The building industry, coupled with the authorities and regulators that govern it, have finally, begrudgingly, started to accept the importance of embodied carbon. And the makers of building products have been dragged, kicking and screaming, into providing Environmental Product Declarations that tell us how much carbon was emitted in production. But what is the easiest way to get a handle on upfront carbon in the housing industry?
Treehugger recently wrote about a new, easier tool called the BEAM Estimator for calculating it, if you have a design to input. Perhaps a better place to start is the "Material Carbon Emissions Guide" prepared by Builders for Climate Action (BFCA)—the same team behind the BEAM Estimator.
This little explainer was written for Nelson, British Columbia, Canada—169 miles north of Spokane, Washington—and is based on the analysis of 34 houses in the area, which were run through the BEAM Estimator. Its purpose is straightforward: "These product rankings help facilitate low-carbon decision making by giving consumers a sense of the average amount of material carbon emissions associated with different product types."1
BFCA also stated, "It should not be seen as something that replaces a life cycle assessment. It instead seeks to offer itself as a starting point for integrating the consideration of material carbon emissions into more decision-making processes."1 But it is a very useful starting point indeed.
It also starts with those first three stages of upfront carbon: "cradle-to-gate" or the raw material supply; transport to the factory; and manufacturing. But that is the biggest chunk of upfront carbon (65% to 75%) with the most solid data. This is what BFCA calls material carbon emissions (MCE). "In other words, this guide tells you which materials have less emission-intensive raw material acquisition and manufacturing processes and therefore a smaller carbon footprint," write the authors.1
I previously expressed skepticism about the concept of MCE and thought the full upfront carbon numbers, including transportation to site and installation, should be included. But Chris Magwood of BFCA explained to Treehugger why he sticks with the basics: bad data.
"I did a deep dive for my thesis and found that the assumptions in the LCA software I was sampling were typically 50% to 150% wrong in their estimations compared to an actual analysis of how materials move around," said Magwood.
I have finally come around to the concept. This guide was done for Nelson, British Columbia, but the numbers in it apply anywhere—they are intrinsic to the material, not where you bought it or how you use it. And the story it tells will surprise a lot of people.
In the homes examined for the guide, we find they are like carbon icebergs, with the bulk of the MCE buried in the foundations and the basement. This number will obviously vary depending on where you build, how deep foundations have to go, and whether you have a basement at all.
The guide shows you can reduce the carbon footprint of concrete significantly by increasing the amount of slag and fly ash while reducing the amount of Portland cement. But it also makes a point we often stress on Treehugger: our good old radical simplicity principle.
"One of the most important things to remember when seeking to integrate the consideration and reduction of material carbon emissions is the role that building designers, engineers, and architects play. These professionals can design shapes, structures, and aesthetics that lead to less material carbon emissions. Homeowners can request or require these considerations. Reducing material carbon emissions means applying their consideration as early in the design phase as possible."
The fun begins with insulation, which makes up 15.3% of a typical house's carbon footprint. The data are presented in a typical Canadian mix of metric and American measurements, showing the kilograms of carbon dioxide equivalents per 100 square meters of insulation area at R-13, with insulation rated at R-value per inch. The diamond represents an average; sometimes there are ranges because of different products in the same category.
One can immediately see why smart builders are bailing on closed cell spray foam insulation, which was particularly loved in the renovation world; I have it in my own home. It has over three times the carbon footprint of the next biggest emitter. (There is a good article about responsible renovation contractors giving up on the stuff in Green Building Advisor.)
The other shocker is mineral wool has, on average, four times the footprint of fiberglass. For years, green builders avoided fiberglass. Then the manufacturers got rid of the formaldehyde binders and increased the recycled content, and it started looking better and better. Given that Healthy Building Network found it to be the second healthiest insulation after cork, there are good reasons to look at it again.
But then there are all the carbon negative cellulose insulations, from hemp and newspaper to wood fiber and straw—these are looking more attractive than ever. Wood fiber is new to North America but is coming next year when the TimberHP factory opens in Maine. It could be the next big green thing.
Rigid insulation boards, often used below grade or for additional insulation on the exterior, tell a different story. Extruded polystyrene (XPS) was horrible stuff until recently when it was reformulated to eliminate the hydrofluorocarbon foaming agents and rebranded as NGX. But when asked if it was back on Magwood's menu, he told Treehugger that "it's just less bad."
To make life difficult for users of the brochure, they measure rigid insulation at R-5 while they measured wall insulation at R-13. This recognizes that they are used differently, but obscures the fact that even the new improved NGX foam has 12 times the carbon footprint of fiberglass.
In Nelson, cladding is just behind insulation at 12.5% of the household emissions. There was no surprise in learning brick is terrible but acrylic stucco was surprisingly high, making it a carbon crime as well as a design crime. Most of the low-carbon cladding materials are combustible—a big problem in the West these days.
The authors of the study note this might be a price we have to pay: "Although many of these fire-resistant products have high material carbon emissions, in certain cases it might contribute to less overall emissions if it means that a building won't burn down and need to be replaced." Good old lime plaster could make a comeback.
Drywall is complicated and covers a wide range depending on fire and acoustic ratings, so they took a pass on making a simple chart. But it has a big impact, and we are waiting with bated breath for Breathaboard, the low-carbon alternative.
The floor finishes are full of surprises. Why is laminate so high? And hardwood? At least our two favorite floors—cork and linoleum—come out on top. Or on the bottom, as they do their charts. They are also both the healthiest floors you can buy and have antibacterial properties.
Other Materials and Components
The report discusses windows briefly, noting they add up to 10.9% of the footprint of a house and have significant MCE. They might have noted, as they did with concrete, that the carbon footprint of windows is proportional to their number and size, and that the best window barely beats the worst wall in terms of performance.
So our advice is always to use them sparingly, to design them to frame a view, and size them for well-being and beauty, from the inside out. As I noted previously: "Keep the windows as small as you can get away with and still let in the light and views that you want, with an eye for proportion and scale. And keep it simple."
What can one conclude from all of this?
- Our basements really are carbon icebergs. Between the concrete and the foam insulation, our traditional basement composes a big chunk of footprint for space that is out of sight and often out of mind. This is why I have always said my healthy low-carbon dream house would be built on stilts. We have to rethink this basic issue of how we connect to the ground.
- Last year we showed an experimental room built by Milk Architecture and Design with straw walls, lime plaster, and a metal roof. It is looking prescient.
- Build with radical simplicity, but also with radical sufficiency. How much do you actually need? If you build less, it will cost less, and it will have a smaller footprint.
- We have written before that we should be building out of sunshine. Author and engineer Bruce King says we should be building out of materials that come from the sky: carbon from the carbon dioxide in the air, sunlight, and water, which, through the process of photosynthesis, are turned into plants that we can turn into building materials. These all have the lowest carbon footprints on any of these lists.