By Katia Lucuy
In our first article, The Fundamentals of Embodied Carbon, we unpacked what embodied carbon is, why it matters and how it’s quietly shaping the environmental legacy of every building we build. We explored the carbon footprint journey of gypsum board and introduced life cycle assessments (LCAs) as the most powerful tool we have to measure and manage these impacts.
In this second article, we take that next step. If LCAs tell the carbon story of a product, then Environmental Product Declarations (EPDs) are the chapters we actually get to read. But like any technical document, EPDs come with their own language, assumptions and pitfalls. From industry averages to product-specific data, from GWP to system boundaries, we’ll break down what these documents really mean and how to use them to make informed, lower-carbon design decisions. Because in a world flooded with green claims and confusing acronyms, clarity is very helpful.
Environmental Product Declarations
By now, you’ve probably come across the acronym EPD, short for Environmental Product Declaration. It’s one of the most valuable tools we have in understanding embodied carbon. But in a world saturated with sustainability acronyms, it’s easy to get lost.
First, let’s clear up a common confusion. EPDs are not the same as HPDs, or Health Product Declarations. While both are useful, they serve entirely different purposes. An EPD focuses on a product’s environmental impact, especially its carbon emissions, while an HPD discloses chemical ingredients and health hazards. Despite this, they’re often used interchangeably, even by professionals. If you’ve ever heard someone, ask for an “HPD” when they meant “EPD,” you’re not alone.
Then there’s the even more mystic territory of “carbon neutral” claims. Some products proudly boast that their materials are net-zero or carbon neutral while in small print it says, “upon request.” But what does that really mean? Often, it refers to carbon offsets (an unverifiable promise that emissions have been “canceled out” by planting trees or funding renewable energy elsewhere). Without a detailed and transparent LCA, these claims are difficult, if not impossible, to verify.
That’s where EPDs come in. A legitimate EPD is third-party verified, follows a strict methodology and provides transparent data on a product’s environmental impact across multiple stages of its life cycle. It’s built using a Life Cycle Assessment and must follow specific Product Category Rules (PCRs), which standardize how different types of materials are assessed.
But just as my mentor, Susan Kaplan, Director of Materials Technology and Sustainability Advisor at HLW, says, not all EPDs are created equal. Some are industry-wide averages, representing a general product type across multiple manufacturers. These are useful for early-stage decisions, but not enough when you need project-specific data. For serious embodied carbon reduction, what you want is a product-specific EPD, one that reflects the actual product you’re specifying, from the actual factory where it’s made. These are the declarations that can back up manufacturer claims and contribute toward certifications like LEED, WELL and Zero Carbon.
In short: don’t be dazzled by glossy green marketing. If a material claims to be sustainable, low-carbon, or climate-positive, ask to see the EPD. If it doesn’t have one, it’s a red flag.
Understanding Units And Metrics
When we talk about embodied carbon, the metric that anchors almost every conversation is GWP (Global Warming Potential) measured in kilograms of carbon dioxide equivalent, or kg CO₂e. But what does this number actually capture?
GWP is a way to express the climate impact of multiple greenhouse gases, not just carbon dioxide (CO₂), but also more potent gases like methane (CH₄) and nitrous oxide (N₂O). These gases trap significantly more heat in the atmosphere than CO₂ alone. For instance, methane can be over 30 times more impactful than CO₂ over 100 years. To make these impacts easier to compare, scientists translate them into a common unit CO₂e so we can measure all greenhouse gases on the same scale.
This single metric becomes the spine of Life Cycle Assessments and Environmental Product Declarations. But while the unit is standardized, the context in which it’s used can vary, making interpretation just as important as the number itself.
Take, for example, the time horizon over which GWP is measured. Most LCAs in the building industry assume a 60-year service life. This helps capture not just the emissions that happen during manufacturing and construction, but also any emissions tied to maintenance, repairs, or end-of-life processes over decades of building use. The 60-year baseline brings consistency and helps compare the long-term impact of different design choices.
Still, even with this standardization, embodied carbon data can be misleading if you don’t pay attention to how it’s framed.
One of the most common mistakes in interpreting LCA data is comparing numbers without checking the context. If one EPD reports emissions per kg of product and another per square foot of installed area, the comparison becomes meaningless, like comparing the sugar in a spoonful of honey to an entire slice of cake.
This is where functional units and system boundaries come in. A functional unit defines what is being measured (e.g. 1 square meter of wall assembly for 60 years) while system boundaries define how much of the life cycle is included (e.g. just production vs. full cradle-to-grave). If you don’t align both, you’re not comparing apples to apples, you’re comparing apples to entire orchards.
In a world where sustainability decisions are increasingly driven by data, clarity in metrics is more than technical rigor. It’s a matter of making better, fairer and more impactful choices.
Embodied carbon is no longer a niche concern for sustainability consultants; it’s a core part of the climate conversation in architecture and construction. Beyond the metrics and acronyms, it’s also a powerful opportunity. Every wall assembly, every ceiling tile, every substitution or reuse decision is a chance to reduce emissions before a building is even occupied.
When we shift our mindset from compliance to creativity, embodied carbon becomes a design challenge, not a constraint. It’s a new layer of authorship, allowing architects, developers and their partners to shape not just the physical form of buildings, but their environmental legacy.
In the next article, we’ll step beyond carbon to explore the other impact categories captured by life cycle assessments, like acidification, ozone depletion and human toxicity. These often overlooked metrics reveal how our material choices affect not just the climate, but ecosystems and human health. We’ll also share some simple, actionable strategies that designers can apply early in a project to drive meaningful carbon reductions without sacrificing performance or aesthetics.
The more we understand the story behind the materials we choose, the better equipped we are to change the ending.
