6. Understanding EPD Impact Categories (Beyond Carbon)

When you look at an EPD, you’ll see environmental impacts reported across multiple categories, not just carbon emissions. Climate change sits alongside acidification, eutrophication, ozone depletion, resource depletion, water consumption, and various other indicators. This multi-impact approach distinguishes EPDs from simpler carbon footprints.

The multiple categories exist because environmental impact is multi-dimensional. A product with low carbon emissions might consume massive amounts of water or deplete rare minerals. A product with high carbon might have minimal acidification potential. Understanding what each category measures and why it matters helps you interpret EPD data properly and make informed decisions.

This isn’t academic complexity for its own sake. Different impacts matter in different contexts. Water consumption is critical in water-scarce regions but less pressing where water is abundant. Acidification matters where ecosystems are sensitive to pH changes. Resource depletion matters for materials facing supply constraints. Looking at carbon alone misses these dimensions.

Why Multiple Impact Categories Matter#

Climate change dominates environmental discourse, and carbon dioxide equivalents get the most attention. This focus makes sense given climate change’s global scale and urgency. But it’s not the whole picture.

Consider two insulation products. Product A has 20% lower carbon emissions than Product B. If you only look at climate change, Product A wins. But Product A might use substances that deplete stratospheric ozone or generate toxic emissions during manufacturing. Product B might use benign materials with slightly higher energy requirements.

Which is genuinely better? The answer depends on context, priorities, and local environmental conditions. The multi-category approach lets you see tradeoffs and make informed choices rather than optimising for one impact while ignoring others.

European regulations increasingly require multi-impact assessment. EN 15804+A2 mandates reporting multiple categories specifically to prevent narrow carbon optimisation that creates problems elsewhere. The standard forces transparency across environmental dimensions.

How Impact Categories Work: Characterisation#

Impact categories use characterisation models that convert physical flows (emissions, resource use) into equivalent impacts using common units. This lets you aggregate different substances affecting the same environmental problem.

For climate change, hundreds of greenhouse gases get converted to carbon dioxide equivalents (CO₂e) using global warming potentials. Methane’s CO₂e factor is about 28 over 100 years, meaning 1 kg of methane has the same climate impact as 28 kg of CO₂. Nitrous oxide’s factor is about 265. These characterisation factors let you add up contributions from all greenhouse gases.

The same principle applies to other categories. Acidification converts sulphur dioxide, nitrogen oxides, ammonia, and other acidifying substances to equivalents. Eutrophication converts nitrogen and phosphorus compounds to equivalents.

EN 15804+A2 specifies which characterisation methods must be used for construction product EPDs. These come from the European Commission Joint Research Centre and are identified as “EN_15804” methods. This standardisation ensures all EPDs in the system use identical calculation approaches, making results comparable.

Other EPD systems might use different characterisation methods. North American EPDs often use TRACI (Tool for Reduction and Assessment of Chemicals and Other Environmental Impacts) methods. Older EPDs might use CML or ReCiPe methods. When comparing EPDs, check that impact assessment methods match or understand how differences affect results.

Core Impact Categories#

EPDs typically report these main categories:

Climate Change (Global Warming Potential)#

What it measures: Greenhouse gas emissions contributing to global temperature increase. Reported in kg CO₂e (carbon dioxide equivalents).

Key contributors: Carbon dioxide from fossil fuel combustion and process emissions, methane from biological processes and leaks, nitrous oxide from fertilisers and combustion, fluorinated gases from industrial processes and refrigerants.

Why it matters: Climate change drives sea level rise, extreme weather, ecosystem disruption, and human displacement. It’s the most widely regulated environmental impact globally.

For construction products, climate change impacts typically dominate in Module A1-A3 from energy-intensive manufacturing processes. Cement and steel show particularly high values because of both energy use and process emissions. Timber products might show negative values if biogenic carbon storage is considered.

