Scope 3 Double Counting: The Same Tonne of Concrete, Counted Twice
Head contractors are quietly counting the same concrete and the same subcontractor diesel two and three times inside a single inventory. Across companies that overlap is by design. Inside your own ledger it is an error, and AASB S2 makes it more likely, not less. Here is where it happens and how to draw a boundary that survives assurance.
Open the emissions ledger of any Australian head contractor mid-project and search for the concrete on a single pour. There is a decent chance you find it twice.
Once as a batch plant delivery docket. Forty-two cubic metres of N32, matched to a supplier EPD, sitting in Scope 3 Category 1 as purchased goods. And again inside the concreting subcontractor's progress claim, which someone classified as purchased services and ran through a spend-based factor because unbundling the labour from the material was going to take a week nobody had.
Same pour. Same truck. Two entries. Each one defensible on its own. Together they are wrong.
This is the failure mode that Scope 3 conversations skip past. Fuel dockets get all the attention because they are the easy case: one fuel, one unit, one factor, unambiguously Scope 1. Nobody double counts a litre of diesel from a Caltex docket. But the moment you move into the value chain, the boundaries stop being physical and start being contractual, and contracts overlap in ways that emissions categories were never designed to handle.
Treasury has a consultation open right now, from 24 August to 2 October 2026, called Improving the efficiency of climate-related financial disclosures. One of the things it asks about is where the boundary of a reasonable value-chain information request should sit. That question is live because Group 1 entities have hit their second reporting year, Scope 3 is now on the table, and the practical answer turns out to be much harder than anyone drafting the standard expected.
The double counting everybody talks about is the one that matters least
Ask most sustainability leads about Scope 3 double counting and you get the value-chain version. The cement producer burns the clinker and reports it as Scope 1. The concrete supplier buys the cement and reports it as Category 1. You buy the concrete and report it as Category 1. Your client buys the building and reports it as Category 2. One tonne of process emissions, four separate inventories.
That overlap is intentional. The GHG Protocol built the three scopes that way on purpose, so that every business with any influence over an emission source can see it in their own numbers and act on it. Aggregate every corporate inventory in Australia and you would get a number several times larger than the national inventory. That is a known property of the framework.
The version that will get you in trouble is different, and it sits entirely inside your own boundary. A Scope 3 inventory does not include anything you have already reported as your own Scope 1 or Scope 2. The fifteen categories are meant to be mutually exclusive. Where a purchase genuinely could sit in two categories, the GHG Protocol's own Scope 3 guidance leaves the classification to you but is clear that you must not count it in both, and that if overlap inside your inventory turns out to be unavoidable you have to explain it in the disclosure.
Very few Australian reporters explain it, mostly because nobody has gone looking.
AASB S2 makes this harder, and it did so deliberately
The GHG Protocol Corporate Value Chain Standard sets a minimum boundary for each of the fifteen categories. For Category 1, that minimum is the cradle-to-gate Scope 1 and Scope 2 emissions of your suppliers. Stop there and you have met the GHG Protocol.
You have not met AASB S2. The AASB's own educational material on greenhouse gas disclosure, published August 2025, puts the question directly and answers it flatly: an entity applying AASB S2 cannot limit its measurement and disclosure of Scope 3 emissions on the basis of the minimum boundaries in the Value Chain Standard. Paragraph B32 requires you to consider all fifteen categories against your business model. Paragraph B36 requires you to determine the breadth and composition of your value chain using all reasonable and supportable information available without undue cost or effort. For Australian construction, that means the standard is pushing you upstream past your immediate supplier, into territory that your other categories may already be covering.
Then paragraph B40 pushes in the same direction from a different angle. The Scope 3 measurement framework tells you to prioritise inputs based on direct measurement, data from specific activities in your value chain, timely data that faithfully represents the jurisdiction and technology involved, and data that has been verified. Every time you take that seriously and replace a spend-based line with real activity data, you create a fresh opportunity to count something that another line already contains.
Better data and more overlap arrive together. So fix the boundaries first, before you start improving the data sitting inside them.
Three places it actually happens on a construction project
The first is supply-and-install, and it is the biggest one.
