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Building Matters

Measuring Embodied Carbon

Tools for determining a project's upfront carbon emissions to help inform materials selection—and the challenges of employing them

This straw-bale house designed by Arkin Tilt Architects is a net-zero energy design that also uses materials that sequester carbon. A new calculator aimed at helping designers and builders select materials with low embodied carbon is due for release at the end of February. Photo courtesy Edward Caldwell.

A Canadian builders’ group says it is nearly ready to unveil its long-awaited database on embodied carbon in building materials, giving builders and designers one more tool for reducing the oversized contribution the industry makes to global climate change.

The BEAM calculator has been in the planning and development stage since 2018 under the direction of Chris Magwood, the executive director of a sustainable building school in Ontario called the Endeavour Centre. Barring any unforeseen snags, Magwood says, the software will be available at the website of Builders for Climate Action by the end of February.

“It turns out that getting into the software business is just as hard as the house contracting business,” Magwood said in a telephone call. Three people have been devoting most of their time to wrapping up the software while another half-dozen have been reviewing and critiquing the work and otherwise trying to wrap things up.

The release comes at a time when an increasing number of architects and builders are shifting their attention from “operational carbon,” meaning the greenhouse gas emissions connected with heating and cooling buildings, to “embodied carbon,” the emissions that can be attributed to manufacturing and transporting building materials such as concrete, steel, wood, and plastics. As Magwood and others have argued, as operational carbon declines with steady improvements in building efficiency, embodied carbon in building materials becomes more important in the near term. To keep global warming under 1.5ºC, the point at which scientists fear irreversible change takes place, builders will have to start using materials with less embodied carbon as well as those able to sequester carbon.

BEAM stands for “building emissions accounting for materials” and is intended to help builders and designers estimate greenhouse gas emissions in materials they use to build a house. It will be among a number of calculators available to the industry—tools already on hand include the Carbon Leadership Forum’s EC3 Tool and the Living Future Institute’s Declare labeling program (both of which are free) as well as commercially available products that come with subscription fees.

“It’s going to be a super tool,” Marc Rosenbaum, a Massachusetts-based engineer and energy consultant, said of BEAM. “Just pick the materials you’re using and know how much [to calculate]. That is a huge leap for most people.”

Separately, the Passive House Network has announced a tool bar add-on for Excel allowing Passive House designers to calculate embodied carbon when they’re using the Passive House Planning Package (PHPP), the modeling software used by designers. The software, called PHribbon by AECB CarbonLite, costs $234.

Although the Endeavour Centre had considered requiring users to become members of Builders for Climate Action in order to gain access to the tool, organizers ultimately decided against it. “We realized the world doesn’t need another green building membership organization,” Magwood said. “What it really needs is a tool. So, we just adjusted the business model so it can be freely available.”

Users need not be computer wizards to use BEAM, Magwood said. After plugging in the dimensions of the building—including such variables as floor and window areas—the program offers all the possible materials that each assembly in the building could potentially be made of. Designers can see the carbon impact of each choice, and work their way through the building assembly by assembly. Users can create a number of versions of the plan in order to compare the carbon impacts of using different materials.

The data used in BEAM comes from the environmental product declarations, or EPDs, compiled by manufacturers and verified by a third party.

Screen shot of BEAM carbon tool
A screen shot from the BEAM carbon calculator, due for release by the end of February. Illustration courtesy Chris Magwood / Builders for Climate Action.

A changing conversation

The drive to build super-efficient houses can be traced back to the 1970s and the Saskatchewan Conservation House in Canada. Aided by plummeting prices for solar energy, the race for net-zero buildings has since gone into overdrive. But the importance of embodied carbon in building materials has emerged only in the last several years, part of what Magwood calls a “stunning” change in the conversation about the role that buildings play in driving climate change. The New Carbon Architecture, a book written in part and edited by Bruce King, helped advance the conversation. Published in 2017, the book lays out the case for using building materials that sequester carbon, such as wood and other plant-based products, rather than materials that are responsible for emitting large amounts of carbon when they are manufactured, such as steel and concrete. (For a podcast featuring King and Magwood discussing the book, go here.)

