The use of wood in taller buildings is big news, and now Melanie Sevcenko of the Guardian covers the story of the two towers being built in Portland and New York City. (we covered them here) There are some arguable points (plywood was not invented in Portland) and a few howlers (It is not manufactured by layering panels of 2-ft-by-6-ft lumber, that would be awfully big), but it is a good introduction for the American reader.
But the real fun is in the comments, which repeat, over and over, every misconception that there ever was about building with wood. Some get really angry AND USE UPPER CASE!!!! All of these eye-rollers have been heard before, but I thought it might be a good idea to address them all in one place. Consider it a public service; I read the comments so that you don't have to.
You can’t replace trees as fast as they are being cut down, so the argument that they will grow back is not an acceptable excuse for cutting down the forest. Do your research before you spout off about things you don’t know. Deforestation is one of THE leading contributors to climate change. PERIOD! We need MORE trees on the planet, not fewer!
The harvesting of trees in the Pacific Northwest and in Canada is not the deforestation that is contributing to climate change; that is the tropical deforestation where forests are cleared for farmland and palm oil plantations. In fact, thanks to the mountain pine beetle infestation that is killing so many trees, cutting them while still alive and turning them into CLT would be a very good thing for the climate; we should be harvesting more, not less. The wood is sustainably harvested and trees are replanted which have a net positive effect on sequestering carbon, and leads to more trees, not fewer. In fact, according to the US Department of Agriculture, "Sustainable forestry practices can increase the ability of forests to sequester atmospheric carbon while enhancing other ecosystem services, such as improved soil and water quality." Sounds like a good thing to me.
I’d be interested to see a CO2 ledger of using wood versus concrete. Burning limestone in a kiln to produce concrete obviously is environmentally destructive, but how is wood a long-term alternative?
Here you are. Note how that in every single building component, wood has a far lower carbon footprint than any of the alternatives. As for the long term, wood buildings last for hundreds of years; there are dozens of warehouses all over North America built this way. In Bologna I have seen wood that has been holding up buildings since the 13th century.
What about the gassing out of glue used to weld the plywood flats together. What goes into the glue?
Most CLT is made with one-component polyurethane adhesives which are formaldehyde free. This system was developed in Europe where they have much higher standards for health than there are in America, and where they take the precautionary principle seriously. See more on REACH and European standards in TreeHugger
However not all tall wood buildings are made with CLT; there are other technologies, like NLT or Nail-laminated timber or Brettstapel, where it is connected with wood dowels, that have no glue at all.
What about fire? It says it is fireproof. If CLT uses fireproof chemicals (as ‘fireproof mattresses’ claimed to be in the ‘70s but turned out to be toxic to breathe) will they actually make the walls, ceilings and floors toxic to breathe in? …Like the way the fire issue was skimmed over in two words…..fire death-traps!…We burnt this city. We lost our city of timber and paper. Do the hipsters know history?
Heavy timber doesn't need chemical flame retardants. It has been known for decades how wood burns, how it develops a layer of char that actually insulates and protects the wood under it. Knowing the rate at which it burns, designers add an extra sacrificial layer of wood to ensure that even after it burns and chars there is enough wood left to do the job structurally. Those hipsters may not know history but the architects do.
And as Timothy Snelson of ARUP notes, massive CLT and glulam elements are hard to get burning; "you don't start a fire with a log, you start it with bits of kindling."
What evidence is there that such buildings are healthier?
Listen to Amir Shahrokhi of sHop Architects, designer of 475 West 18th St, one of the two buildings discussed in the article. He goes on to talk about fire safety too. Wood makes for a quieter, more comfortable building and thanks to biophilia, makes us feel better. A British Columbia study found:
The presence of visual wood surfaces in a room lowered sympathetic nervous system (SNS) activation. The SNS is responsible for physiological stress responses in humans. This result opens the door to a myriad of stress-related health benefits that the presence of wood may afford in the built environment. The application of wood to promote health indoors is a new tool for practitioners of evidence-based design.
We used to build in wood and stopped!
Funny how the authors of this article, seem to turn a blind eye to the historical precedents that established very clearly, we turned away from timber for high rises, they don’t have to look to far, it’s all there staring them in the face.
