two ultra tall structures mentioned above (while such ultra-tall buildings are beyond the structural strength of wood alone, making as much as possible from wood lowers the weight and thus mean the concrete/steel support pillars can be smaller).
Finally, wooden structures tend to be easier to insulate, as there’s often large voids in the wall (full height glassing is also easier to implement given the low weight of the structure). This is one of the reasons wooden buildings are so popular in Scandinavia, as they can be easily packed with large amounts of insulation (they are also easier to assemble in the short few months you have in summer to put up a building before the winter snows hit). This is important because historically it has been the heating and cooling of buildings that represents the bulk of a building’s lifetime environmental impact.
But what’s the downsides? Well for starters wood need to be protected from root. That means keeping the building water tight and well maintained. The use of preservers or varnish can help, but care must be taken as some of these can have a negative environmental impact when the material is disposed off (my dad once got a load of old railway sleepers and decided he’d use them for firewood….not a good idea given the preservers they’d been treated with!). Also varnish can make for tricky conditions if it gets wet (another anecdote, we varnished some decking and as a result it became an ice rink in wet weather. I once tried to take the dog out via said decking and he refused to go out that way, fearing he’d end up sliding on his bum again!).
Another issue is that of fire risk. Obviously wood is vulnerable to fire and any structure made of wood can be a bit of a tinderbox. Note that this already applies to a lot of historic buildings in Europe. The traditional Scottish tenement for example, while the walls are solid stone, often the floors and roof structure is all made of wood (this is why fire officers make a big deal about all the furniture in such buildings being flame retardant and having smoke detectors in multi occupancy dwellings, etc.). So this is a problem we know about already and with the proper building standards such issues can be dealt with.
That said, with these ultra tall buildings, there is the issue of what to do if a fire occurs on the upper floors, beyond the reach of a fireman’s ladder. This could not only prevent rescue of people, but risk the building collapsing. My guess is some sort of system of automatic fire detection and suppression would solve the problem. But naturally, this pushes up the costs. Although as the Twin Towers collapse show, the issue of fire and collapse is not a problem limited to wooden structures.
However, the fire issue does hint at what’s the major stumbling block – a lack of standards. With existing buildings there are known building codes and standards which can be followed and designed too. However this isn’t really an option yet with wooden skyscrapers. Each one of these will have to be taken on a case by case basis, which will make for a slow (and expensive) planning process. Probably with lots of objections, some valid (which can be addressed through redesign), but also some objections consisting of the usual woolly eared anti-sustainable nonsense (which slows things down while the blindingly obvious is pointed out). The planning issues faced by the tiny house movement being a case in point. Insurance of the buildings might also be an issue until the insurance firms are confident that they can treat wooden buildings the same as any other type of building (i.e. quantify the risks).
But certainly it does show, as is so often the case when it comes to sustainable design, that there are solutions. Just because we’ve always built things this way doesn’t mean we can’t change.