Magwood and many others have since written about the urgency of reducing emissions related to building materials if the rise in global temperatures is to be kept to less than 1.5°C. The benefits of net-zero-energy construction and very low operational carbon just don’t pay off quickly enough. Some 2 trillion sq. ft. of new buildings and major renovations are expected before 2050. In an early chapter of the book, Erin McDade writes that even if all new construction is twice as energy efficient as usual, between 80% and 90% of the energy profile will come from embodied, not operational, carbon. “How we value and evaluate its embodied carbon is crucial,” McDade writes.

In 2019, Marin County, California, adopted requirements for low-carbon concrete intended to lower greenhouse gas emissions. But neither the National Association of Home Builders (NAHB), the country’s biggest trade group for residential builders, nor the International Code Council (ICC), which develops model building codes in the U.S., seems interested in a low-carbon campaign now. The Canadian Home Builders’ Association has been equally disinterested, Magwood said.

For the moment, that leaves any effort to promote lower levels of carbon in building materials largely to groups like the New Building Institute, the Energy & Environmental Building Alliance, the Carbon Leadership Forum (which published a report on reducing embodied carbon last year), the Northeast Sustainable Energy Association, and to individual builders and designers.

“Embodied carbon policy is pretty nascent right now,” says Matt Jungclaus, one of the authors of a Rocky Mountain Institute report on embodied carbon published in 2021. Jungclaus, who left RMI to pursue a PhD at the University of Colorado Boulder, is now working to develop benchmarks that would quantify the carbon footprint of code-built houses. Quantifying where the industry is now is a first step in developing strategies for carbon reductions in the future.

“It becomes really complicated really quickly,” he said of introducing carbon requirements into building codes. “We haven’t really figured out what will work on the basis of affecting every single-family home in the country or an individual state. I don’t think we know what that looks like yet because we don’t have the benchmarks, and if we did, there would be a lot of variables regionally.”

Rule of thumb vs. calculations

Some builders are taking steps to reduce carbon now. GBA has contacted smaller design and construction firms that seem to follow what California architect Jeffrey Adams of Atmosphere Design Build calls a “more qualitative than quantitative” approach to lowering embodied carbon.

“We do not rigorously quantify the embodied carbon of the materials we specify [in the same way Living Building Challenge projects do],” he said in an email. “Our firm is operating at such a small scale that we do not obsess over carbon numbers, but we are strategically weaning our material specifications off petroleum-based materials as much as possible (i.e. less foam).”

Armando Cobo, a Texas-based designer of zero-energy ready houses, struck a similar note. In addition to building in features that reduce energy consumption, Cobo uses reclaimed and recycled materials, and locally sourced products “that minimize the emissions resulting from the harvesting, manufacturing, and transportation [of goods].”

While working in larger markets, such as the Dallas-Fort Worth area, Cobo said he can order concrete made with fly ash or ground granulated blast slag to reduce the amount of cement, a major contributor to concrete’s big carbon footprint. “Unfortunately,” he added, “few cement and concrete producers make these products available throughout the country.”

Rachel White, the CEO of Byggmeister, a renovation and design company in the Boston area, said her firm has already taken the biggest step toward lowering embodied carton—staying away from new construction completely. When houses are renovated rather than replaced, most structural elements along with the foundation are reused, eliminating the worst carbon offenders that most new buildings must have. Writing in The New Carbon Architecture, Larry Strain estimates that renovating a building produces between 50% and 70% less carbon than building a new one.

“We’re starting off one step ahead,” White said. “We’ve already decided we don’t build any new buildings. We started off as remodeling contractors, and we’ve made a very conscious decision to stay remodeling contractors, and we rarely do additions.”

