ccording to the International Energy Agency (IEA), buildings now produce about 31 percent of manmade greenhouse gases globally.
Progress is being made, albeit very slowly, in reducing the impact of new buildings—at least in the U.S. and parts of Europe. But we need to move faster, not just in the building industry, but across all industries, reducing our overall CO2 emissions. ...
So, how do we do so? According to the authors of Sustainable Materials: With Both Eyes Open, one answer is to turn our focus to a handful of the most polluting materials used by both industry and the building sector: steel, aluminum, cement, plastics and paper. Producing these materials—especially steel and cement—is playing a major part in pushing us past the dangerous 400 ppm CO2 “tipping point” of climate change.
The Right Roofing?
Complex variables hamper life-cycle comparison of roofing materials.
THE CHOICE OF A “GREEN” ROOF IS not as clear-cut as you might imagine. Standing seam metal roofs, for example, can last 100 years, but their emissions footprint is high on the front end, depending on the proportion of directly recycled steel in the product. The same can be said of clay tile or slate, with a lifespan in the centuries. Other contenders such as recycled rubber look viable, as do wood shingles. More “apples-to-apples” emissions analysis is needed. We expect to do a full report on this product category in a few months.
Our choice to use materials such as steel and concrete for buildings is no accident, of course. They’re strong, durable, predictable and abundant. But the latest environmental forecasts suggest that the ecological cost of continuing to produce them at current volumes, using current methods, could be disastrous for life on Earth. So what’s the fix? There’s no quick and easy answer, but we have several options, some more extreme than others. A few of the approaches past and future:
Squeeze Growth. This is probably the most controversial and contested way to reduce material use. Past efforts to limit or curtail growth have required a reversal of the dominant economic growth model in favor of a “no growth” benchmark. One major argument (and it’s a good one) is that even if the U.S. decided to attempt such a move, it’s doubtful that China, India and other expanding economic powers would agree. If the calamities of global warming become the alternative, however, extreme measures such as growth moratoriums may meet less resistance.
Optimize Design. A better option, especially for those who make their living in the building industry, is to optimize the use of both existing and future materials (e.g., more use of demolition salvage). But this solution is subject to “The Efficiency Trap,” that I’ve written about in other chapters. Environmental gains often get converted into different polluting choices—negating the CO2 avoided by the first effort. (i.e., If I can build a skyscraper with half the steel, I’ve saved enough steel and done enough environmental good to build another one.)
Hope for High-Tech Innovations. Advances in computer modeling, robotic fabrication and biotech offer tantalizing prospects for future materials that are less energy intensive, such as mushroom and other plant-based insulation, algae-powered photovoltaics and engineered plants and trees with qualities that make them ideal for specific uses. These advances are coming, but most are not commercially available yet. It’s important to take action now, during the transition period, to more benign materials and better use of existing stock.
Materials in the Modern Home
You might think that the conventionally built, wood-framed house has a relatively minor greenhouse gas (GHG) impact, because it’s framed with wood, not steel, and only uses concrete at ground level and few plastics. But when you look more closely at a home’s complete life cycle, as noted in the Univ. of Michigan study results (above), it embodies energy in surprising ways.
For example, synthetic carpet has an enormous embodied energy footprint. And although companies such as Mohawk and Interface are trying to find more sustainable materials, use of extensive carpeting is a huge polluter—in part because carpets are typically replaced every seven years or so. A typical modern carpet is made up of nylon, polyester, polypropylene or a new material called triexta. Only about 1 percent are made up of natural materials such as wool or hemp.
Reduce, then Reuse
Use of salvaged materials is resource frugal, but reducing resource use entirely is even better.
Upcycling for the Win
. The same rules of thumb that apply to the casual homeowner trying to reduce waste also apply at a global resource level. First choice should always be to use LESS, followed by re-use of materials.
Another surprise in the conventional home is the big emissions footprint of latex and paints in general. This makes more sense for the same reason that carpet is a major player. Products that require regular replacement—especially ones that are energy intensive in production—tend to spike very high over life-cycle analyses.
What about steel? Where’s the steel in a new home? You might think “appliances,” but much of the mass of steel is hidden. For example, a lot of rebar is buried inside the concrete footers and foundation.
Then there’s the big gray elephant on any building site: concrete, with its high percentage of energy intensive Portland cement, especially if it’s a conventional mix. That last point is key, because it highlights one of the many ways building professionals can greatly reduce a building’s CO2 impact. By paying close attention to the “five horsemen” materials used in a project, it’s possible to cut life-cycle emission by almost two-thirds—with little, if any, visible sacrifice for the end product.
