7. What is Module D in an EPD?

Module D appears in every EPD but it sits apart from the other life cycle modules. While Modules A, B, and C sit inside the product system boundary tracking impacts that definitely occur, Module D sits outside that boundary, capturing potential benefits from recycling, reuse, or energy recovery that happen after the product leaves the defined system.

This placement isn’t a technicality. It reflects fundamental questions about how to account for recycling and recovery in environmental assessment. Module D is simultaneously one of the most important parts of an EPD and one of the most controversial.

Understanding Module D matters because it often shows the largest numbers in an EPD, particularly for recyclable materials. Steel EPDs might show Module D benefits exceeding all other life cycle stages combined. Ignoring Module D misses critical information. But applying it incorrectly leads to misleading conclusions.

What Module D Actually Contains#

Module D captures environmental benefits and loads that occur beyond the product system boundary when materials or energy leave the system for reuse, recycling, or energy recovery.

Recycling benefits appear when materials get recycled into new products. Producing steel from recycled scrap requires far less energy than producing steel from iron ore. When a steel beam gets recycled at end of life, the avoided impacts of virgin steel production are credited in Module D.

The calculation compares the impacts of producing virgin material versus producing material from recycling. The difference (usually negative, representing benefits) goes into Module D.

Energy recovery benefits appear when materials get incinerated with energy capture. Burning wood waste generates heat or electricity that substitutes for fossil fuel energy. Module D credits the avoided fossil fuel impacts.

The calculation compares the recovered energy to the energy it displaces. If burning construction timber generates electricity replacing coal power, the avoided coal impacts appear in Module D.

Reuse benefits appear when components get directly reused in subsequent life cycles. A steel beam removed from one building and installed in another provides benefits by avoiding new beam production. Module D captures those avoided impacts.

Exported material benefits occur when materials inherently have value in subsequent systems. The biogenic carbon content of timber, the calorific value of combustible materials, or the carbonation potential of concrete can provide benefits beyond the immediate product system.

Why Module D Exists: The System Boundary Problem#

The challenge Module D addresses is real. When you conduct Life Cycle Assessment, you must define system boundaries. What’s inside the system? What’s outside?

For a steel beam, the obvious boundary is cradle to grave: raw material extraction through manufacturing, use, and disposal. But what happens when the beam gets recycled? The recycled steel goes into a new product system. Does that belong to the original beam’s LCA or the new product’s LCA?

If you don’t credit recycling benefits, products designed for recycling show high environmental impacts despite delivering real environmental benefits through material recovery. You’d incentivise designing products for landfill (low processing impacts) rather than recycling (higher processing impacts but significant material recovery benefits).

If you credit recycling benefits fully inside the system boundary, you might double-count them. The original product claims the recycling benefit. The product made from recycled material also claims it uses recycled content (which has lower impacts than virgin material). Both products benefit from the same recycling activity.

Module D solves this by placing recycling benefits outside the system boundary. They’re reported but clearly separated from the product’s direct impacts. This transparency lets users decide how to handle these benefits in their assessments.

EN 15804 is explicit about Module D’s purpose: “Information module D allows a manufacturer to declare information regarding the benefits and loads beyond the product system boundary.” The standard doesn’t mandate whether to include Module D in total impact calculations. It requires reporting it separately so users can make informed choices.

What the Numbers Mean#

Module D values are typically negative (benefits) though they can be positive (loads) in some scenarios.

A steel product showing Module D climate change of -1000 kg CO₂e means recycling the steel at end of life avoids approximately 1000 kg CO₂e compared to producing virgin steel. The negative number represents avoided impacts.

An insulation product showing Module D of -500 kg CO₂e might reflect energy recovery from incineration. Burning the insulation at end of life generates energy replacing fossil fuels, avoiding 500 kg CO₂e.

Module D isn’t always beneficial. A product containing materials that contaminate recycling streams might show positive Module D values, representing additional burdens created beyond the system boundary.