Even with renovations, however, there are new materials and new assemblies to consider and when a company uses the same approach in multiple buildings, the carbon calculations may be transferable from one project to the next. Byggmeister, for example, developed a low-carbon approach to attic renovations that eliminated some of the spray polyurethane foam it once used in favor of an assembly that mixes dense-pack cellulose (a carbon sink) with a thinner layer of spray foam. To design that assembly, she said, the company did the homework comparing embodied carbon, and it could apply the same calculations to similar jobs in the future.

“We did that once,” she said. “We don’t feel that we need to do that again. Some things are well known and well understood. We know that cellulose is better than foam, for example, and if we can use cellulose instead of foam, we should do so. On the other hand, I think there are some things that are not well understood. And that’s when you do need to do the calculations and you may be surprised. What you think is an approach that’s going to be better may not be better.”

Sometimes using old rules of thumb or making assumptions can backfire, Rosenbaum said.

“After 40 years of doing energy-related stuff I have experience and a good academic background and have done a lot of measuring of buildings,” he said. “I am really good at shoot-from-the-hip, and I’d get at least a B+ [on energy estimates] without doing math. But when it comes to embodied carbon, my intuition is ground zero. Zilch.”

For example, he cited a 10,000-sq.-ft. early childhood center designed and built by South Mountain Co. on Martha’s Vineyard. The roof was built with 16-in. deep I-joists, which Rosenbaum originally thought he would insulate with dense-pack cellulose. But he was nervous enough about the possibility that the cellulose would settle in the damp, coastal climate that he decided to use blown-in fiberglass instead. That would require a ventilation layer above the roof deck, including a second layer of sheathing to support the roofing. When the job went out for bid, the insulation contractor recommended spray foam because it would be tens of thousands of dollars cheaper than adding that second layer of sheathing. Spray foam, of course, is the boogie man of low-carbon advocates so the idea wasn’t very appealing.

“I said, ‘Let’s just do the math to know how much worse we’re making it,’” he said. “To make a long story short, if you’re not using spray foam with a blowing agent that has a high global-warming potential, which it’s traditionally been but isn’t now, then the fiberglass was higher in embodied carbon.” So, the roof ended up mostly insulated with low-density spray foam and some closed-cell foam with a better carbon outcome than it would have been with blown-in fiberglass at the density required in this deep sloped roof.

Similarly, wood is typically heralded as the slam-dunk replacement for steel and concrete because it sequesters carbon. That holds true for structural elements, but Rosenbaum isn’t so sure that all wood products are better than the alternatives. Moreover, he believes that the discussion of carbon in relation to forest management and forest products needs a lot more research. Wood products that may appear better from a carbon point of view can turn out differently—such as the amounts of wood pellets produced in the forests of southeastern U.S. to power massive biomass power plants in Europe.

“My tuition just isn’t that good,” he said. “I think we need to be careful. We need to do the math. And we need to think about it like we think about energy, which is: where does the next dollar spent on embodied carbon reduction get us the most value?”

Advice for small builders

So, should even smaller builders and design firms be relying on rules of thumb, or should they be doing spreadsheets and calculations with tools like the BEAM calculator or some of the others already available?

“As both an engineer and an environmentalist, I always struggle with that question,” Jungclaus said. “I want to say you should do the number crunching but I think rules of thumb are OK, as long as you think about them over time and allow them to shift. If you have a rule of thumb today that says you should buy concrete that has X percent cement replacement like fly ash, then that rule will be different in a few years. Be cautious of how those rules change over time, because this is a fast-moving market.”

He made these suggestions for builders with a limited budget or limited time for carbon counting:

  • Make yourself aware of what low-carbon materials are available in your area with a tool like EC3 or BEAM.
  • If you have a standard approach and tend to use the same type of assembly on job after job, and don’t have the time or money to change, make sure the materials that you’re using are the best versions of those materials from a carbon point of view.
  • If you do have more resources available, work with a designer or engineer to come up with specific suggestions for reducing embodied carbon.

