Passive Building Standards–What about Embodied Energy/Carbon?

GWPHIUS Senior Scientist Graham Wright is back this week, this time following up on a comment made to his One Cereal Aisle, Many Cereals post from last week. Reader Sarah Larsen (thanks Sarah!) asked about embodied carbon issues. The answer, we thought, deserved its own post, and we hope, discussion.

First, here’s Sarah’s comment:

Graham, thank you for such a thorough and thoughtful post. As a licensed architect, and CPHC I am already inclined toward the PHIUS methods, but continue to be curious about the nerdy differences, how, and why they came to be. I am also incredibly happy with the relationships being developed between PHIUS and code/regulatory agencies; it is critical that energy-efficient building practices spread beyond the geeky few.

The graph shows per capita energy consumption (kg oil equivalent) vs. per capita GDP, PPP (current international $). The size of the bubbles denotes total poulation per country. All values refer to the year 2011. Courtesy European Environment Agency.

The graph shows per capita energy consumption (kg oil equivalent) vs. per capita GDP, PPP (current international $). The size of the bubbles denotes total population per country. Click to enlarge. Data from the Eureopean Environment Agency and the World Bank.

With that said where is the EMBODIED CARBON calculation in our standards?? I can’t stress enough how important it is that we take this into consideration. There are PHIUS certified buildings being developed touting their energy and sustainable credentials who are using products with CO2e paybacks that will almost certainly never be met. We have just 10 years to get this right – a 90 year ROI is not going to cut it! I am very much afraid that if we develop code requirements with blinders on to anything but energy *consumption* we will have the reverse impact that we are working toward – climate catastrophe – by packing our buildings full of foam rather than thoughtfully balancing carbon footprint throughout a life-cycle assessment (LCA).

LCA has some growing up to do, but tools such as Tally are already making better, more broad-thinking choices available to anyone who cares. It is critical that leaders such as PHIUS be talking about embodied carbon and the up-front resource demands of our built environment. I think we could adapt Michael Pollan’s advice on eating as the best way to consume other resources: Build efficiently; not too much; use mostly plants.-– yours in climate-conscious building – Sarah Larsen

Now, back to Graham:

We are aware of the issue but feel we are not yet to the point where we can outright standardize, that is, make hard and fast rules. The Norwegian Institute for Zero Emission Buildings came up with some different definitions depending on how many building life cycle phases are included.

We can move more aggressively to put up some resources and guidelines. There are a couple of books I have found that seem to be helpful for making design decisions:

Most of the thinking I have seen focuses on materials, but I am not convinced that is a broad enough view of it. Suppose one uses low embodied carbon materials but this requires a lot of expensive skilled labor. The money paid for that fans out into the general fossil-powered economy, which has a certain emissions intensity per dollar, so there are emissions associated with all that economic activity, so maybe you don’t come out ahead.

From that point of view, low-cost construction is low-emission construction, and everyone is trying to do that already. I remember back in 2013 or so, the IEA or the EIA put up an interactive data browser that let you see what they were thinking in terms of scenarios to limit warming to 2 degrees C. It was clear that they were not counting on much of a contribution from the building sector. It’s pretty clear that the reason for this is that the turnover of the building stock is too slow, there just isn’t enough time anymore.

As I recall in their 2 C scenario for the U.S., almost half the total savings came from decarbonizing the generation of electricity. The “electrify everything” movement has strengthened since, Architecture 2030 seems to be on board with that, recognizing that anything done in new construction standards doesn’t do anything about the existing buildings, which is most of the problem within that next-ten-years window — so the priority is to stop emissions from existing buildings by electrifying. This is part of the reason we modified the overall energy criterion for PHIUS+ 2018 — it allows for off-site renewables now and that is compatible with the “electrify everything” idea. Some people, like ILFI, go even further and just ban all combustion from building operations.

But back to the embodied emissions. Here is an idea I had about how that might be written into a rule. Let’s call it PHIUS+ Equity & Carbon 😀

It would address both equity and embodied energy/emissions with adjustment to the Source energy limit based on construction budget, on the idea I mentioned above, that embodied energies/emissions are roughly indicated by how much money is being spent, along with the emissions intensity of the national economy.

The adjustment would be based on the idea of limiting the total operating + embodied, so, operating + embodied < 714+221 = 935 kWh/sf for example.

To generalize:

SE * 70 yr + $CB * NatkWh / NatGDP < 10.2 kWh/sf.yr * 70 yr + $170/sf * NatkWh / NatGDP


SE = modeled net source energy for the project [kWh/sf.yr]   — about 10.2 kWh/sf.yr
$CB = project construction budget [$/sf]   — about $170 /sf, U.S.
NatkWh = National source energy use [kWh]  — about 29 trillion kWh, U.S.