The magnitude of Module D depends on:

• Recycling rate assumptions: 90% recycling versus 50% recycling dramatically changes Module D
• What virgin material is displaced: Recycled aluminium replacing virgin aluminium saves more energy than recycled concrete replacing virgin concrete
• Energy recovery efficiency: High-efficiency energy recovery generates more substitution benefits than low-efficiency incineration
• Technology assumptions: Module D uses current average technology, not best-case or worst-case scenarios

The Calculation Method (EN 15804 Specifics)#

EN 15804+A2 specifies exactly how to calculate Module D:

For material recycling: Module D = (Net material leaving system × Virgin material production impacts) – (Net material leaving system × Recycling process impacts)

The first term is the avoided virgin production. The second term subtracts the recycling processing burden. The difference (usually negative) is the net benefit.

For energy recovery: Module D = (Recovered energy × Impacts of displaced energy source) – (Energy recovery process impacts)

The recovered energy is based on the net calorific value of materials. The displaced energy assumes current average technology (not best available or worst case).

For elementary flows: Biogenic carbon content, carbonation potential, and net calorific value appear in Module D as material properties with potential future benefits or impacts.

The standard explicitly excludes carbon offsets: “Carbon offset shall not be included in the calculation of the GWP.” Module D is about material flows and energy recovery, not purchased offsets.

The Controversial Aspects#

Module D generates debate because it credits benefits that:

Occur in the future. The benefits depend on what actually happens at end of life, which might be 50+ years away for construction products. Recycling infrastructure, technology, and markets could change dramatically.

Depend on external systems. Whether recycling benefits materialise depends on recycling collection, sorting efficiency, processing technology, and markets for secondary materials. None of these are under the product manufacturer’s control.

Involve uncertain scenarios. EPDs must state recycling assumptions (e.g., “70% recycling, 30% landfill based on current practice”). If actual recycling rates differ, real benefits differ from credited benefits. Optimistic scenarios overstate benefits. Pessimistic scenarios understate them.

Create comparison challenges. Product A might show high Module C (end of life) impacts but large Module D benefits, resulting in near-zero net end-of-life impact. Product B might show low Module C and small Module D benefits, also resulting in near-zero net impact. Are they equivalent? It depends whether you believe the recycling scenarios.

Can incentivise problematic design. A product designed for difficult recycling might claim large Module D benefits based on optimistic recycling scenarios that rarely occur. A product designed for durability and longevity might show smaller Module D because it doesn’t need recycling as frequently.

Some critics argue Module D should be abolished because the uncertainties are too large. Proponents argue that ignoring recycling benefits creates worse problems by failing to credit design for recyclability.

How to Use Module D in Decisions#

The question isn’t whether Module D is theoretically perfect. The question is how to use it practically in decision making.

For product comparison: Compare Module D values across products but also check the scenarios. If two concrete products show different Module D, check whether they assume different recycling rates or different end-of-life treatments. Different scenarios might explain the difference more than different product designs.

Consider whether recycling infrastructure exists in your region. Module D benefits based on 80% recycling rate don’t materialise if local infrastructure only achieves 40%.

Assess whether recycled material markets are stable. Module D assumes markets exist for recycled materials. If markets are volatile or absent, benefits are uncertain.

For building-level assessment: EN 15978 for building environmental assessment leaves flexibility in how to handle Module D. You can include it in total calculations, exclude it, or assess it separately.

A conservative approach excludes Module D from base calculations but presents it as additional information showing potential benefits under stated scenarios.

A progressive approach includes Module D where recycling infrastructure is established and markets are stable, particularly for materials with long recycling histories (steel, aluminium, glass).

For specification decisions: Consider Module D as one factor among many. A product with large Module D benefits might be preferable if supporting recycling infrastructure exists. But don’t choose products based solely on optimistic Module D credits while ignoring poor performance in other life cycle stages.

Verify the recycling scenarios are realistic for your context. An EPD showing large Module D benefits based on “90% recycling to virgin-equivalent material” might be overstating benefits if actual recycling produces lower-grade material.

Module D and Biogenic Carbon#

Biogenic carbon creates special Module D complexity for timber and bio-based products.

When trees grow, they absorb CO₂ from the atmosphere and store it as carbon in wood. When wood products reach end of life, several scenarios are possible:

Incineration with energy recovery: The stored carbon releases as CO₂ (appears in Module C), but energy generation avoids fossil fuel use (benefit in Module D).

Landfilling: Carbon might stay stored long-term (benefit in Module D) or decay releasing methane (impact in Module C).