EN 15804+A2 splits climate change into three sub-categories: fossil, biogenic, and land use change. This separation provides transparency about carbon sources. Biogenic carbon from timber and bio-based materials follows special accounting rules.

Typical ranges: Vary enormously by product type. Insulation might be 5-50 kg CO₂e per square metre. Concrete might be 300-500 kg CO₂e per cubic metre. Steel might be 2000-4000 kg CO₂e per tonne.

Ozone Depletion Potential#

What it measures: Emissions of substances that destroy stratospheric ozone, which protects Earth from harmful ultraviolet radiation. Reported in kg CFC-11 equivalents (reference to trichlorofluoromethane).

Key contributors: Chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), halons, methyl bromide. Most of these substances are now banned or restricted under the Montreal Protocol.

Why it matters: Stratospheric ozone depletion increases UV radiation reaching Earth’s surface, causing skin cancer, cataracts, and ecosystem damage. The Montreal Protocol successfully reduced ozone-depleting substance emissions, but legacy uses and substitutes remain.

For most modern construction products, ozone depletion values are extremely small or zero. Historic insulation products using CFC blowing agents showed significant values. Modern alternatives use substances with zero or minimal ozone depletion potential.

Typical values: Often scientific notation (1.2 × 10⁻⁸ kg CFC-11 eq) because values are tiny. Products using modern materials typically show effectively zero ozone depletion.

Acidification Potential#

What it measures: Emissions that contribute to acid deposition (acid rain), lowering pH of soil and water. Reported in kg SO₂ equivalents or mol H⁺ equivalents.

Key contributors: Sulphur dioxide from fossil fuel combustion, nitrogen oxides from combustion and industrial processes, ammonia from agricultural activities and some manufacturing.

Why it matters: Acidification damages forests, lakes, and buildings. It releases toxic metals from soils, harms aquatic life, and degrades materials. Particularly significant where ecosystems have low buffering capacity.

For construction products, acidification typically correlates with energy use from fossil fuels. Products manufactured using coal power show higher acidification than those using cleaner energy. Transport contributes through NOₓ emissions from diesel combustion.

Typical ranges: Building materials might show 0.5-5 kg SO₂ eq per functional unit. Energy-intensive products or those using coal-based electricity show higher values.

Eutrophication Potential#

What it measures: Nutrient enrichment of water bodies causing algal blooms, oxygen depletion, and ecosystem disruption. Often split into freshwater, marine, and terrestrial eutrophication. Reported in kg PO₄ equivalents or mol N equivalents.

Key contributors: Nitrogen compounds from combustion, fertiliser production, and wastewater. Phosphorus from detergents, fertilisers, and industrial processes.

Why it matters: Eutrophication creates dead zones in water bodies where oxygen depletion kills aquatic life. Algal blooms produce toxins harmful to humans and animals. Affects drinking water quality and ecosystem health.

For construction products, eutrophication often comes from energy production (NOₓ emissions) and raw material extraction. Products involving agricultural inputs might show higher values from nitrogen fertiliser use.

EN 15804+A2 reports eutrophication in three categories: freshwater (kg PO₄ eq), marine (kg N eq), and terrestrial (mol N eq). The separation reflects different mechanisms and affected environments.

Typical ranges: Values vary by sub-category. Freshwater eutrophication might be 0.001-0.01 kg PO₄ eq. Marine and terrestrial show different units and magnitudes.

Photochemical Ozone Creation Potential#

What it measures: Formation of ground-level ozone (smog) from volatile organic compounds and nitrogen oxides reacting in sunlight. Reported in kg NMVOC equivalents (non-methane volatile organic compound) or kg ethylene equivalents.

Key contributors: VOCs from solvents, paints, fuels, and industrial processes. NOₓ from combustion. These react in sunlight to form tropospheric ozone.

Why it matters: Ground-level ozone causes respiratory problems, damages crops, and harms ecosystems. Different from beneficial stratospheric ozone. Particularly problematic in urban areas with high VOC and NOₓ emissions.