NatGDP = National gross domestic product [$]   — about 19 trillion USD

This is mathematically equivalent to adding a penalty for high-budget construction and a credit for low-budget construction, which is in the equitable direction, on a world wide basis even. The emissions intensity of the Indonesian economy is actually higher than the U.S., I make it out to be 0.44 kgCO2e / USD, while the U.S. is 0.29 kgCO2e/USD. But they catch a break with the above scheme because their cost of construction is a lot lower, about $60/sf instead of $170 for the U.S., so multiply those two numbers together and the Indonesian building industry is putting out 0.44×60 = 26 kgCO2e/sf while the U.S. building industry puts out 0.29×170 = 49 kg/sf.

I switched to carbon accounting for a minute there, but I still prefer source energy accounting. It’s a pretty good proxy for emissions because 80% of the primary energy is coming from fossil fuel burning, but I like that source energy penalizes nuclear for being nonrenewable, whereas straight carbon accounting gives it almost a free pass.

Solving the above equation for Source Energy criterion:

SE < 10.2 kWh/sf + [($170/sf – $CB) / 70 yr] * NatkWh / NatGDP

This would also tend to do a favor for retrofit projects if they are able to save construction cost by reusing the structure — and that is the high-embodied-emission part, for concrete and steel buildings, from a materials point of view. The $170/sf could be generalized to a national average value as well, $NatCB. For residential projects, just substitute for the 10.2 as 3840 kWh/person * ResOcc / iCFA.

Probably only the operating-energy part of it tapers to zero in future. More emphasis can be put on initial-cost/embodied-energy savings by shortening the time frame. At 20 years instead of 70 they are about equal in the initial example. This would favor retrofits even more.

3 thoughts on “Passive Building Standards–What about Embodied Energy/Carbon?

  1. Thank you for addressing Sarah Larsen’s excellent point/question about embodied carbon. As the growing evidence is showing, addressing embodied carbon is proving to be the most urgent priority for construction if we are to address the immediate need to reduce our carbon emissions. This is a challenge for many of us in the high performance building sector, much of which has been laser focused on energy efficiency for so long now. Unfortunately your response makes a few unsubstantiated and I believe incorrect assumptions making the formula you propose not a good tool for looking at EC.

    You say “Suppose one uses low embodied carbon materials but this requires a lot of expensive skilled labor.” You then go on to equate, contrary to much real world experience, the cost of a project to how much EC it has (“that embodied energies/emissions are roughly indicated by how much money is being spent”).

    Firstly, how does using low EC materials require “a lot of expensive skilled labour”? As someone who works for a construction company that builds using the passive house approach with low EC materials that is news to us. If we use dense pack cellulose to fill a wall cavity it doesn’t take more labour time than clearing a building, bringing in workers with hazmat suits and filling the same cavity with foam. Installing wood fibre board isn’t necessarily more labour than foam board. Nor necessarily is making a prefabricated envelope with natural materials more work than a prefabricated system with foam.

    Secondly assuming costs are roughly indicative of EC is another huge unsubstantiated assumption. Higher costs may, in some context, reflect high EC but it is not at all necessarily true and the opposite is often true. A helical pile foundation can almost always beat a concrete slab on grade for cost and definitely for carbon. It is also worth investigating what makes some high EC materials cheaper. Due to massive subsidies to the petroleum industry a number of high EC products are currently relatively cheap. This is true for plastics and foam and vinyl. It is amazing the amount of embodied carbon that ends up in even small cheap builds. As carbon taxes become more common we should see some significant shifts in costs. That said, we have many readily available low EC materials today that can match or beat the cost of the high EC options.

    The claim that embodied carbon/emissions are roughly indicated by how much money is being spent or as you referenced “low-cost construction is low-emission construction” is simply false. A wood fibre insulation board has much lower EC than an EPSboard (and out performs it in significant ways) but is not always as cheap. A plastic chair is probably cheaper than a wooden one but it certainly doesn’t have lower embodied carbon.

    We have been building energy efficient low EC buildings for over a decade and what drives up costs is not some phantom extra labour for using, say a wood fiber board vs a foam board, but factors such as high-end finishes, significant change orders, over glazing, some material choices and other factors that affect all building and construction.

    While there are real challenges to quantifying EC in buildings right now it isn’t hard to make the right and easy choice of focusing on natural, renewable materials. Choosing readily available low embodied carbon materials and design choices provides an instant carbon savings (which is what the world needs right now) versus the decades long potential projected carbon savings from PH projects.

