Downtown woodsy
Research shows the CREE LifeCycleTower (LCT) system requires 50 percent shorter construction times and 39 percent fewer resources over the life of a building. The LCT system can also substantially reduce the amount of concrete used in construction, resulting in a lighter structure, with a smaller foundation and up to 90 percent lower CO2 emissions.[1] While the LCT ONE in Austria is eight stories, research shows the CREE building system has the ability to support as many as 30 stories.
The CREE LCT system works by building wall and floor components from glulam posts and beams.The floors slabs are a hybrid of timber and concrete, optimizing the benefits of both to meet all the structural, fire and acoustic requirements. CREE manufactures the wall and floor components off-site, under a controlled environment, where wasteful and costly mistakes can be contained and do not slow down on-site construction.
Meanwhile, on site, the foundation of a building is laid and the stiffening core is erected. The core contains the elevators and stairs and provides interior support for the hybrid wood/concrete floors. While wood is the optimal choice as a material for the core, concrete and steel can also be used. Since the components are prefabricated off site, the shell construction can go up as quickly as a story a day once the foundation and core are complete (time lapse video).
During fire, steel buildings can collapse without warning once high temperatures are reached. Conversely, wood burns predictably at a constant rate of approximately 1.5 inches per hour.
Comments
I am a big fan or sustainable design and new innovations. To state the obvious, though, my understanding of current fire codes for highrise buildings is that columns include 3 hrs of fire protection, and beams and slabs include 2 hrs of fire protection. These numbers are not based upon how long it takes the fire fighters to get to the fire. It is based upon all other systems failing and all combustable materials "burning out" of the building so nothing is left to burn.
How can a highrise wood structure achieve this comparable level of safety?
It is great to innovate, but loose the "spin" and be real about the life safety issues of a 30 story building made of wood. When a comparable level of life safety due to fire can be quantified, I'm all ears.
The concept of using wood construction to store carbon and cutting down old growth as quickly as possible to replace with young trees as a good policy to reduce CO2 levels in the atmosphere is based on an incomplete understanding of how forests function. It is the kind of claim based on a mechanistic/reductionist view of the biosphere that is promulgated by the timber industry in order to get it's hands on the last old growth timber out there.
Forests are much more than the sum of their parts. Dead standing and downed old growth trees provide both habitat for the creatures that make their homes there as well as fertilizer for the next generation of plants and trees. Large dead logs also are act as water retaining reservoirs during dry seasons. Intact old growth forests protect water quality and reduce flooding. These are only a few of the functions of intact forests. The author proposes a silvicultural policy that would eliminate these important functions of intact mature forests. It's a little like suggesting that we bulldoze subdivisions and store them in a large container to keep the carbon out of the atmosphere permanently. Never mind the impact to those that live there.
Also ignored is the carbon returned to the atmosphere from logging, milling, marketing, construction and waste. All of these activities add carbon to the atmosphere.To make any intelligent comparison of a net atmospheric CO2 reduction between intensively managed short rotation silviculture and a natural old growth forest left to decompose and regrow without management must include accounting of all the carbon involved in these two scenarios.
While the article is important in pointing out that wood can be renewable resource and is potentially a more sustainable building material than steel and concrete it strays into an area of science that is clearly outside the authors purview and makes unsupported claims about the best way to manage forests for reducing CO2 in the atmosphere. the author should stick to his/her area of expertise and avoid passing off opinion as science.
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