EPD Life Cycle Modules A1 to D Explained Simply

Every Environmental Product Declaration (EPD) has a table full of codes like A1, A3, B4, C2 and D. If you've ever wondered what they mean, you're not alone.

These codes are EPD modules. Each one stands for a stage in a product's life, from digging up raw materials to recycling the product decades later. Once you know them, an EPD becomes much easier to read and compare.

This guide explains every EPD module in plain words. You'll also learn which modules matter most, what "cradle to gate" means and how to avoid the most common comparison mistakes.

Why EPDs Use Modules

A building product has a long life story. It starts in a quarry or mine, passes through a factory, travels to a site, sits in a building for decades and finally gets removed.

Each stage creates its own environmental impact. So the European standard EN 15804 splits that story into clear modules. That way, everyone reports the same stages in the same order.

This shared structure makes EPDs comparable. It also lets designers add up results across a whole building, stage by stage.

The Four Life Cycle Stages at a Glance

EPD modules fall into four main stages, plus one extra module that sits outside the product's life.

Now let's look at each one in a little more detail.

Product Stage: A1, A2 and A3

This stage covers everything up to the factory gate.

• A1 – Raw material supply. Mining, quarrying, farming or harvesting the materials.

• A2 – Transport to the factory. Moving those materials to the manufacturing site.

• A3 – Manufacturing. Turning raw materials into the finished product, including energy and packaging.

Most EPDs report A1–A3 together as one combined column. And for most building products, this stage creates the biggest share of the carbon footprint. That's why many green building tools focus on A1–A3 first.

Construction Stage: A4 and A5

This stage covers the trip to site and the work of installing the product.

• A4 – Transport to the building site. Trucks, ships or trains carrying the product to the project.

• A5 – Construction and installation. Site energy, installation waste and the packaging thrown away on site.

In the GCC, A4 can matter a lot for imported products. A product shipped from far away may carry much more transport carbon than a local one. So locally made products with EPDs can stand out here.

Use Stage: B1 to B7

This stage covers the product's working life inside the building. It has seven modules:

• B1 – Use. Emissions from the product while in use, such as gases released from some materials.

• B2 – Maintenance. Cleaning and routine care.

• B3 – Repair. Fixing damage.

• B4 – Replacement. Swapping the product for a new one when it wears out.

• B5 – Refurbishment. Major upgrades or renewal.

• B6 – Operational energy use. Energy the product uses to run, such as for pumps or lifts.

• B7 – Operational water use. Water the product uses to run, such as taps or toilets.

Many EPDs leave some B modules undeclared, marked as "MND" (module not declared). That's often fine. A concrete block, for example, uses no energy to operate, so B6 doesn't apply.

However, B modules matter a lot for some products. Flooring may need replacing several times in a building's life, so B4 can add up. Equipment like chillers uses energy every day, so B6 can be huge.

End-of-Life Stage: C1 to C4

This stage covers what happens when the building comes down or the product gets removed.

• C1 – Deconstruction or demolition. Taking the product out of the building.

• C2 – Transport. Moving the waste to a processing site or landfill.

• C3 – Waste processing. Sorting, shredding or preparing material for reuse or recycling.

• C4 – Disposal. Landfill or incineration of what's left.

These modules often look small next to A1–A3. But they can matter a lot for some products. Timber, for example, may release stored carbon at end of life. So reading C1–C4 gives you a more honest picture.

Module D: Benefits Beyond the Building

Module D works a little differently. It shows the possible benefits and loads beyond the product's own life.

For example, recycled steel from a demolished building can replace new steel in a future project. That avoids the impact of making new steel. Module D shows that potential saving, often as a negative number.

One important rule: Module D is reported separately. You shouldn't add it to the A, B and C totals. It shows potential future benefits, not impacts that happen within the product's own life.

Cradle to Gate vs Cradle to Grave

You'll often see these terms on EPDs. They describe how many modules the EPD covers.

• Cradle to gate: Covers A1–A3 only, from raw materials to the factory gate.