In markets where buyers are generally interested in sustainable building practices, moving toward low-carbon designs can be a “huge selling point” by giving builders compelling talking points. And it doesn’t necessarily take a complete change in approach to substantially reduce the carbon impact of new buildings.

“You don’t need bleeding-edge zero-carbon steel to build a net sequestering house,” Jungclaus said. “Homes have much lower structural requirements than tall buildings. If you can offset the concrete you need for the slab or the crawlspace or you can use alternative materials in your climate, you can tip those scales to net sequestering pretty readily. Small buildings have the highest potential to net sequester carbon right now.”

Challenges for bigger builders

For larger construction companies, moving toward building assemblies with less embodied carbon isn’t as simple as it might seem. But for Doug Tarry Homes in Ontario, carbon reduction feels like a logical next step after making gains with water and energy efficiency. The company builds some 250 single-family houses a year in and around St. Thomas, a city of 39,000 midway between Toronto and Detroit, and is now laying the groundwork for a systematic, company-wide plan for lowering carbon content.

“We figured out energy, and we’ve figured out water management,” Miyoko Oikawa, the company’s manager of research and innovation, said in a video call. “We’ve done that. What’s the next step? As a company, we’re really focused on this next level of building performance.”

The initiative, she said, has come from the company’s president, Doug Tarry, whose father started the firm, and a shared sense of urgency in the company about climate change. In order to understand how to move forward, the company is working with Magwood to benchmark the embodied carbon currently in the company’s low-rise buildings (Doug Tarry also builds mid-rise projects). Magwood has completed an initial analysis, giving the company a starting point for making carbon cuts. Oikawa says they’ll have to consider comparable costs and availability while making sure that replacement products, while lower in carbon, won’t compromise the durability and life span of their buildings.

The company hasn’t studied the problem in enough depth to draw up firm plans for reducing its carbon footprint, but Oikawa said the company probably will be able to reduce embodied carbon by as much as 60% over the next year or two. Most of that would come from using more cellulose and less foam insulation, and by using concrete mixes that replace up to half the cement with granulated blast-furnace slag. Those two steps alone, she said, would make a big difference.

But change comes slowly to the industry. Oikawa, who worked previously with the Ontario Home Builders’ Association, said: “From an industry standpoint, it’s difficult to invest in carbon-reduction strategies when you don’t know what stance the code may take, or a municipality. There’s still a lot of discussion on that level—what methods are we using to quantify? If I have an energy target, how does that affect a carbon target? There’s real resistance from the industry itself in creating targets without doing enough of an analysis up front to make sure that these are thoughtful and implemented in a way that is achievable for every building in every area. Right now, we don’t have enough people who can do those calculations.”

Stefanie Coleman, Doug Tarry’s chief sustainability officer and a former president of the Canadian Home Builders’ Association, pointed to other issues that can slow a transition to low-carbon materials. One is a lack of EPDs for whole categories of building materials, such as plumbing and mechanicals, making it difficult to compare the carbon content of different materials that could be used in the same application. In addition, builders are struggling with an ongoing shortage of skilled trades, which can complicate any plans to adopt new materials or new technologies.

“Even though builders or developers may want to make changes there’s a learning curve that needs to be applied,” she said, “some education that needs to be passed down to the trades that are doing the work. Especially in a super-hot market, when we have a shortage of trades, to change something is highly risky, just for practical purposes.”

And, she added, supply chain problems compounded by COVID have made whole product lines unavailable for a month at a time.

“COVID is not an excuse,” she said, “it’s a reality.”

The path forward

Bruce King’s book talks at length about low-tech building materials that can store carbon rather than emit it (in his words, materials that are “made from the sky”), such as wood, clay, straw, and mushrooms. Some of them are readily available and can be one-for-one swaps with materials that have a lot of embodied carbon. Cork insulation, for example, sequesters carbon while extruded polystyrene and closed-cell spray foam with an HFC blowing agent are carbon emitters.

