A Delicate Balance: Weighing Embodied vs. Operational Carbon

While the carbon impact of a building’s entire life cycle is critical, emissions averted by 2030 have an even more significant beneficial impact on our climate than those averted later. This is because emissions are cumulative, and we have a limited time to reduce them.  The good work we do now may keep us from reaching an increase in global temperature that would trigger several climate tipping points.  If we cannot achieve our 9- to 10-year emission reduction goals to keep the warming under 1.5°C, there will be severe and irreversible damage, including permafrost loss and diebacks of the Boreal forest, Amazon, and coral reefs (see Figure 1).  Among other results, a large amount of stored carbon and methane will be released, making efforts to keep the planet habitable for its current populations that much more difficult. Now is the time to act.

Given this limited timeframe, a development’s embodied carbon (EC)—the emissions associated with material extraction, product manufacturing, transport, and construction—takes on an outsized importance. In fact, if we continue with business as usual, EC will make up almost half of the emissions associated with construction in the next 30 years.  Indeed, for a new building built today, EC represents the majority of its impact in the critical next nine years.  To optimally reduce the carbon emissions from a given project, we think it is imperative to holistically balance EC and operational carbon (OC), ensuring they are evaluated concurrently, rather than solving for one at the expense of the other—although sometimes that’s a tricky balance to achieve, because they can require conflicting strategies.

In our practices—Magnusson Architecture and Planning and Bright Power—we’ve had considerable experience and success in reducing our OC—specifically through applying Passive House building principles. Still, EC is too large a slice of the pie to ignore; just one commonly used building material, concrete, makes up roughly 8% of global carbon emissions. So, as an architect and sustainability consultant, we have been negotiating this delicate balance between EC and OC. In part one of this two-part article, we are laying out our framework for how we are addressing both EC and OC. In part two we will be showing how we apply this framework to a new affordable housing development, as an example. We will also explain how this approach can increase equity, especially in the urban affordable housing context. At Magnusson Architecture and Planning and Bright Power, we are interested in presenting ideas that teams can employ immediately, cost-effectively, and with minimal impact on their processes.

Because of the time-sensitive nature of this issue, we’re framing this conversation around a project case study with a ten-year timeframe to better understand EC emitted now versus the entire operational lifetime of the project. When we focus on the more immediate term, we can identify our contributions to the triggers of irreversible climate change and reveal the key mechanisms for carbon reduction now. These key mechanisms, which can be considered low-hanging fruit, have shown reductions in EC emissions of up to 20-45% as compared to business-as-usual for no more than a 1% cost premium.

We will start with a look at the context and the current state of the science of calculating EC.  It is important for those in construction industry professions to be comfortable with the processes and evolution of this science and its reporting structure, so that they can contribute to its development.

Life Cycle Assessment

EC, or the global warming potential (GWP) of a particular material or product, is just one calculated impact studied under the science of life cycle assessment (LCA).  LCA “is a standard method of tracking and reporting environmental impacts of a product or process throughout its full life cycle” (ISO 2006a:8).  It does not capture all environmental impacts (extractions and emissions to and from nature) but quantifies typically five to eleven types, one of which is global warming potential. An LCA’s standard aim is to capture these impacts over the entire life of a material or product, from the extraction of raw materials to the end of life.  These stages are defined as A1-3 Product, A4-5 Construction, B1-7 Use, C1-4 End of Life, D Reuse (referred to as the system boundary) (see Figure 2).  All stages and all impacts are important to assess.  Yet, to address EC over the next nine years, we focus on the results of an LCA in terms of GWP in stages A1-A3 (referred to as “cradle to gate”).

Environmental Product Declaration

The scientific discipline of LCA is only a few decades old and was born out of the principles of industrial ecology.  The standard method of reporting LCA impacts is with an environmental product declaration (EPD), of which there are several types (see Figure 3).

EPDs do not evaluate a product or determine if it passes a certain impact threshold; they are only reporting documents.  Initially, industries created EPDs for internal documentation.  Only more recently are EPDs used in comparisons across products and product categories. ISO standards regulate their creation, the most useful of which at the moment is ISO 14025, which requires the EPD to be third-party verified and “product-specific”.