Recycling: Carbon stays stored in new wood products (benefit in Module D through extended storage duration).

EN 15804+A2 requires separate reporting of biogenic carbon impacts within climate change. Module D must declare the biogenic carbon content of materials and account for what happens to that stored carbon beyond the system boundary.

This makes timber EPDs particularly complex in Module D. You might see biogenic carbon storage benefits, energy recovery benefits from incineration, and material recycling benefits all appearing in Module D under different end-of-life scenarios.

Module D in Different Product Types#

Module D significance varies by product:

Metals (steel, aluminium, copper): Large negative Module D values because recycling these materials saves substantial energy compared to virgin production. Steel Module D might be -50% to -150% of Module A1-A3 production impacts.

Glass: Moderate negative Module D. Glass recycling saves energy but less dramatically than metal recycling. Module D might be -20% to -40% of production impacts.

Concrete: Small Module D values. Concrete recycling as aggregate provides modest benefits. Some carbonation benefits might appear. Module D typically -5% to -15% of production impacts.

Timber and bio-based materials: Complex Module D depending on end-of-life scenario. Energy recovery, extended carbon storage, and material recycling create different benefit patterns. Module D can be highly significant, sometimes exceeding production impacts.

Plastics: Variable Module D depending on recycling feasibility. Easily recycled pure plastics show moderate benefits. Mixed or contaminated plastics might show minimal benefits if incinerated or landfilled.

Composite materials: Often low Module D because composites are difficult to recycle. Design that enables disassembly improves Module D by allowing component-level recycling.

Understanding these patterns helps you interpret whether Module D values are reasonable for product types.

Red Flags in Module D#

Some Module D declarations should raise questions:

Extremely large benefits (Module D magnitude exceeding all other modules combined) deserve scrutiny. Check the recycling scenarios. Are they realistic?

Precision without justification. Module D involves substantial uncertainty. Results reported to multiple decimal places imply false precision.

Optimistic scenarios without alternatives. EPDs should ideally present scenarios or explain assumptions. “100% recycling to virgin-equivalent quality” might be overstated if actual practice differs.

Benefits without corresponding Module C impacts. If Module D credits recycling benefits, Module C should show recycling processing impacts. Missing Module C with large Module D suggests incomplete accounting.

Inconsistency with market realities. If recycled material markets are weak or absent, large Module D benefits are questionable regardless of theoretical calculation correctness.

Making Peace with Module D Uncertainty#

Module D will never be perfect because it describes uncertain future benefits outside system boundaries. That uncertainty doesn’t make it useless. It makes it information requiring judgment.

The alternative to Module D is worse: ignoring recycling and recovery entirely. This penalises recyclable products and incentivises single-use design. Module D brings recycling into the assessment transparently, letting users see potential benefits and judge their likelihood.

The key is treating Module D as scenario-dependent information, not guaranteed fact. The EPD states assumptions. You assess whether those assumptions are reasonable for your context. Module D informs decisions but doesn’t determine them.

For materials with established recycling systems (steel, aluminium, glass in regions with good infrastructure), Module D benefits are reasonably reliable. For materials with uncertain recycling futures or products with complex end-of-life, Module D benefits are more speculative.

Practical Takeaways#

When you see Module D in an EPD:

Read the scenarios. What recycling rate is assumed? What end-of-life treatment? Are these realistic for your region?

Compare Module D across similar products using the same scenarios. Differences then reflect product design rather than scenario assumptions.

Consider the magnitude. Small Module D (5-10% of production impacts) matters less than large Module D (50%+ of production impacts) in decision making.

Check Module C. Module D benefits should correspond to Module C processing impacts. Both should tell a consistent end-of-life story.

Assess infrastructure. Do recycling systems exist for this material in your region? Are markets stable?

Be consistent. If comparing products, treat Module D the same way for all options. Include it for all or exclude it for all, don’t cherry-pick.

Module D represents the uncertain but real environmental dimension of recycling and recovery. Understanding what it measures, why it exists, and how to interpret it helps you use EPDs effectively rather than being confused by negative numbers sitting outside the system boundary. The uncertainty is real, but ignoring Module D entirely misses critical information about product end-of-life potential.