RMI’s 2021 report on carbon details a number of low-cost and no-cost substitutions that can lower embodied carbon substantially. Choosing concrete mixes carefully, for example, can lower carbon emissions by as much as 33% with little or no increase in cost. Switching insulation may yield a carbon savings of 16% with no cost premium.

Yet some materials that builders would love to use are either hard to get or very expensive. Wood-fiber insulation board, for instance, is made by a single North American company, MSL in the province of Quebec, but no one in the U.S. makes it, at least for now. A Maine-based company hopes to start production of some wood-fiber insulation products this year; at the moment, U.S. builders have to order from a European manufacturer through a U.S. retailer. It’s expensive. Likewise, straw makes an excellent carbon-storing building material, and there are manufacturers turning out straw and wood panels that can be used something like a structural insulated panel, only without the foam. EcoCocon is one such producer. Its panels come in a variety of configurations and a standard thickness of 15 ¾ in. (R-38.3). Its U.S. distributor, Build With Nature, says the lead time for delivery ranges from four to five months, and the panels will cost $17.80 per sq. ft. (not including transportation).

New building products, even very good ones, can fall into a black hole somewhere between their creation and the big-box store, never to be seen again. Yet the new technologies finding their way into the marketplace, along with products still in their infancy, are intriguing, to say the least. Many useful products are widely available now, Magwood said, including cellulose, fiber-board insulation, cork flooring and linoleum, and concrete in which carbon dioxide has been injected at the ready-mix plant. Barriers to developing new products are not technical but on a business scale, he said. Market demand, encouragement from government, carbon credits, and the like will help bring new ideas to light.

“There’s everybody from people who are really keen on it and really pushing to be leaders, to people who are interested and want to follow soon but are not quite yet all the way there, to the people who will dig their heels in and not want to make any changes at all,” he said. “We’ve seen the arc before with both energy efficiency and healthy materials. Once those early adopters start doing it, eventually the whole curve gets dragged along.”

Discouragement is part of the picture, given the magnitude of the climate challenge. Then again, Magwood periodically comes across something that he’s never seen before—like a mycelium tube nearly as strong as a 2×4, developed in the inventor’s basement without so much as a $50 contribution from industry or government. That gives him reason for optimism.

“The real threshold is the industry’s eagerness to embrace it and the R&D and the funding and the support to make these new materials come along,” he said. “There is quite a bit of hope because I think there are a lot of other industries where the solution itself isn’t even clear yet. The building industry has the great advantage of knowing what the solution is: You have to make energy-efficient, airtight buildings out of low-carbon or carbon-storing materials, and we know what a bunch of those materials are right now, and we know what the next generation of them looks like, and if we push hard we can get there faster, and we know there are a whole bunch of other ones on the near horizon.”


Scott Gibson is a contributing writer at Green Building Advisor and Fine Homebuilding magazine.

14 Comments

  1. Nick Defabrizio | | #1

    This is a great first step. We have to do this if we are serious about climate change....

    A complete system would also include all the embedded carbon in the infrastructure needed for a particular house. Where I am people are putting in 1000 foot driveways to get to their energy efficient new home with the 40 foot concrete swimming pool......and clearing trees to do it...

    1. Charlie Sullivan | | #3

      Another piece to include is the tradespeople driving trucks to the site each day. That might seem inevitable, but there are options to consider such as parking a trailer at the site for the duration of the project and driving there in small cars, possibly car/vanpooling to bring workers to a site if it's in a different region from where most of them live. And increasing the use of factory-built modules or panels.

      1. Nick Defabrizio | | #5

        Good point!