Consider a commercial job in Brisbane with a $2.1 million concreting subcontract covering supply, place, finish and cure. On a package like that, material typically runs somewhere between 55% and 70% of the contract value depending on the mix and the pour complexity. Run the whole $2.1 million through an economic input-output factor for construction services and the concrete is inside that number, because the ANZSIC-level factor is built from an economy where concreting firms buy concrete.
Meanwhile site admin has been filing batch plant dockets all quarter. Say 3,400 cubic metres of N32, matched at roughly 300 kg CO2-e per cubic metre from the supplier's EPD, which gives you about 1,020 tonnes in Category 1 from the material side. Both entries are in the ledger. Most of that 1,020 tonnes is also sitting inside the spend line, and nothing in a spreadsheet will tell you so.
The second is subcontractor fuel burnt on a site you control, and it crosses frameworks.
Under section 11 of the NGER Act, operational control determines who reports. The Clean Energy Regulator's contracts and leasing guideline is unambiguous that when you estimate emissions for a facility under your control you must include the activities of contractors and subcontractors at that facility. The excavator burning 25 litres an hour on your site belongs in your NGER report as Scope 1, regardless of who owns the machine.
Which means, by the GHG Protocol's own rule, it cannot also be in your Scope 3. But if you spend-based the earthworks subcontract, that fuel is baked into the factor. Now the same litre appears twice, in two frameworks, under two sets of global warming potentials, since NGER runs on AR5 and AASB S2 requires AR6 outside the jurisdictional relief in AASB 2025-1. We have written separately about running NGER and AASB S2 off one dataset, and this is the specific reconciliation that breaks first.
The third is the joint venture, where the overlap goes vertical.
An infrastructure JV keeps a project-level ledger at 100%. Each parent then picks up its share under whichever consolidation method it has chosen, and those methods often differ between partners. If one of those parents is also the head contractor delivering the works, its own Category 1 may carry the project services as a purchase, on top of the share it already consolidated. Paragraph 29(a)(iv) of AASB S2 requires you to disaggregate Scope 1 and Scope 2 between the consolidated accounting group and investees excluded from it, and paragraph B27 requires you to disclose which measurement approach you picked and why. Those two disclosures are exactly where the overlap becomes visible to an auditor. We covered the mechanics of the consolidation choice in joint venture emissions allocation.
Plant hire deserves a sentence of its own. Dry hire, where you supply the operator and fill from your own site bowser, puts the fuel squarely in your Scope 1 while the hire invoice sits in Category 1 as a service. Wet hire, where the operator comes with the machine, usually leaves the fuel in your Scope 1 anyway because the activity is on your controlled facility. The hire invoice is still a service. It is the fuel that must not be counted on both sides.
| Activity | Where it belongs, once | Where it gets picked up a second time |
|---|---|---|
| Subcontractor plant diesel on your controlled site | Your Scope 1, in the NGER facility report | Inside a spend-based Category 1 line on the subcontract |
| Concrete under a supply-and-install package | Category 1, from either the docket or the contract value | Batch plant dockets and the sub's progress claim, both |
| Wet-hire plant with operator | Fuel in Scope 1, hire fee in Category 1 | Fuel again inside the hire invoice spend factor |
| Delivered-price material | Category 1, transport included in the price | Category 4, re-estimated from distance and mode |
| JV project works where you are also head contractor | Your consolidated share, per your chosen method | Category 1 as purchased services from the JV entity |
| Subcontractor depot power and workshop gas | Your Category 1 | Almost never counted at all |
The last row is the interesting one. The same reporting teams double counting site diesel are usually missing the subcontractor's off-site footprint entirely. Overstatement and understatement happily coexist in the same inventory.
The rule that clears most of it
Start with geography and control, because that boundary is the sharpest one available and it is written into legislation rather than left to judgement.
If the activity happened at a facility under your operational control, it is your Scope 1 or Scope 2 and it must be excluded from Scope 3. If it happened somewhere else, at the subcontractor's depot, in their workshop, in their utes travelling between jobs, it is your Category 1. Same subcontractor, both sides of the line, and the line is the site gate. Getting this one right resolves more double counting than any other single decision.
