Allocation (Multifunctionality)
A refinery takes in crude oil and emits one cloud of carbon — but out the other end come petrol, diesel, jet fuel, and bitumen. So how much of that carbon belongs to a litre of petrol? There is no meter that measures it. Someone has to decide how to split the shared burden, and the rule they pick can change a product’s footprint many times over.
That decision has a name. Allocation is the process of dividing the emissions of a multifunctional process among the several products or functions it delivers.
Allocation is how a life-cycle assessment divides the shared emissions of a process among its co-products or functions — needed whenever one process yields more than one useful output. ISO 14044 sets a hierarchy: first avoid allocation by subdividing the process or expanding the boundary; then partition by a physical relationship (mass, energy); and only as a last resort by economic value. The method matters enormously — it can change a footprint several-fold — so a PCR fixes it for a category.
Definition — Dividing a Shared Burden
Allocation is the process of partitioning the input and output flows of a process — its energy, materials, and emissions — between the product under study and the other products or functions that the same process delivers. In the language of ISO 14044, it applies wherever a process is multifunctional: it produces more than one thing of value, and the single stream of environmental burden has to be shared out among them.
Allocation is not a measurement — it is a modelling choice, and that is what makes it both necessary and contentious. Nothing in the physical world tells you what fraction of a refinery’s emissions belongs to petrol rather than diesel; the split depends on the rule you adopt. Because different rules give different answers, allocation is one of the handful of decisions — alongside the system boundary and the functional unit — that most shape a footprint, and one of the few where two careful analysts can legitimately disagree.
For that reason the standards do not leave it open. ISO 14044 sets a strict hierarchy for how to handle it, and a Product Category Rule pins down the exact method for a product category, so that every EPD in that category allocates the same way and stays comparable.
Definition at a glance
| What it is | Dividing a process’s emissions among its several products / functions |
|---|---|
| Triggered by | Multifunctionality — one process, more than one useful output |
| Nature | A modelling choice, not a measurement |
| Governed by | The ISO 14044 hierarchy; fixed per category by a PCR |
| Main methods | System expansion, mass, energy, economic value |
| Why it matters | The method can change a product’s footprint several-fold |
Multifunctionality: What Forces an Allocation
Allocation is only needed when a process is multifunctional — when it delivers more than one valuable output. Three situations produce it, and between them they cover a large share of real industrial systems:
- Co-production. One process yields several products at once — crude oil into fuels and bitumen, a crop into grain and straw, milk into cream and skim, an animal into meat and hides. The shared burden must be split among them.
- Combined outputs. A process delivers two services together — cogeneration (combined heat and power) produces electricity and useful heat from one fuel input, and the fuel’s emissions must be shared between them.
- Recycling and reuse. A material crosses from one product’s life into another’s. The burdens of collection, reprocessing, and the avoided virgin production have to be split between the first life and the second.
If a process makes only one useful thing, there is nothing to allocate — all its burden belongs to that product. The moment a second valuable output appears, the question of who carries the carbon becomes unavoidable.
The ISO 14044 Allocation Hierarchy
ISO 14044 does not simply permit any split — it ranks the options, and requires you to exhaust each level before dropping to the next. This hierarchy is the backbone of every credible allocation decision:
| Step | Approach | What it means |
|---|---|---|
| 1 — Avoid | Subdivision | Split the process into finer sub-processes so each output’s burden is measured directly, and no sharing is needed. |
| 1 — Avoid | System expansion | Expand the boundary to include the co-product’s function, crediting the burden its output displaces elsewhere. |
| 2 — Physical | Partition by physical relationship | Where allocation is unavoidable, split by an underlying physical property — mass, or energy content — that reflects how the burden truly arises. |
| 3 — Other | Partition by another relationship | Where no physical relationship fits, split by another basis — most commonly economic value. |
The logic descends from most to least objective: avoid dividing the burden at all if you can; if you must divide it, use a physical basis that reflects cause; and fall back to value only when physics gives no answer. Skipping straight to the convenient method — usually economic — without testing the steps above it is a common way an assessment loses rigour.
The Allocation Methods
Within that hierarchy, a handful of concrete methods do the work. Each is defensible in the right place and misleading in the wrong one:
| Method | Splits the burden by… | Best when |
|---|---|---|
| System expansion / substitution | Crediting the production displaced by a co-product | Recycling, energy co-products — and the ISO-preferred way to avoid allocation |
| Mass allocation | Each co-product’s share of total mass | Co-products that are physically similar |
| Energy allocation | Each co-product’s share of energy content | Fuels and heat/power, where the function is energy |
| Economic allocation | Each co-product’s share of market value | Co-products that differ greatly in value |
A process emits 1,000 kg CO₂e and yields two co-products: 100 kg of Product A worth £9,000, and 900 kg of Product B worth £1,000.
- Mass allocation: A takes 100 / 1,000 = 10% → 100 kg CO₂e (1.0 kg per kg of A).
- Economic allocation: A takes £9,000 / £10,000 = 90% → 900 kg CO₂e (9.0 kg per kg of A).
Same process, same total emissions — but Product A’s footprint is nine times higher under economic allocation than under mass. Neither is “wrong”; they answer to different logics. This is why the method must be declared, and why comparing two footprints computed on different allocation rules is meaningless. (Figures illustrative.)
