Talk about “framing” these days, and many people will think about author and linguist George Lakoff, and the post-2004-election brouhaha about how to communicate, or “frame,” political ideas.
But apparently, there’s much more obscure debate going on about another kind of framing—the kind of framing that goes into building a house.
It’s a bit arcane, really. But the crux of the debate is this: should traditional wood-framing count as a “green” building technique? Or is something else, such as steel or concrete, a more environmentally-friendly choice?
On the one hand, some folks are saying that steel and concrete have the edge: they have more recycled content, can last longer without rot or termite damage, and are easier to reuse or recycle when a house is taken down. Plus they leave forests standing, where they can absorb and store more carbon. Houses with steel or concrete framing can sometimes earn credits towards LEED “green building” certification—a fact that the concrete and steel industries are more than happy to tout.
On the other side of the debate, there’s CORRIM–the Consortium for Research on Renewable Industrial Materials—a research group loosely affiliated with the University of Washington’s College of Forest Resources.
CORRIM has completed a series of exhaustive life-cycle analyses comparing wood-framed construction with competing steel and concrete technologies. Their findings: manufacturing steel and concrete uses lots of energy—lots —and most of it comes from fossil fuels.
As a result, CORRIM finds, it’s actually more climate-friendly to cut down a forest and use it for timber, than to use concrete and steel substitutes whose manufacture relies on coal, oil or gas.
Now, I’m no expert here—I’m in no position to judge who’s right on the merits.
Still, I think there’s a fair amount of hair-splitting going on. As far as I can tell, focusing on construction materials in isolation—and to the exclusion of other impacts of owning and operating a home—is a mistake.
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CORRIM’s studies seem solidly researched. Sure, I’ve got some quibbles, like the fact that they don’t seem to account for soil carbon in their accounting—see, e.g., figure 5.2 in this pdf—even though some northwestern forest soils can store truly immense amounts of carbon—see, e.g., this study. But as a layperson, I’m really in no position to argue with their overall conclusions.
So let’s take a look at their numbers.
I combed through CORRIM’s life-cycle analyses to try to find the total difference, over 75 years, between carbon emissions for a steel-framed vs. a wood-framed home.
And when you add together all life-cycle carbon emissions—for manufacturing and transporting the materials, building the home, maintaining, heating, cooling and lighting it for 75 years, and dismantling and disposing of it at the end—the difference between the two isn’t much more than a rounding error. Take a look:
You get a similar result when you look at concrete houses in Atlanta’s climate. (I made the lighting estimate, by the way—CORRIM didn’t include that.)
When I look into CORRIM’s numbers, it’s pretty clear that the big carbon impacts from a home are from heating, cooling, and electric power consumption, which typically have little to do with the choice of framing materials. Far more important than framing are the energy-efficiency features of a house. Excellent insulation, passive heating and cooling, good daylighting, and so on can make a huge difference to long-term climate impacts—far more than the choice of a wood vs. steel frame.
And perhaps more important than any of these is the size of a house. As we’ve mentioned before, a large home built to exacting efficiency standards typically uses more energy than a smaller home that’s not up to modern standards.
Now, CORRIM may well be right about wood vs. steel—and I certainly don’t mean poo-poo a couple of percentage points’ worth of improvement. Every little bit helps.
But from what I’ve heard, some folks are starting to use CORRIM’s analyses to argue for increases in the timber harvest — perhaps on the theory that the higher harvests will make wood cheaper, which would help wood beat out steel and concrete in the construction marketplace.
To me, that makes exactly no sense. Driving down the cost of materials will, in the aggregate, tend to give homebuilders incentives to build larger homes. And larger homes will tend to use more energy than smaller ones. Sure, presuming CORRIM’s analysis is really accurate, you might save a bit of carbon by choosing wood over steel; but you’ll lose way more than that by building a bigger structure.
So we should all take CORRIM’s work for what it’s worth: a nifty way of looking at the lifecycle impacts of building and owning a home. But if you see their work used in favor of ramping up timber harvests, beware: that’s a deceptive way of framing the argument.