Embodied Energy Revisited
Before we look at the pathway to those reductions, it’s important to look more closely at the idea of embodied energy versus operational energy. We’ve often talked about how a home’s initial construction may account for just 6 percent of its life-cycle impacts. Some estimates in the UK, however, put that figure closer to 16 percent. Our educated guess is that the figure is somewhere between that (around 11 percent) for U.S. homes, due to greater use of insulating plastics and PVC windows and composites.
But as a report in a British trade publication recently pointed out, a ton of CO2 released at the time a home is built is not equal to a ton released over the building’s lifespan. It’s worse. That initial CO2 may remain in the atmosphere for the life of the home, doing damage every year (full article at bit.ly/1rhengC).
In other words, says article author Kate de Selincourt, the damage is cumulative. The implication of this analysis: The choice of initial materials used in a new home may have as much impact on its greenhouse gas emissions as the lifetime performance of the building. That’s weighty information. Now what do you do with it? Change the way you build.
What Builders Can Do Now
As the researchers at Univ. of Michigan discovered, it’s possible to reduce the lifetime greenhouse gas footprint of single-family homes dramatically, by focusing on stuff that causes the most emissions. The suggestions below don’t suggest that you forsake energy efficiency for low impact materials. On the contrary, when you do use plastics, paint, concrete or steel, they should be specified carefully and with extended durability in mind. Here’s what we can safely suggest:
Remix that Concrete. The cement industry has begun to get serious about testing and monitoring the fly ash that’s now frequently used as a cement additive. Adding lightweight fly ash can reduce cement’s GHG emissions per ton drastically.
Choose Simple Slabs. A full foundation for a 2,000-sq.-ft. home will produce about 38,000 lbs. of CO2 pollution. Compare that with a slab on grade at 24,500 lbs. of CO2 emissions. Add fly ash to the mix and reduce that impact by 15 to 30 percent. The other hidden benefit of switching to a shallow foundation is that it requires less steel rebar. If you’re interested in further reducing the embodied footprint of your slabs, you could try some of the new fiberglass rebar products. Fiberglass is less energy intensive to produce than raw steel, although more research is needed to quantify the exact CO2 savings resulting from a switch to FRP. Will the product impact important concerns such as foundation cracking?
Paint by the Numbers. If you choose siding materials that require painting, longevity should be a major concern. Wood siding should be dried to recommended moisture content, never left exposed to UV, back-primed and end-coated.
Ponder PVC. Polyvinyl chloride products such as vinyl floor coverings and vinyl siding come at a high emissions cost. But are they worse, for example, than wood siding that has to be painted repeatedly? Probably—once you factor in the effect of the initial greenhouse gases over time. Although the study suggests that PVC balances out with paints in emissions over 50 years, PVC’s emissions will be cumulative, because they’re produced at the early stage. That’s lingering pollution in the atmosphere.
Consider Carpet’s Impact. Conventional synthetic carpet has a major uphill struggle to demonstrate its viability in our green future. Carpet makers need to rethink the sourcing of their materials, their poor recycling record and their role as major polluters.
Weigh Roof Shingle Impacts. Modified asphalt roofing shingles are inexpensive, ubiquitous, and their production results in significant CO2. An increase in post-consumer recycling in the past few years has reduced their overall impact. But shingles are often still treated as a disposable product. At best, they can last 50 years. At worst, under 15. When they are thrown away, unfortunately, only a small portion of the millions of tons of tear-off asphalt roofing collected each year is actually reused in paving. The paving industry reports that “1.2 million tons of reclaimed asphalt shingles (RAS) were collected in the United States during 2011 for use in new pavements.” About 11 million tons of roofing are torn off each year, so that’s about a 10 percent recycling rate. To their credit, the roofing industry has done what most carpet makers haven’t—they’ve sunk a lot of money into reducing their emissions. But they’re up against what so far have been insurmountable technical challenges in waste separation and reuse.
Think Small. With initial emissions playing a larger role, the impact of a building’s overall size should be front and center. By this standard, a smaller house is quite simply a greener house, assuming it’s built with the same mix of materials. This negates one of the few rationales for building large homes—that their performance should overshadow their initial polluting impact.
B.S. Versus Building Science
It’s tough to separate manufacturer claims from third-party research on embodied energy. As de Selincourt notes, “With so many measuring systems to choose from, everyone can show their product is ‘lower’ in embodied energy, through the careful choice of figures or—if that’s too much bother—just leaving out figures altogether.” That being said, we’ve identified for you “the big five” polluting materials. If you take nothing else away from this article, simply by changing your practices to use less of these materials, you can take part in the building industry’s part of reeling in greenhouse gas emissions. That’s today’s priority—but what about tomorrow? GB