Then handle the contractual overlap by naming an owner. For each supply-and-install package, decide whether the material is captured from delivery dockets or from the contract value. Write the decision into your basis of preparation, apply it for the life of the contract, and do not change it mid-year without a restatement note. If you have good dockets, use the dockets and treat the subcontract as labour only by stripping the material portion from the spend line. If you do not, use the contract value and switch the dockets off. Either is defensible. Doing both is not.
Freight is the easy one to close out. If your supplier quotes a delivered price, the transport is inside your Category 1 figure and you should say so rather than separately estimating Category 4 from distances. The category boundary question comes up in most inventories and the fix is to write down a convention and hold to it.
What we have not solved, and want to be straight about: nominated supplier arrangements. Head contractor negotiates a rate directly with a concrete supplier, the subcontractor draws against it, the docket comes to you and the invoice goes to them. Both parties have a legitimate claim to the material. We do not think there is a clean answer here yet beyond agreeing it in the subcontract and documenting the treatment. We are also not confident the one-owner-per-package rule holds its shape past a few hundred concurrent subcontracts without real coding discipline at accounts payable, and that discipline is not something software can impose on its own.
Making the overlap visible before your auditor does
Under ASSA 5010, a limited assurance provider will trace a sample of emission records back to source. If two records trace to documents describing the same physical activity, that is a finding.
The reason double counting survives so long in construction is that spreadsheets do not carry provenance. A row of numbers cannot tell you which document produced it, so nobody can ask the question that would catch it: is this tonne already somewhere else in this file?
Carbonly was designed around that question. Every emission record carries its source document, so a record is always traceable back to the docket, invoice or claim it came from. The seven-year audit trail keeps content fingerprints, which catches the literal duplicate, the same PDF arriving once by project email and once through a SharePoint folder sync, a pattern we go into in more detail in duplicate invoices inflating carbon numbers. Anomaly detection runs across the ledger and flags the shape of an overlap: a material quantity appearing twice in a period, a spend line and an activity line moving together. Period locking means a boundary correction lands as a restatement with a reason attached, and a closed quarter cannot be quietly edited afterwards. JV consolidation runs under operational control, financial control and equity share off one set of records, so the project ledger and each partner's share are the same underlying data rather than three spreadsheets that will eventually disagree. And the AR5 and AR6 toggle applies at report render time, so your NGER submission and your AASB S2 disclosure draw from the same litres of diesel rather than two parallel models.
What the software cannot do is decide your boundary. It can surface a suspected overlap and show you both source documents side by side. Whether the concrete belongs to the docket or the subcontract is a judgement your preparer and your assurance provider need to agree on, and if a consultant is leading your engagement they should be the ones making that call. Carbonly is the workshop equipment. Someone still has to be the craftsperson.
None of this is construction-only, either. Property and REIT portfolios hit it on tenant fit-out works. Mining hits it with contract mining fleets running on operator-controlled sites. Manufacturing hits it with tolling arrangements where the material never changes hands. Logistics hits it with subcontracted linehaul, and councils and health services hit it with managed facilities contracts. Construction is just where the contracts overlap most densely and the material volumes are large enough that a duplicate moves the headline number.
Pick your ten largest supply-and-install subcontracts from last quarter. For each one, check whether the material also arrived as a delivery docket in the same period. If the answer is yes on more than two of them, your Category 1 is overstated and you do not currently know by how much. That is worth finding out before your assurance provider does, and before Treasury's consultation closes on 2 October.
Related Reading:
- Subcontractor Emissions: The Scope 3 Data Gap in Australian Construction - What activity data you can actually pull from procurement documents you already hold
- Joint Venture Emissions Allocation - Operational control versus equity share, and why partners disagree
- NGER vs AASB S2: Running Dual Frameworks Without Doubling Your Team - One dataset, two frameworks, two sets of GWP values
- The 15 Scope 3 Categories: Which Ones Actually Matter - Category screening and where the boundaries blur
- Concrete: The Hardest Line Item in Australian Scope 3 - Once you know the tonne is yours, picking the right factor for it is its own problem