For construction products, coatings, adhesives, and products involving solvents show higher photochemical ozone creation. Manufacturing processes using or emitting VOCs contribute. Transport emissions add NOₓ.

Typical ranges: Might be 0.1-2 kg NMVOC eq per functional unit, varying substantially by product type and manufacturing process.

Abiotic Depletion Potential#

What it measures: Consumption of non-renewable resources, split into fossil fuels and mineral/metal resources. Reported separately for elements (kg Sb eq, antimony equivalents) and fossil resources (MJ).

Key contributors: Extraction of metals, minerals, coal, oil, natural gas. Scarcity and extraction difficulty affect characterisation factors.

Why it matters: Non-renewable resources have finite availability. Depletion threatens long-term supply security and increases future extraction difficulty and environmental impact. Critical for materials with limited reserves or concentrated sources.

For construction products, resource depletion reflects metal content (steel, copper, zinc), fossil fuel use for energy, and rare elements in specialised products. Products with high recycled content show lower depletion because recycling reduces demand for virgin extraction.

Typical ranges: Fossil fuel depletion might be 1000-10,000 MJ per functional unit. Mineral depletion varies from negligible for abundant materials to significant for products containing rare elements.

Water Use/Scarcity#

What it measures: Freshwater consumption, sometimes weighted by regional water scarcity. Reported in cubic metres (m³) or water scarcity footprint.

Key contributors: Direct water consumption in manufacturing, cooling, and cleaning. Indirect water consumption in upstream processes and energy generation. Irrigation for bio-based materials.

Why it matters: Water scarcity affects billions of people. Industrial water consumption competes with agricultural and domestic needs. Regional context matters enormously. Water use in water-scarce regions has greater impact than in water-abundant areas.

For construction products, water use varies by process. Wet processes, cooling requirements, and some extraction activities consume substantial water. Products manufactured in water-scarce regions show higher weighted impacts.

EN 15804+A2 now requires reporting water use as a specific indicator, recognising its growing importance.

Typical ranges: Might be 1-100 m³ per functional unit depending on product and processes. Context determines whether values are significant.

Additional Environmental Indicators#

Beyond the core impact categories, EN 15804+A2 requires additional indicators:

Particulate matter emissions measures fine particle pollution affecting respiratory health. Reported in disease incidence or kg PM2.5 eq.

Ionising radiation quantifies radioactive emissions and exposures. Reported in kBq U-235 eq. Relevant for products where nuclear energy contributes to manufacturing.

Ecotoxicity (freshwater) addresses toxic substance releases harmful to aquatic ecosystems. Reported in comparative toxic units (CTUe).

Human toxicity covers cancer and non-cancer toxic effects on human health. Split into cancer effects (CTUh) and non-cancer effects (CTUh).

Land use measures land transformation and occupation impacts on biodiversity and ecosystem services. Various reporting approaches exist.

These additional indicators reflect expanding understanding of environmental impacts beyond traditional categories. They address health impacts, ecosystem effects, and emerging concerns.

Resource Use and Waste Indicators#

Alongside impact categories, EPDs report resource consumption and waste generation as descriptive indicators rather than impact assessments:

Material use: Renewable and non-renewable materials consumed (kg)

Energy use: Primary energy from renewable and non-renewable sources (MJ)

Water consumption: Direct and indirect freshwater consumption (m³)

Waste generation: Hazardous and non-hazardous waste produced (kg), with breakdown by treatment (recycled, incinerated, landfilled)

These aren’t environmental impacts themselves but they provide context for interpreting impacts and understanding resource efficiency.

Interpreting Impact Values: Context Matters#

Raw numbers without context don’t tell you if impacts are significant. A climate change value of 500 kg CO₂e might be high for a small component or low for a large structural element.

Compare within product categories. EPD values make most sense when comparing similar products serving the same function. Insulation products’ values should be compared to other insulation, not to structural steel.

