A simple guide to carbon emissions from building materials

The construction industry, along with the authorities and regulators that govern it, has finally, reluctantly, begun to accept the importance of embodied carbon. Building product makers have been dragged, kicked and screamed, to provide environmental product data that tells us how much carbon is being emitted in production. But what is the easiest way to deal with elemental carbon in the housing industry?

Treehugger recently wrote about a new and easier tool called BEAM Estimator to calculate it, if you have a design to input. Perhaps the best place to start is the “Material Carbon Emissions Guide” by Builders of Climate Action (BFCA) – the same team behind the BEAM Estimator tool.

This small annotation was written for Nelson, British Columbia, Canada — 169 miles north of Spokane, Washington — and is based on an analysis of 34 homes in the area, which were powered by a BEAM Estimator. Its purpose is straightforward: “These product ratings help facilitate low-carbon decisions by giving consumers an idea of ​​the average amount of physical carbon emissions associated with different types of products.”

The BFCA also stated, “It should not be seen as something to replace life cycle assessment. Instead it seeks to present itself as a starting point for incorporating consideration of physical carbon emissions into further decision-making.” But it is indeed a very useful starting point.

It also begins with those first three stages of elemental carbon: “cradle to gate” or the supply of raw materials; Transportation to factory and manufacturing. But this is the bulk of elemental carbon (65% to 75%) with the most solid data. This is what the BFCA calls Material Carbon Emissions (MCE). In other words, this guide tells you which materials have fewer raw materials and emissions-intensive manufacturing processes, and therefore have a smaller carbon footprint.

I have previously expressed my doubts about the MCE concept and thought that the full raw carbon numbers, including transport to site and installation, should be included. But BFCA’s Chris Magwood explained to Treehugger why he sticks to the basics: bad data.

“I dived deep in my thesis and found that the assumptions in the LCA program I was testing were typically 50% to 150% wrong in their estimates compared to the actual analysis of how the materials moved,” Magwood said.

I finally got the concept. This guide was made for Nelson, British Columbia, but the numbers in it apply anywhere – they are intrinsic to the material, not where you buy it or how you use it. And the story you tell will surprise a lot of people.

Where is the carbon?
Climate Action Builders

In homes checked for evidence, we found them to be like carbonaceous icebergs, with the bulk of the MCE buried in foundations and a basement. Obviously, this number will vary depending on where you build, how deep the foundations are, and whether you have a basement at all.

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 points to a point that we focus a lot on in Treehugger: the good old radical principle of simplicity.

“One of the most important things to remember when seeking to incorporate consideration and reduction of carbon emissions is the role that building designers, engineers, and architects play. These professionals can design the shapes, structures, and aesthetics that result in reduced physical carbon emissions. Homeowners can request or request these considerations.” Reducing material carbon emissions means applying their considerations as early in the design phase as possible.”


Climate Action Builders

The fun begins with insulation, which makes up 15.3% of the typical home’s carbon footprint. The data is presented in a typical Canadian mix of metric and US measurements, showing kilograms of CO equivalents per 100 square meters of insulation area at R-13, with an insulation rating of an R value per inch. The diamond represents the average. Sometimes there are ranges due to different products in the same category.

One can immediately see why clever builders saved closed aerosol foam insulation, which was especially loved in the world of renovation; I have it in my house. It has more than three times the carbon footprint of the next largest emissions. (There is a good article about responsible renovation contractors abandoning the stuff on the green building advisory.)

Another impact is mineral wool, which, on average, has four times the footprint of fiberglass. For years, environmental builders have avoided using fiberglass. Then the manufacturers got rid of the formaldehyde bonds and increased the recycled content, and it started looking better and better. Given that Sanitary Construction Mesh has been found to be the second most hygienic insulating material after cork, there are good reasons to look at it again.

But then there are all the carbon-negative cellulose insulators, from hemp and newspaper to wood fibers and straw – these materials look more appealing than ever. Wood fibers are new to North America but will roll out next year when the TimberHP plant opens in Maine. It could be the next big green thing.

Climate Action Builders

Rigid sandwich panels, often used below grade or for additional insulation outside, tell a different story. Extruded polystyrene (XPS) was a horrific material until recently when it was reformulated to eliminate HFC foaming agents and renamed NGX. But when asked if he’s back on Magwood’s list, he tells Treehugger it’s “less bad.”

To make life difficult for brochure users, they measured solid insulation at R-5 while they measured wall insulation at R-13. This realizes that they are used differently, but obscures the fact that even the new improved NGX foam has 12 times the carbon footprint of fiberglass.


Climate Action Builders

At Nelson, cladding behind insulation accounts for 12.5% ​​of household emissions. There was no surprise in learning that the bricks are horrible, but the acrylic plaster was surprisingly loud, making it a carbon crime as well as a design crime. Most of the low carbon cladding materials are combustible – which is a big problem in the West these days.

The study authors note that this may be a price we have to pay: “Although many of these fire retardant products are high in carbon emissions, in some cases they may contribute to a reduction in overall emissions if it means that the building will not burn. And it needs to be replaced.” Good old plaster can come back.

inner surfaces

Climate Action Builders

Drywall is complex and covers a wide range depending on fire and sound ratings so they took to creating a simple scheme. But it’s making a huge impact, and we’re eagerly awaiting Breathaboard, the low-carbon alternative.

The floors are full of surprises. Why is the laminate so high? And hard wood? There are at least two of our favorite floors – cork and linoleum – upstairs. Or below, as they do their charts. They are also the healthiest floors you can buy and have antibacterial properties.

Other materials and components

The report discusses windows in brief, noting that they add up to 10.9% of the home’s space and have a large MCE. They may 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 hardly beats the worst performing wall.

So our advice always is to use it in moderation, to design it to frame a view, and sized for luxury and beauty, from the inside out. As I noted earlier: “Keep the windows as small as you can move away from them while still letting in the light and views you want, focusing on proportion and scale. And keep it simple.”

What can one conclude from all this?

  • Our basements are really carbonate icebergs. Between concrete and foam insulation, our traditional basement makes up a large portion of the footprint of a space that is out of sight and often out of mind. This is why I have always said that my healthy, low-carbon dream home will be built on stilts. We need to rethink this fundamental question of how we relate to Earth.
  • Last year we featured an experimental room built by Milk Architecture and Design with thatched walls, lime plaster and a metal ceiling. It looks insight.
  • Build with radical simplicity, but also radical sufficiency. How much do you really need? If you build less, it will cost less, and will have a smaller footprint.
  • We wrote before that we should build from the sun’s rays. Author and engineer Bruce King says we must build from materials that come from the sky: carbon from carbon dioxide in the air, sunlight, and water, which, through photosynthesis, turn into plants that we can turn into building materials. All of these have the lowest carbon footprint 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 can really be that simple.

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