|Prof. David R. Bohnoff|
University of Wisconsin, Madison, Biological Systems Engineering
A lot of scientific energy is going into producing new styles of construction that are more environmentally friendly. There’s something appealing about ‘new’ and ‘improved’, and a lot of great things are in fact being invented and used.
But great minds and hard work helped to make us what we are, and so it pays to look back and reconsider the tried-and-true. Professor David Bohnhoff with the University of Wisconsin-Madison is someone who is not afraid to look back to find a way to jump forward.
Bohnhoff has spent a lot of his career examining post frame construction and how those buildings can fit into the green movement. Wood, he says, has gotten a bum rap, and the competition has helped sully the science. “Wood is a superb building material from the respect of it being environmentally friendly,” Bohnhoff says.
Bohnhoff is not a big fan of rapidly renewable resources that are garnering attention in the green world, like bamboo or straw or any of the other fast growing crops being tried today. “I don’t think their use is all that sustainable compared to wood,” he says, adding: “You’ve got this great material out there – wood – if you use it properly.”
That means keeping it dry to avoid decay. And that doesn’t necessarily require revolutionary science, just plain common principals long understood by experience. “There’s always a lot of things that we’ve traditionally done knowing that they’re good practices,” he says; like using simple designs.
“Keep building shapes simple,” Bohnhoff advocates, eschewing trends towards the elaborate. “The minute we make our wall geometry more complex, our roof becomes that more complex. We end up with numerous roof planes that require different truss sizes and shapes, and these planes intersect with each other and walls added to the complexity of flashing and roof drainage systems. Also keep in mind that when you jag a wall in and then back out again instead of keeping it straight, you increase your exterior wall area … which means you’re going to lose more energy and you lose floor area … so, you have less usable space.
“More wall jags also means you’re doing more cutting and hence generating more waste on the construction site. So the rectangular shaped buildings are definitely the most environmentally friendly buildings.”
That doesn’t mean they have to be ugly. “If I had a building company out there, if I was a post frame builder, I’d be developing a lot of classic, stylish structures … we can look at our old train depots that are fairly similar in size and shape, why are some of these so incredibly attractive? Well, look at the windows, look at the overhangs, the brackets.”
Not only does overhangs help to keep water out, but it helps to extend the life of another vulnerable area: windows. “Especially in newer construction,” Bohnhoff points out in regards to the drive for airtight buildings. “Air that goes out has to be replaced; mass in, mass out,” he explains. “Today it’s going to come in through any crack it can: windows, door cracks. You can see where we might have more problems around windows than we ever had; therefore, it becomes more important to make sure the siding around the windows never gets wet, so extend out those overhangs farther. That’s something people have done historically. People have long understood the value of overhangs.”
Additionally: “Overhangs provide shade in the summer but they let the winter sun in if they’re on the south side. So they serve multiple purposes. That’s again using wood wisely.”
“What we need to do is build buildings the way we did 200 years ago,” Bohnhoff continues, noting that the less efficient the building, the more physical labor it required to maintain them. Historically, for heat, that meant cutting and carrying wood. “That wasn’t the most attractive chore, so what people did was to build smart,” he says.
Although Bohnhoff isn’t against the use of treated lumber, he urges caution because of the fickle marketplace and changing science. “There’s a lot of questions about insecticide,” he said. “The ones we use today we probably won’t be able to use tomorrow. We have a well-established history of banning certain treatments.”
Then there was the case of CCA, a wood treatment that had science behind it, but has been withdrawn from the market after the patent holders grew weary of fighting lawsuits. “CCA, it really was a very good treatment,” he said. “It’s never been shown that it’s dangerous to humans,” but the ingredients in its title (chromium, copper and arsenic) made it an easy target for litigation.
An alternative to preservative treated lumber that Bohnhoff likes is the use of concrete piers, which are more durable. And durability equates to green: “That is certainly one of the main features of it from an environmentally attractive prospective,” adding that durability is the ultimate key to green.
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