by aleida, on October 28th, 2009
Image courtesy of Michael Schönitzer via Wikimedia Commons
Have you ever thought about the word “renewable”? It’s become rather ubiquitous lately, particularly when applied to energy sources. Wind, solar, hydro, and geothermal are rock stars in the renewable energy line-up on the basis that there will always be wind, sunlight, waves, and raging heat at the core of planet Earth.
The word “renewable” has also gained a strong foothold in material selection, where products made from so-called “rapidly renewable” materials (chief among them bamboo and cork) have become favored, and rightly so, by specifiers. We ourselves have eagerly embraced these products.
But then I wrote the post on mesquite tiles. In writing it, I referred to mesquite as a rapidly renewable resource, with trees ready for harvesting at around 40-60 years of age. That age range left me with a rather strange feeling. It didn’t feel entirely correct to brand as rapidly renewable something that, had it been planted when my parents were born, could still need a few more years on the ground. Even if mesquite were cut down after only 40 years, that’s still a long time. A lot can happen in 40 years.
This got me thinking: what exactly do we mean when we speak of a “rapidly renewable” material? Or even just a “renewable” product? The meaning cannot possibly be the same as when we speak of energy sources. I have been unable to identify a material currently billed as “rapidly renewable” that is renewable in a matter of seconds – like the energy in ocean waves. The available “rapidly renewable” building products all contain materials that belong to the Plantae kingdom (you know, the five kingdoms: Animalia, Plantae, Fungi, Protista, Monera). In thinking about a rapidly renewable plant, we must think of it in terms of its biological maturity, i.e. the time it takes for the plant to be ready for harvesting.
We recognize that some building products contain plant life that grows really, really fast. Kirei Board, for example, is manufactured using reclaimed sorghum straw. Sorghum reaches biological maturity within 3 – 4 months. Waste from wheat harvests is reclaimed into building products. Wheat reaches biological maturity at 110 – 130 days (4 months, give or take). Same goes for flax, whose straw has been incorporated into flooring products. Sunflower seeds mature in about 3 months, and their hulls have been used to manufacture durable surfaces. Coconut shells, used in wall finishes, can be had as often as once a month if you have a healthy palm tree. Bamboo, despite the fact that some stalks can grow up to 4 feet within a 24-hour period at the peak of development, does not actually reach biological maturity in one day. Depending on the species, the climate, etc., it can take at least a couple of years for it to be ready to harvest. Cork, when harvested correctly, can be stripped off a tree only once every 9 years, but only after the tree is already more than 20 years old. For most hard woods, biological maturity isn’t reached until a century later. White oak, for example, is best if harvested at around 80 – 120 years of age.
Considering these large discrepancies in biological maturity, it doesn’t make complete sense to speak about bamboo, mesquite, and flax straw as all being “rapidly” renewable.
After some back and forth in the office, here’s how we define rapidly renewable: a resource that can replenish itself within a human generation. On average, a generation (in cultural terms, not familial) lasts for about 16 years. The Baby Boom Generation is commonly identified as lasting from 1946 – 1964, an 18-year period. We’ll be a little more generous, and say that a generation is a 20-year period. To us, this means that whatever we need now and cut down, can be ready for harvesting when the next generation needs it.
Anything that needs more than 20 years to reach biological maturity becomes, for us, simply renewable, and includes basically all of the hard woods. Yes, even mesquite, which hereby officially loses its rapidly renewable status in our materials library.
But we feel we must have another category to bring attention to all those materials which mature fast, even by a human life-span. Thus we have…hyper renewable: a resource that replenishes its supply within a five-year period. All the reclaimed crop waste fits into this category, and even some bamboo species.
It will be fun to walk the Greenbuild expo floor (in just two weeks!) with this framework in mind. I’ll be especially interested in finding hyper renewable materials because they are very innovate. They are effecting an actual paradigm shift by looking at what is typically considered waste and up-cycling it, turning it into a technological nutrient that can help us move away from business as usual.
Do you know of any hyper renewable products? As always, if you do, let us know!
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[...] defining “rapidly renewable” [...]