Consider the functional unit. A product reporting per kilogram looks different from one reporting per square metre or per performance unit. Convert to common bases before comparing.

Look at relative magnitudes across categories. If climate change is 1000 kg CO₂e and acidification is 2 kg SO₂ eq, you can’t directly compare these numbers. But you can see which category dominates relative to similar products.

Check against benchmarks if available. Some product categories have established performance ranges. Values at the low end of the range indicate better performance. Values at the high end suggest room for improvement.

Assess in building context. Individual product impacts matter less than building-level impacts. A product with moderately high production impacts but excellent use stage performance might deliver lower total impacts than alternatives.

When Impacts Conflict: Making Tradeoffs#

Products rarely optimise all impact categories simultaneously. Improvements in one area often create tradeoffs elsewhere.

A product might reduce climate change impacts by using renewable energy but increase water consumption in the process. Another might lower resource depletion through recycled content but show higher toxicity from recycling processes. A third might minimise transport impacts through local sourcing but use less efficient regional manufacturing.

How you weigh these tradeoffs depends on context and priorities:

Regional conditions affect which impacts matter most. Water use in desert regions matters more than in rainy climates. Acidification in areas with sensitive soils matters more than in well-buffered regions.

Regulatory focus might prioritise certain impacts. If carbon pricing applies but other impacts aren’t regulated, climate change gets more weight in decisions.

Project-specific goals influence priorities. A project targeting net zero carbon focuses on climate change. A project near sensitive water bodies prioritises eutrophication and ecotoxicity.

Life cycle perspective matters. Short-term production impacts might be outweighed by long-term use stage benefits across multiple categories.

There’s no universal formula for weighting impacts. EPDs present data across categories. You make informed decisions based on your context.

From Impact Categories to Decisions#

Understanding what the numbers measure transforms EPD tables from meaningless data into decision-support information.

When reading an EPD, scan across impact categories to see the profile. A product might show:

• High climate change, high acidification, moderate eutrophication = energy-intensive manufacturing with fossil fuels
• Low climate change, high water use, moderate resource depletion = renewable energy manufacturing with water-intensive processes
• Low across most categories, high human toxicity = benign production process but potentially problematic substance content

This profile guides questions. High water use prompts asking where manufacturing occurs and if water scarcity is an issue. High toxicity prompts investigating which substances drive the impact and if alternatives exist.

The multi-category view reveals whether improvements in one area came at the cost of problems elsewhere. It prevents narrow optimisation that shifts burdens between impact categories.

The Limits of Impact Categories#

Impact categories capture major environmental concerns but they’re not exhaustive. They don’t cover social impacts like labour conditions. They don’t address animal welfare. They may not capture emerging issues like microplastic pollution unless those fit within existing toxicity categories.

Characterisation models involve scientific judgment and uncertainty. Different impact assessment methods make different assumptions. Results should be understood as indicators rather than absolute truth.

Some impacts are inherently local (eutrophication in a specific water body) while others are global (climate change). The characterisation factors often aggregate these, potentially masking location-specific significance.

Despite limitations, the multi-category approach provides far better environmental insight than single-indicator assessments. It forces consideration of multiple environmental dimensions and makes tradeoffs visible.

Building Your Impact Category Literacy#

Understanding impact categories improves through practice. Read EPDs for products you know well and think about why certain categories show high or low values given what you know about manufacturing processes.

Compare EPDs within a product category to see typical ranges and understand which categories show significant variation between products. This reveals where design and manufacturing choices matter most.

Consider the physical processes behind products. Energy-intensive manufacturing drives climate change and often acidification. Water-intensive processes drive water use. Ore extraction drives resource depletion. These relationships help you develop intuition for reading results.

Remember that impact categories exist to enable comprehensive environmental assessment. They’re tools for understanding tradeoffs, identifying improvement opportunities, and making informed decisions across multiple environmental dimensions. Learning to interpret them transforms EPDs from opaque technical documents into genuinely useful information.