Product Category Rule

The ISO standard for EPDs establishes that a product category rule (PCR) must be created first.  The industry creating the product agrees on the PCR and defines exactly what is calculated in the system boundary of the LCA, in other words, the “methodological choices made in developing the inventory and converting it to environmental impacts.”1 The PCRs are defined by their own ISO standards and must be detailed enough that two different parties can produce the same LCA results.  Most PCRs right now allow for generic or secondary data to be used for some upstream data (earlier stages of a product).  However, as policymakers and construction industry professionals seek immediate carbon savings, there is increasing demand for more specific data such as facility-specific or supply chain-specific EPDs.  Real savings can be leveraged if procurement is defined by more specific data, as comparison products may be dramatically different if this data is revealed. Although industry has the best expertise to create PCRs, consumers and designers should be aware of the process so they can advocate for information they believe is needed. For example, the PCR for wood products does not require the forest (or tree plantation) management or certification to be included.  Yet, this information dramatically affects the carbon impact (not to mention biodiversity and ecosystem health) of wood products.  (The Carbon Leadership Forum published an informative white paper in July 2021 on the current status of EPDs: “EPD Requirements in Procurement Policies”.)

EPDs can be compared to evaluate GWP between products, but only if they are aligned in several aspects first.  The compared EPDs must:

• follow the same product category rule representing the same life cycle stages,

• not be outdated (typically there is a ten-year validity lifespan), and

• represent products that are functionally equivalent, meaning they perform the same action with no other products missing from the comparison.

There are currently two methods of calculating impacts: Traci or Cml, and thus one must check if the EPDs align here as well.  Finally, there is a careful review of additional data outlining the potential impacts on data quality (such as geographic range) and limitations (impacts not quantified) before conducting the comparison.  In the absence of facility or supply chain specific EPDs, manufacturers disclose this information in the additional data sections in response to demand and the development of legislation such as Washington State’s HB 1103.

Ideally, EPDs are used as the primary data for a whole building life cycle assessment (WBLCA) that allows the evaluation of trade-offs between different systems and environmental impacts. But for many teams, this is currently an expensive and time-consuming endeavor.  Nonetheless, even when EPDs are not used in a WBLCA, they significantly empower the industry to make informed carbon impact decisions immediately as they evaluate a project's embodied and operational emissions.

The project example presented in the second half of this article will employ the component method of using EPDs to evaluate product choices.  For affordable housing in New York City, design occurs within some established parameters that work well for the locale and typology.  Working within that framework, we can still make immediate and dramatic improvements on the GWP impact of each component we typically use, even in a high material content Passive House/Near Net Zero performing building.

An extremely useful tool for teams seeking to optimize components is the Embodied Carbon in Construction Calculator (EC3 tool). It allows a team to track material quantities and associate these with EPDs from a comprehensive public database.  Teams can search the EPD database for a certain product and view the range of available GWP options.  For example, teams can search for a specific product sourced from their area, like a concrete mix, and can see the range of GWP impacts of available products.  Empowered with this information, teams can set targets for their projects.  While the science of LCA reporting standards is becoming ever more accurate, the resulting GWP must not be viewed so much as a literal number but rather as an order of magnitude, useful for comparisons.

The EC3 tool reports the level of uncertainty in the data—made visually clear by whisker graphs—depending on its specificity and quality.  It is a free tool, still in Beta form, with thousands of users. Incubated by the Carbon Leadership Forum (CLF), the nonprofit Building Transparency now runs the EC3 tool. CLF sets GWP baselines for each product category every year and reports them.  While most products will fall below the mark, that baseline is a good starting point for developing carbon caps or reductions. In the second part of this article, we will discuss how we used the EC3 tool in our example project. You will also see how business-as-usual was defined using the baselines for some materials for which we did not have a specific product EPD. (For those who rely on the PHPP for energy modeling, PHribbon can be used to pull EC information directly into the PHPP model using the Embodied CO2 module, which utilizes data from the Building Transparency EC3 database and the U.S. Environmental Protection Agency.)

Low-Hanging Fruit

In part two we will also be covering in-depth the low-hanging fruit components we considered and studied as part of our project example. These components make up some of the key mechanisms identified by CLF/RMI in their 20-45% reduction target scenarios and include:

• concrete,

• CMU,

• steel,

• drywall,

• insulation (roof, wall, sub-slab),

• windows (glazing, installation), and

• refrigerants.

By diving deeply into each of these components studied (over the ten-year time frame), we’ll highlight the trade-offs and decision-making levers unearthed by comparing and balancing the EC versus OC impacts of the design changes explored. This study puts into context the reduction opportunities immediately available, especially to similar high-performance, high-density multifamily housing building typologies. Covering the design process from schematic through construction documentation, the project case study will provide critical emerging research related to each component topic area.  Finally, we will outline the impacts passive design, electrification, and other OC movements have on the immediate EC contribution to study where we can accomplish lower versions of both (see Table 1).

This is an all-hands-on-deck moment for the climate, but construction industry professionals have an incredible opportunity to make a difference. As we noted here, there are tools and strategies available right now to significantly reduce a project’s immediate term carbon impact. We look forward to illustrating how this process works in part two of this article.