Skip to main content

The building industry, and the authorities and regulators that govern it, have finally, reluctantly, begun to accept the importance of embodied carbon. And manufacturers of building products have been kicked and screamed into providing environmental product declarations that tell us how much carbon is emitted during production. But what is the easiest way to control initial carbon in the housing industry?

Treehugger recently wrote about a new, simpler tool called BEAM Estimator for calculating this, if you have a design to enter into it. Perhaps a better place to start is the “Materials Carbon Emissions Guideprepared 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 analysis of 34 homes in the area, which were put through the BEAM estimator. Its purpose is simple: “These product rankings help facilitate low-carbon decision-making by giving consumers an idea of ​​the average amount of carbon emissions associated with different types of products.”

BFCA also said: “This should not be seen as something that replaces a life cycle analysis. Rather, it seeks to offer itself as a starting point for integrating consideration of the carbon emissions of materials into more decision-making processes. » But it is a very useful starting point indeed.

It also starts with these first three stages of initial carbon: “cradle to gate” or raw material sourcing; transport to the factory; and manufacturing. But it’s the biggest chunk of initial carbon (65% to 75%) with the strongest data. This is what BFCA calls Material Carbon Emissions (MCE). “In other words, this guide tells you which materials have less polluting raw material acquisition and manufacturing processes and therefore a lower carbon footprint,” the authors write.

I have previously expressed skepticism of the ECM concept and thought the full initial carbon figures including transport to site and installation should be included. But BFCA’s Chris Magwood told Treehugger why he sticks to the basics: bad data.

“I did more research on my thesis and discovered that the assumptions of the LCA software I was sampling were typically 50% to 150% off in their estimates compared to an actual analysis of how materials move,” said Magwood.

I finally understood the concept. This little book was made for Nelson, BC, but the numbers in it apply everywhere – they’re intrinsic to the hardware, not where you bought it or how you got it. use. And the story he tells will surprise many.

Where is the carbon?.

City of Nelson / Builders of Climate Action

In the houses examined for the guide, we find that they resemble icebergs of carbon, with most of the ECM buried in the foundations and basement. This number will obviously vary depending on where you are building, the depth of the foundations and whether or not there is a basement. The guide shows that you can significantly reduce the carbon footprint of concrete by increasing the amount of slag and fly ash while reducing the amount of Portland cement. But it also underscores something we often stress about Treehugger: our good old principle of radical simplicity.

“One of the most important things to remember when looking to mainstream materials carbon consideration and reduction is the role that building designers, engineers and architects play. These professionals can designing shapes, structures and aesthetics that lead to less carbon from materials. Owners can request or require these considerations. Reducing carbon emissions from materials means applying their consideration as early as possible in the design phase.


City of Nelson, Builders for Climate Action

The fun starts with insulation, which accounts for 15.3% of the carbon footprint of a typical home. Data is presented in a typical Canadian mix of metric and US measurements, showing kilograms of carbon dioxide equivalent 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 foregoing closed-cell spray foam insulation, which was particularly popular in the home improvement world; I have it at home. It has more than three times the carbon footprint of the second largest emitter. (There’s a good article about responsible home improvement contractors ditching things in Green Building Advisor.)

The other shock is that mineral wool has, on average, four times the footprint of fiberglass. For years, green builders have avoided fiberglass. Then manufacturers got rid of formaldehyde binders and increased recycled content, and it started to look better and better. Given that Healthy Building Network found it to be the second healthiest insulator after cork, there’s good reason to review it.

But there’s also all the negative carbon cellulosic insulation, from hemp and newspaper to wood fiber and straw, these are more appealing than ever. Wood fiber is new to North America, but will arrive next year when the TimberHP factory opens in Maine. It could be the next big green thing.

City of Nelson / Builders of Climate Action

Rigid insulation boards, often used below grade or for additional insulation outdoors, tell a different story. Extruded polystyrene (XPS) was a horrible substance until recently when it was reformulated to eliminate hydrofluorocarbon foaming agents and renamed NGX. But when asked if he was back on Magwood’s menu, he told Treehugger that “it’s just less bad.”

To complicate life for the brochure users, they measure rigid insulation at R-5 while they measure wall insulation at R-13. This acknowledges that they are used differently, but masks the fact that even the new and improved NGX foam has 12 times the carbon footprint of fiberglass.


Builders for Climate Action

In Nelson, siding is second only to insulation with 12.5% ​​of household emissions. It was no surprise to learn that brick is terrible, but acrylic stucco was surprisingly high, making it a carbon crime as well as a design crime. Most low carbon siding materials are combustible, a big problem in the West these days.

The study authors note that this could be a price we have to pay: “Although many of these fire-resistant products have high carbon emissions, in some cases it could help reduce overall emissions if it means that a building will not burn down and must be replaced.” The good old lime plaster could make a comeback.

Interior surfaces

Builders for Climate Action

Drywall is complicated and covers a wide range based on fire and acoustic ratings, so they decided to create a simple chart. But it has a big impact and we look forward to the Breathaboard, the low carbon alternative.

Floor coverings are full of surprises. Why is the laminate so high? What about hardwood? At least our two favorite floors, cork and linoleum, come out on top. Or down, as they make their cards. They are also the healthiest floors you can buy and they have antibacterial properties.

Other materials and components

The report briefly discusses windows, noting that they add up to 10.9% of a home’s footprint and have a significant MCE. They might have noticed, 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, design them to frame a view, and size them for well-being and beauty, from the inside out. As I noted earlier: “Keep windows as small as possible while still letting in the light and views you want, keeping an eye on proportion and scale. And keep it simple.”

What can we conclude from all this?

  • Our basements are truly carbon icebergs. Between concrete and foam insulation, our traditional basement makes up a big chunk of footprint for a space that’s out of sight and often out of mind. That’s why I’ve always said that my healthy, low-carbon dream house would be built on stilts. We need to rethink this fundamental question 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 seems prescient.
  • Building with radical simplicity, but also with radical sufficiency. How much do you actually need? If you build less, it will cost less and have a smaller footprint.
  • We have already written that we should build from the sun. Author and engineer Bruce King says we should build from materials that come from the sky: carbon from 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 of any of these lists.

In the end, you don’t need a fancy calculator or a giant spreadsheet. Go to each of these tables and start at the bottom. It really can be as simple as that.