• Cradle to gate with options: Covers A1–A3 plus some extra modules, such as A4 or C1–C4.

• Cradle to grave: Covers the full life, A1 to C4, often with D as well.

Under the newer EN 15804+A2 version, most construction product EPDs must now declare A1–A3, C1–C4 and D, with a few exceptions. So newer EPDs usually tell a fuller story than older ones built to EN 15804+A1.

Which EPD Modules Matter Most?

The answer depends on the product.

1. For most materials, like concrete, steel, glass and insulation, A1–A3 drives the biggest share of impact.

2. For imported products, A4 can add a noticeable amount.

3. For short-life products, like some flooring and finishes, B4 replacement can add up over 50 or 60 years.

4. For energy-using equipment, B6 often outweighs everything else.

5. For timber and bio-based products, C3 and C4 matter because stored carbon may return at end of life.

6. For recyclable metals, module D can show strong future benefits.

So don't stop at A1–A3 if the product's life story points elsewhere.

Common Mistakes When Comparing EPD Modules

Modules make EPDs comparable, but only if you compare the right ones. Watch for these mistakes:

• Comparing A1–A3 with A1–C4. One shows the factory stage only, the other shows the full life.

• Adding module D to the total. It should stay separate.

• Ignoring MND. "Module not declared" doesn't mean zero. It means no data.

• Ignoring replacement. A cheap product replaced three times may carry more carbon than a durable one.

• Mixing EN 15804+A1 and +A2 EPDs without noting the method difference.

Avoid these, and your comparisons will hold up in front of assessors and clients.

How Manufacturers Can Use Modules Wisely

For manufacturers, modules also show where to improve. A big A3 value points to factory energy. A big A4 value points to transport. A strong module D shows the value of recyclable design.

So the EPD becomes more than a compliance document. It becomes a map for cutting impact. The data behind it comes from a life cycle assessment, which models every module in detail.

Manufacturers who want a full, module-by-module EPD often work with experienced teams. Specialists such as Envirolink prepare EPD certification for GCC manufacturers, built to the latest EN 15804 rules.

Final Thoughts

EPD modules look technical at first. But they simply tell a product's life story in clear, numbered chapters: make it, deliver it, use it, remove it and recover it.

So read A1–A3 first, then check the modules that matter for that product. Keep module D separate, and never treat MND as zero. With that, you can read and compare any EPD with confidence.

Frequently Asked Questions

What do A1, A2 and A3 mean in an EPD?

A1 covers raw material supply, A2 covers transport to the factory and A3 covers manufacturing. Together, they form the product stage, from raw materials to the factory gate. Most EPDs report them as one combined A1–A3 column, and this stage usually creates the largest share of a product's carbon footprint.

What is module D in an EPD?

Module D shows the potential benefits and loads beyond the product's life, such as recycling, reuse or energy recovery. For example, recycled steel can replace new steel later. Module D often shows a negative value. You should report it separately and never add it to the A, B and C totals.

What does cradle to gate mean?

Cradle to gate means the EPD covers modules A1 to A3 only, from raw material extraction to the factory gate. It leaves out transport to site, use and end of life. Cradle to grave EPDs cover the full life, from A1 to C4, and usually include module D too.

Which EPD modules are mandatory?

Under EN 15804+A2, most construction product EPDs must declare modules A1–A3, C1–C4 and D, with a few exceptions. Other modules, such as A4, A5 and B1–B7, remain optional and depend on the product and its PCR. Older EN 15804+A1 EPDs often declared only A1–A3.

What does MND mean in an EPD?

MND stands for "module not declared". It means the EPD gives no results for that stage. It does not mean the impact equals zero. Many EPDs leave some use stage modules undeclared because they don't apply, such as operational energy for a concrete block.

Why is A1–A3 the most used figure?

A1–A3 usually creates the largest share of a product's carbon footprint, and almost every EPD reports it. That makes it the most reliable figure for quick comparisons. Green building tools often focus on it first. However, full life cycle results give a more complete picture for many products.