Recycling — The Hardest Case
No allocation problem is more argued-over than recycling, because the burdens and benefits of a material’s second life can be assigned to either life. The three broad conventions:
| Convention | Who gets the recycling benefit |
|---|---|
| Cut-off (100:0) | Neither — each life carries only its own burdens; recycled input enters burden-free |
| End-of-life / avoided-burden (0:100) | The first life is credited for the virgin production its recyclate displaces |
| 50:50 and value-corrected | The benefit is shared between the two lives |
The EN 15804 answer is to report the recycling benefit through module D — a system-expansion credit kept beyond the system boundary and never netted into the product’s in-scope total. Galvanised steel’s live module D credit of -1.11 kg CO₂e per kg [GreenCalculus materials.steel.galvanised.module_d · OEKOBAUDAT 2024 · v2026.203] is exactly this: the product is credited for the virgin steel that recycling it will displace. It is an allocation decision made visible — reported openly and separately, so a reader can accept or ignore it, rather than baked silently into the headline figure. The same discipline runs through embodied carbon reporting.
Why Allocation Is Contested
Because allocation is a choice rather than a measurement, it is the part of an LCA most open to honest disagreement — and to quiet manipulation. Shifting from mass to economic allocation, or choosing what a recycled material is assumed to displace, can move a footprint enough to change which of two products looks greener. That sensitivity is why the standards constrain it so tightly:
Two footprints are only comparable if they were allocated the same way. ISO 14044 sets the hierarchy, the GHG Protocol Product Standard and EN 15804 pin down methods for their domains, and a PCR fixes the exact allocation approach for a product category — removing the freedom to pick the flattering method. Whenever you compare two EPDs or footprints, the allocation method is one of the first things to check they share.
Common Confusions
- Confusing allocation with cut-off. Allocation divides a burden among co-products; cut-off excludes minor flows entirely. They are different decisions, both fixed by the PCR.
- Assuming there is one “correct” method. Mass, energy, and economic allocation each answer a different logic. The right choice depends on the process and the standard — and must be declared, not assumed.
- Comparing footprints allocated differently. A mass-allocated and an economically allocated figure for the same product are not comparable, even before any other difference.
- Treating a co-product or byproduct as burden-free. Unless a cut-off convention is deliberately chosen, every valuable output carries a share of the burden — a “waste” that is sold is a co-product.
- Double-counting a system-expansion credit. If both the first and second life claim the same recycling benefit, the saving is counted twice. A credit taken by one product must not be taken by the other.
Frequently Asked Questions
Allocation is the process of dividing the emissions and other burdens of a process among the several products or functions it delivers. It is needed whenever a process is multifunctional — it yields more than one useful output, such as fuels from a refinery, heat and power from cogeneration, or a material and its recyclate — and the shared burden has to be split between them. Allocation is a modelling choice rather than a measurement, which is what makes it both necessary and contested: the method chosen can change a product’s footprint several-fold. ISO 14044 sets a hierarchy for handling it, and a Product Category Rule fixes the exact method for a product category.
Multifunctionality is the situation that forces an allocation: a process delivers more than one valuable output, so its single stream of environmental burden must be shared among them. It arises through co-production (one process yielding several products, like crude oil into petrol, diesel, and bitumen), combined outputs (cogeneration producing both heat and power from one fuel), and recycling (a material passing from one product’s life into another’s). If a process makes only one useful thing, there is no multifunctionality and nothing to allocate — the entire burden belongs to that single product.
ISO 14044 requires allocation to be handled in a set order. First, avoid allocation altogether — either by subdividing the process into finer sub-processes whose burdens can be measured directly, or by expanding the system boundary to include the co-product’s function (system expansion). Second, where allocation cannot be avoided, partition the burden by an underlying physical relationship such as mass or energy content. Third, only where no physical relationship applies, allocate by another relationship — most often economic value. The order runs from most to least objective, and each step must be tested before dropping to the next.
Mass allocation splits a process’s burden according to each co-product’s share of total mass; economic allocation splits it by each co-product’s share of market value. They can give very different results when co-products differ in value. Take a process emitting 1,000 kg CO₂e that yields 100 kg of a product worth £9,000 and 900 kg of a co-product worth £1,000: under mass allocation the valuable product carries just 100 kg CO₂e, but under economic allocation it carries 900 kg — nine times more. Mass allocation suits physically similar co-products; economic allocation is used when values diverge widely, but it moves with prices. Neither is universally correct, which is why the method must be declared and fixed by the applicable standard or PCR.
Recycling is the most contested allocation problem, because the benefit of a material’s second life can be assigned to either life. Three broad conventions exist: cut-off (100:0), where each life carries only its own burdens and recycled input enters burden-free; end-of-life or avoided-burden (0:100), where the first life is credited for the virgin production its recyclate displaces; and shared approaches such as 50:50. EN 15804 reports the recycling benefit as module D, a system-expansion credit kept beyond the system boundary and never netted into the product’s in-scope total — for example galvanised steel’s live module D credit of -1.11 kg CO₂e per kg [GreenCalculus materials.steel.galvanised.module_d]. Keeping it separate lets a reader accept or ignore the credit rather than have it hidden in the headline figure.
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