Matt the Engineer
I wonder what the balance would be in the Pacific Northwest. I see heavy use of wood and paper products here, presumably due to the lower cost of transporting wood products around. That lower cost for transporting wood should translate into lower emissions. Also, I believe we are further from steel manufacturers here.Another factor – although steel and concrete can have high recycled content, what does that mean compared to wood? Any non-recycled content in concrete or steel has to be dug up from the ground, whereas (sustainably farmed) trees are 100% renewable. Although not much wood is recycled around here, it is composted and there are economic incentives in place that funnel wood from demolitions out of landfills (where they decompose comparatively quickly anyway).
I’ll second what Matt said about wood being (largely) local. As oil gets more expensive, energy use will be a bigger factor. In addition, If the wood is salvage it reduces carbon dioxide emission by storing the wood for the lifetime of its use. If it comes from a thinning, it will have little impact on CO2 because the forest will close canopy within 10 years and resume the maximum possible sequestration. If the wood comes from Canada, it is more likely to be from a very large clearcut.
What about other, non-traditional, materials such as straw? I realize that, because non-traditional materials are just that and not widely in use, they wouldn’t hold a candle (perhaps not such a good metaphor to use when discussion straw houses) to the more widely used materials but it would be interesting to see a house to house comparison. Should we be looking beyond the traditional for green building materials? A quick search on line yields many examples including the following.The Strawbale House Project at Swarthmore College (1994-1998)Additional Environmental Costs and Benefits:Although far superior to traditional building methods, the house was far from perfect, environmentally speaking.. The foundation used concrete and polyethylene foam, environmentally costly substances. However, the foundation was designed to use less concrete than conventional buildings do (see Technical Details, below). There was also a small amount of concrete mixed into the stucco placed on the walls. On the positive side, our straw walls had an average insulation value of R45, which means that it took very little energy to heat or cool the house.http://www.swarthmore.edu/NatSci/es/strawbale.html
I helped build and design a building with strawbale, Stu and I wouldn’t build in Western WA (the maintenance of stucco is more intensive over here). I’d use ICF on this side and strawbale on the dry side if’n I were to build a house in this state. To Clark’s interesting point, many folk look at the CO2 emissions from concrete manufacture and re-think their postition, as do the steel-frame folk (one of my buddies in CA is a lather, and HE talks about it and mining scars). OTOH, I see clearcuts from my front porch and wonder why we can’t do a better job at harvesting. Certainly we can use the small-caliper stems that have built up from fire suppression and poor harvest practices to manufacture SIPs for building material (with SIPs you don’t necessarily need stick frames). This idea would serve a number of goals, namely: reduce fuel load in forests, get local jobs going again thru portable mills, (hopefully) depress material costs, reduce carbon footprint. ‘
Dan,Oh yeah… heh-heh-heh… I forgot about the Rainy Season. Thanks,Stu
Howdy – We’re building two “sustainable” homes now, and stewed (no ref to our prior poster) for some time on the materials question. We decided to use FSC (certified sustainably forested) lumber, avoiding engineered lumber products as much as possible. Really there’s no “sustainable” house, but this came closer than the alternatives (embodied energy and logistics did influence our decision). For other uses, like roofing, steel (or aluminum) reduce chemicals and labor needed to keep the roof moss-free, and deliver a much larger percentage of rainfall to our cisterns. And the homes will be on concrete slabs for both economic and durability reasons (chemicals for floor maintenance minimized; radiant heat retention maximized). I guess it seemed to us that there are applications where those materials are most appropriate, in spite of their downsides. We’ll be re-using concrete from the now-demolished old home as paving and patio material for the new homes, sort of making up for the new concrete or at least mitigating some of our guilt.At least that’s where we came out…
Remember steel and concrete homes have a much lower insurance rate because they have a hard time burning.
The key to reducing carbon emissions is to develop green power to produce aluminum and steel, and to keep the trees growing. Comparing future building materials using past power practices is not worthy of a university – even one that is notorious for reaching the conclusion its major donors want (e.g., Boeing, Weyerhaeuser, WDFW). Could Weyerhaeuser be playing a role here? Also, in comparing wood to anything, one needs to determine the optimum growing cycle for wood. A growing cycle of 80 years stores far more carbon than a growing cycle of 40 years.