There are a number of reasons that people stopped building tall buildings in wood, but one of the main ones is that it was getting harder and harder to find the big first growth timber needed after it got logged out. Now, big beams are built up out of small pieces of wood, like these glue-laminated beams in Seattle's Bullitt Center, described as the greenest building in America. (Those floors are nail laminated timber, or mill decking as it used to be called).
There were also limits in height that you could go with traditional solid wood; the engineered stuff we are using today is a lot stronger and more consistent. And we have sprinklers.
I’d like these same people to explain to us , why these days only INTERNAL windows or doors are wood, and all EXTERNAL are aluminium or even steel. …Wood is high maintenance compared to concrete, which is why it’s avoided for cladding buildings, surprised this wasn’t mentioned in the article.
Cross Laminated Timber is not approved for exterior use, so it's exposure is not an issue. Wood is used a lot for exterior cladding now, there are better treatments that keep it looking good for as long as other materials.
It would be interesting to see if CLT could become a force for renewal in economically depressed regions. Not much in terms of cost comparisons in the article. The construction industry is well aware of the near monopoly that is the global concrete suppliers.
Unfortunately, there is a near monopoly in CLT suppliers too these days, with only one plant in the States and three in Canada. However this will change as demand increases, and will be a big opportunity to put people back to work. Oregon BEST, which is investing in CLT, discusses the impact of Oregon's new DR Johnson plant:
Oregon could become the next hub for cross-laminated timber development and manufacturing due to its rich and diverse timberlands, which rank among the most productive in the world. The combination of high-quality raw materials and value-added manufacturing could revitalize small towns in Oregon’s timber country, creating jobs for sawmill workers and laminators, as well as new business for contractors, suppliers of specialized fittings and connectors and specialized equipment manufacturers.
And finally, a Three-in-one!
There is absolutely nothing wrong with steel or concrete structures. Engineered wood is actually not so great over time and very costly. There’s also a huge problem where most folk think concrete and steel as man made substances and therefore unnatural, non-organic, etc, whereas wood is obviously organic, as the thought process goes. That notion being completely absurd of course, for concrete is wholly from the Earth and quarried from limestone. Steel is nothing more than refined ore, which are essentially rocks. However, engineered wood products contain a plethora of chemicals and treatments that push the limits of human tolerance and safety.
On every effect of producing a structural material, from carbon to resource use to smog, wood comes off better than steel or concrete.
It is absurd to say that concrete is "quarried from limestone." Cement is cooked from limestone using fossil fuels, which releases a molecule of CO2 for every molecule of CaCO3. Five percent of the world's CO2 is generated in this process. Cement is then mixed with aggregate that is quarried and driven in heavy trucks to where it is mixed. Because it is so heavy, foundations have to be far bigger than with any other material.
Traditional steel production is a huge polluter and CO2 emitter.
Air emissions from steel manufacturing using the BOF may include PM (ranging from less than 15 kg/t to 30 kg/t of steel). For closed systems, emissions come from the desulfurization step between the blast furnace and the BOF; the particulate matter emissions are about 10 kg/t of steel. In the conventional process without recirculation, wastewaters, including those from cooling operations, are generated at an average rate of 80 cubic meters per metric ton (m3/t) of steel manufactured. Major pollutants present in untreated wastewaters generated from pig iron manufacture include total organic carbon typically 100–200 milligrams per liter, mg/l); total suspended solids (7,000 mg/l, 137 kg/t); dissolved solids; cyanide (15 mg/l); fluoride (1,000 mg/l); chemical oxygen demand, or COD (500 mg/l); and zinc (35 mg/l).
The overall impact of steel will be less than this because much is made from recycled steel melted in electric arc furnaces, but it is still a very different thing from wood.
And as noted earlier, engineered wood is made with formaldehyde free and solvent free adhesives and is not chemically treated. And as for the "plethora of chemicals and treatments", they do not exist except in the glue, discussed previously, and they are pretty benign compared to the plethora of fireproofing materials needed to protect steel.
You can read the rest of the comments here at the Guardian, but they are mostly repetitive.