# Our aluminium plant casts billet and extrudes it on one site. Can we report one joint process for the European Union (EU) Carbon Border Adjustment Mechanism (CBAM)?

Canonical: https://senseible.earth/answers/cbam-aluminium-one-joint-process-when-no-billet-sold

Yes, if no intermediate product leaves the site. The Commission's aluminium guide says an installation making goods from both unwrought aluminium and aluminium products may define one joint production process, provided no precursor, such as billet, is sold or otherwise transferred out. Sell billet and you keep two processes.

## The bakery picture

Think of a bakery that makes its own dough and bakes it into bread. If every bit of dough goes into bread, you can count the whole bakery's gas as the bread's. The moment you sell some dough to a neighbour, the dough needs its own count.

Aluminium works the same way. Billet or slab is the dough. Profiles, sheet and wire are the bread. CBAM is the EU's charge on the carbon built into imported goods, and it asks for a figure per tonne for each good.

## The rule in the guide

The guide says installations producing two or more goods from the groups unwrought aluminium or aluminium products may be monitored and reported by defining one joint production process for all those products, provided no intermediate product, meaning a precursor to the second process, is sold or otherwise transferred out of the installation. It marks this as a simplified approach.

## When it does not apply

In the guide's own worked example, 80,000 tonnes of ingot are sold and 120,000 tonnes of slab go into the second process. The guide says a joint process, which it calls the bubble approach, is not possible there, so it keeps two production processes and passes the slab figure into the second one as a precursor, scaled by a mass ratio.

## Both routes agree when nothing is sold (our reading)

Our reading, from the algebra of the example below: the same answer comes from the joint process and from two linked processes. The joint route just saves the second set of workings.

Separate from this, the Commission's Questions and Answers document says Combined Nomenclature (CN) codes of the same group have to be grouped under one process when they differ only in size or shape and use the same precursors in the same types, quantities and proportions.

## A billet caster and extruder (example)

- Casthouse: 900 tonnes of carbon dioxide (CO2) for 5,000 tonnes of billet, all extruded. Extrusion furnaces: 500 tonnes for 4,800 tonnes of profile
- Joint process: (900 + 500) / 4,800 = 0.2917, about 0.292 tonnes per tonne of profile
- Two linked processes: billet 900 / 5,000 = 0.18 per tonne. Mass ratio 5,000 / 4,800 = 1.0417. 0.18 x 1.0417 = 0.1875, plus extrusion 500 / 4,800 = 0.1042. Total 0.2917
- Now suppose the casthouse makes 6,000 tonnes at the same 0.18 per tonne (1,080 tonnes) and sells 1,000 tonnes of billet. No joint process is allowed. The sold billet carries 0.18 tonnes per tonne from the first process alone

All figures are example numbers. The mass ratio is tonnes of billet used per tonne of profile made, as in the guide's example.

## What Senseible does here

Senseible reads fuel invoices and electricity bills into monthly records. Deciding how your CN codes group into processes is custom, on request. Senseible builds the verifier-ready file and checks every figure in-house; an accredited verifier Senseible partners with signs it off, or the client sends it to their own.

- [Build your aluminium CBAM file](https://senseible.earth/cbam-suite)
- [Aluminium sheet worked example](https://senseible.earth/answers/cbam-aluminium-sheet-worked-example)
- [Own precursor made in the same plant (steel)](https://senseible.earth/answers/cbam-own-precursor-made-in-same-installation)
- [Alloy grades and one figure per CN code](https://senseible.earth/answers/cbam-alloy-grades-one-figure-per-cn-code)

Sources: [European Commission, CBAM Guidance No. 5e, aluminium (14 August 2026)](https://taxation-customs.ec.europa.eu/document/download/590e983b-c937-41ea-bb9f-810c29e70e1e_en?filename=Guidance%20No.%205e%20-%20Sector-specific%20guidance%20document%20on%20aluminium.pdf), [European Commission, CBAM Questions and Answers](https://taxation-customs.ec.europa.eu/document/download/013fa763-5dce-4726-a204-69fec04d5ce2_en?filename=CBAM_Questions%20and%20Answers.pdf)

Last reviewed 2026-11-07. Check section 3.1.2 of the guide and Annex II, point A.4 of Implementing Regulation (EU) 2025/2547 before you choose a joint process. The guide says it is not legally binding.