    In this light I urge you and PHIUS to go beyond unsubstantiated assumptions and work hard to promote the reduction of EC based on the excellent research being done internationally on EC, not on some misguided assumption that somehow cheap is low carbon. In addition, a PHIUS retrofit standard, again encouraging low EC materials, would be a great asset towards meeting the building/retrofit targets we all must meet.

    Select embodied carbon resources and research:

    “Bringing Embodied Carbon Upfront: Coordinated action for the building and construction sector to tackle embodied carbon” World Green Building Council

    Embodied Carbon in Buildings: Measurement, Management, and Mitigation
    Editors: Pomponi, Francesco, De Wolf, Catherine, Moncaster, Alice (Eds.) Springer, January 2018

    “Embodied carbon mitigation and reduction in the built environment – What does the evidence say?”
    Journal of Environmental Management Volume 181, 1 October 2016, Pages 687-700
    Francesco Pompon & AliceMoncaster

    “New buildings: embodied carbon”
    Architecture 2030

    Head to Head Heat Test: EPS vs GUTEX vs Mineral Wool – Buffering Summer Heat
    475 High Performance Building Supply

    Turning Buildings Into Carbon Sinks
    2019 Building Energy Boston (a project of the North East Sustainable Energy Association) conference Keynote presentation by Chris Magwood, Ace McArleton, Jacob Racusin.

    “Zero Carbon Isn’t Really Zero: Why Embodied Carbon in Materials Can’t Be Ignored”
    Engin Ayaz and Frances Yang

  2. My main point is that the embodied emissions of construction is not a property of the materials – not those alone – it is a property of the entire building delivery process. We noticed in this GBA writeup about a podcast on embodied emissions this item: “Transport of workers to the job site is the biggest source of emissions.” That is the kind of thing I am talking about.

    Here is an idea what to do about it: Phase 1 – require that all the firms involved in the building delivery are signed up for 100% renewable energy for their own company operations (Architect, Builder, MEP etc), using Power Purchase Agreements or the like. Extra credit for any employees that sign up for it at home. Phase 2 – require that all the immediate suppliers are likewise powered by renewables, the lumberyards and distributors. Phase 3 – require that all the component suppliers down to the materials level are also powered by renewables, until the whole supply chain is covered, including soft costs like Rater fees and EPD certifications themselves.

    It’s just a thought…

    • While I totally agree that we need to have renewable energy powering all stages of the material lifecycle (from designing to harvesting to processing to manufacturing to transporting to installing) it is still a dangerous assumption that higher cost is correlated with embodied carbon, much less a causative relationship.

      National scale data almost never helps make accurate decisions at the local level. The embodied carbon per unit of gross domestic product changes dramatically depending on where you are building and where the materials were made in the first place.

      For instance, when someone plugs their table saw into the grid in Tucson, they are producing roughly 1.8 lbs of CO2 per kWh. When they plug their table saw into the grid in Seattle, they are producing roughly 0.12 lbs of CO2 per kWh (according to EIA data on embodied carbon intensity for various fuel sources combined with the most recent 2017 Power Mix reports available from utilities). However, electricity in Tucson is about $0.03/kWh less than Seattle so the electricity with ~18x the carbon impact per kWh is less expensive. Cheaper often means higher carbon impact.

      To further complicate matters, when I plug in my table saw in Tucson, it is powered by on-site solar so I use near zero carbon impact electricity for free. This is why we need to talk about specific projects, specific materials, specific utilities, etc.

      Bringing it back to embodied carbon: for the cutting phase of installation to be equivalent, it would need to take ~18x longer to cut a material like Gutex woodfiber than to cut rigid foam board.

      (Note: I will use Gutex as an example because I know a lot about it, but there are also carbon storing insulation options like cork, sheep wool, hempcrete, and straw bale. In addition, as noted above, it is critical to have these conversations at a product specific level. For instance, there are a lot of woodfiber insulation solutions that come from poorly managed forests and therefore have a high embodied carbon impact rather than being net carbon storing).

      The truth is that Gutex cuts faster than foam and also installs much quicker overall. The assumption that carbon storing materials take more energy or effort to install is totally bogus. In fact, I’ve found they often save me time and money overall.

      Furthermore, Gutex woodfiber insulation is -5 to -10 lbs of CO2 per CF (based on 3rd party LCA) whereas foam is 5 to 100 lbs of CO2 per CF (also based on 3rd party LCAs). Gutex costs about twice as much as foam upfront, so according to Graham’s proposal, this could mean Gutex is considered as having twice the embodied carbon as rigid foam board. The reality is that foam adds a lot of upfront carbon and Gutex subtracts upfront carbon.

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