  2. Expert Member
    Armando Cobo | | #2

    Really good article, Scott. Thank you for an eye opening summary.
    Carbon-neutral homes are designed with material and energy reduction in mind. This encompasses FREE passive solar design, low or lower carbon material production and selection, systems and processes that help reduce energy consumption, and a home that produces the same amount of renewable energy that it expends, creating zero carbon emissions.
    Limiting carbon-intensive materials by avoiding products with high carbon footprints like steel, concrete, aluminum, plastics, and foam insulation, and/or a thoughtful use is essential.
    Choosing lower carbon alternatives to build structures by utilizing optimum value engineering, wood framing efficient structural trusses and engineer wood products. Same with eco-friendly, sustainable and recyclable material claddings, like wood, brick or siding.
    Maximize your structural efficiency applying optimum value engineering, wood framing efficient structural trusses and engineer wood products.
    The bottom line is that today, with little time spent deliberating about the right building processes, selecting low-energy materials and adding renewables to our homes, we can easily achieve over 60% savings in our homes total embodied energy and carbon reduction, and a lot more with on-site renewables.
    The best part of designing and building Zero Energy Ready homes is that we have most of our clients achieving this level of efficiency, healthy homes and lower carbon footprint for no additional cost, and few for about 1% more. No excuses!

    1. GBA Editor
      Kiley Jacques | | #4

      Armando, do you track carbon in your projects? If so, what software do you use?

    2. Expert Member
      Armando Cobo | | #6

      @Kiley – Personally, I don't. We did had a couple of projects awhile back that the Homeowners hired consulting firms to do complete LCA analysis. Base on their information, we chose regular materials that have low carbon emissions. I do recall that both carbon emission reductions were around 60%. They also noted that with one house having PV at 95% annual consumption and the second at 106%, most of all the carbon emissions were offset.
      The full cost of doing an LCA on all projects, is unfortunately, something few residential clients are willing to pay for. The way I design houses today, with all materials and systems being almost the same as those two houses, I’m pretty confident we’re achieving similar goals.

      1. Nick Defabrizio | | #7

        But in the end isn't this mostly about reducing concrete and steel? of course, one would want to reduce waste of all sorts where ever possible, but ultimately, isn't most of the imbedded carbon in concrete and steel?

        1. Charlie Sullivan | | #8

          Mostly, but foams can also contribute. Majorly, with the wrong blowing agent, or less dramatically through their polymer content.

      2. GBA Editor
        Kiley Jacques | | #12

        Armando,

        I interviewed Stacy Smedley last week. She is one of the creators of the EC3 carbon calculator. She walked me through the software a bit--it was edifying to learn how products compare, how many categories there are to measure, what kind of emission reductions are possible, where to source vetted products, and how much work goes into gathering and sharing this data (for free). It was a hopeful-feeling conversation. I mentioned as much to Scott Gibson, who made an excellent point: "The key will be builder interest."

      3. Expert Member
        Armando Cobo | | #13

        Kiley - As you found out, one can spend a lot of time doing the research, so it takes a client, homeowner or Builder, heavily invested in carbon reduction, to hire someone to do all that work, and pay for it. I know I don't have the time for it, and if I did, I definitely wouldn't do it for free.

  3. Andrew Frederick | | #9

    More cheerleading for my builder peers here than trying to promote, but I started an on-shore U.S. company making offsite compressed straw panels this past year, and the market demand is through the roof, though straw requires some interesting problem-solving to make a homogenous panel. so- PLEASE, guys and gals, apply your ingenuity and make some too, the market is there. There really isn’t a better bang for your embodied carbon buck than straw.

    1. Expert Member
      Malcolm Taylor | | #10

      Andrew,

      I don't know a lot about it, but something like what you are doing would seem to me to be exactly what straw needs to achieve more widespread use. Maybe GBA will do a feature on it?

      1. GBA Editor
        Kiley Jacques | | #11

        Malcolm, I had a similar thought and did a little poking around to see what I might learn about Andrew's product. I wasn't successful. Andrew, if you'd like to chat, email me at [email protected].

        1. SidneyN | | #14

          It's too bad your latest GBA article about Andrew's panels is behind the GBA Prime paywall, as I have been interested in strawbales and worked on a couple of stawbale buildings in Maryland about 10 years ago. The main issue with straw is the R-value is only about 1.45/inch (based on ORNL test in 1998). I look forward to hearing how Andrew's panels test.

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