A reader of this blog, Scott, brought a significant objection in comment to my last post, Paedomorphic Lessons. It’s worthy of further discussion, so I will respond more and encourage you to do the same. Here’s what he had to say, in full:
I struggle with the idea that “sustainability means durability”.
I appreciate the idea you are trying to convey, but is it true? What is the reason to advocate design life for a building that is “hundreds” of years? I’m not saying that we shouldn’t build high quality long lasting buildings, but why is this a “new house rule”?
You’ve likely run across McDonoughs cherry tree analogy ( the idea that nature often creates more than she needs, and often designs things that are NOT durable on purpose).
In Japan, where houses can be purchased more like autos, families often renovate by “starting over” … and I’ve been on more than a few renovations where the owner would have been better served by NOT working with what they had!
Lets also ask if we believe that a sustainable car is a “durable” car, or if a sustainable telephone is a durable telephone?
It seems to me that industry and technology legitimately challenge the idea that a sustainable thing must also be a durable thing.
My short paragraph explanation of the points wasn’t enough in this case, and I therefore agree that it does leave the argument unconvincing. It might have been better stated more completely: “In modern homebuilding, sustainability means durability.”
I too have been on renovation projects in which the existing building wasn’t worth improving, but those situations represent the problem, not the solution. These buildings weren’t worth saving because they were so poorly designed and built. Razing them is expedient, but it’s also ecologically harmful. It’s filling up the landfills and not realizing the potential of the energy expended to build them in the first place. As for the trend in Japan to tear down and start new, I can’t account for that. It makes no sense, especially in a country that so reveres its tradition of craftsmanship and building quality. Some of the oldest wooden buildings on the earth are in Japan.
McDonough’s cherry tree analogy points to the natural abundance of nature. If we could imitate the way in which nature restores itself in an endless cycle of renewal, there would be no shortages and no waste and we’d live in a much better world. While I’m a fan of McDonough’s philosophy, I’m not a fan of his apparent inability to see that there remains a distance between the ideal offered in the lessons from the natural world and the current state of our processes, habits and cultural expectations. Talking about it doesn’t get us there, and all of the attempts (including McDonough’s) to achieve real “cradle to cradle” constructions have fallen short. It’s an excellent goal and the right path, but we can’t base any assumptions on having achieved, in our human-directed manifestations, the miracle we take for granted in a simple tree.
But to take the cherry tree analogy more literally, in construction, the closer you get to nature, the more durability gets decoupled from sustainability. A cloth tent need not be terribly durable to be sustainable, for instance. Cabins made of logs and boards would need to be more durable because of the resource use, but 40 or 50 years might be a sufficient goal for a simple building made of locally available, natural materials.
The durability calculation changes, however, as the construction becomes more robust, thereby using more materials and consuming larger amounts of energy in its creation. The more we expect from a construction, the more it takes to create it, and the longer it needs to last to justify its proportionate consumption of material and energy inputs.
If we built a bridge over a river and it was made with only a couple of logs and some planks, we would be well aware that it would serve some limited pedestrian and light-load purposes only. We’d also know it wouldn’t last very long and could be replaced quite easily. This is the bridge version of using a tent for a home, which many people do throughout the world. But if we built a bridge for four lanes of heavy vehicular traffic, it would likely consume very large quantities of concrete and steel, and it would require a complex construction process to put it all in place. To be sustainable, this bridge would need to last a very long time. This is a bridge version of the contemporary American home.
As we are now trying to make homes better in many respects, they also must last even longer. Hurricane and earthquake resistant homes have more structure and better foundations. High performance homes have thicker walls and roofs, with more insulation. The imperative for improving building performance comes with an imperative to equally improve building durability to amortize its increased embodied energy. As in my example of a bridge, the sustainability/durability ratio is related to our expectations. The average American home (not to mention the better ones we should be building) is expected to be a thermal cocoon, a theater, a restaurant, a lounge, an internet café and a spa. It’s a lot different than a tent and not even close to being like a naturally eco-friendly cherry tree.
These are reasons why the life expectancy of the modern house, and the components used in its construction, can and should be measured in centuries.