When the measure becomes the target: Goodhart’s law and construction’s carbon numbers

“Goodhart’s law states that when a measure becomes a target, it ceases to be a good measure. I’m not saying that’s what’s happened, but I am asking whether it might be starting to.”

- Alistair Thomas, Associate Director and head of the UK LCA team at Buro Happold

The question has been earned. According to the UK Green Building Council’s Whole Life Carbon Roadmap progress report, built environment emissions have fallen 14% since 2018, against the 24% reduction required by 2024. The UK has never had stronger measurement infrastructure or a denser suite of targets. It is decarbonising at roughly half the required speed anyway. Alistair Thomas built his keynote on interviews with carbon non-experts: the developers, project managers, and contractors whose decisions shape what gets built. What they revealed was not a technical story but a behavioural one.

The symptoms are already visible

Alistair Thomas described contract negotiations in which very knowledgeable people spent significant time arguing whether a target should be 600 or 605 kilograms of CO2 per square metre. In the vast majority of cases, the design never changed; the number moved to absorb missed elements or updated data. He described detailed assessments producing higher carbon values than lazy ones, which quietly rewards being less thorough. He described projects that won sustainability awards on carbon credentials that were not correctly calculated. And he described the most corrosive pattern of all: refurbishment losing to redevelopment on a per-square-metre comparison, purely because a larger new building dilutes its emissions across more floor area while total emissions rise.

“We should be able to celebrate projects that build less, not projects that dilute a bigger number across more floor space.”

- Alistair Thomas, Associate Director and head of the UK LCA team at Buro Happold

Each behaviour is individually rational. Together they amount to what Alistair Thomas called compliance over transformation: hitting the number at the expense of rethinking the system. The pattern has a precedent. BREEAM began as a certification, became a design tool, and is now too often worked backwards from the target through the easiest credits available, which is partly why the Building Research Establishment rewrote its embodied carbon requirements in Version 7. Carbon targets, Alistair Thomas warned, deserve the same vigilance.

Good frameworks, misapplied

None of this is a criticism of the frameworks themselves. The RICS Whole Life Carbon Assessment standard, v2, is among the most comprehensive methodologies in the world, and the UK Net Zero Carbon Buildings Standard gives the industry its first independent, cross-sector definition of net zero performance. Yet frameworks alone won't guarantee how they're applied, as one industry stakeholder told Alistair Thomas in an interview for the keynote:

“The problem lies not in the frameworks or targets themselves, but how they are being implemented by people on projects.”

- Industry stakeholder interviewed for the keynote, quoted by Alistair Thomas

Implementation is where the system leaks. Older benchmarks remain calibrated to the superseded first edition of the RICS methodology, so projects are routinely compared against targets set under a different scope. Assessments arrive with missing elements, misapplied carbon factors, and partial building services coverage. Third-party verification is rare and undefined. Conflicting numbers breed confusion, and confusion breeds inaction: without confidence in the numbers, people will not act on them.

Measure like Part L, verify like NABERS

Alistair Thomas’s structural answer is a two-tier system, modelled on how operational energy is already governed. Part L of the Building Regulations sets a mandatory baseline that every project must meet, while NABERS UK verifies how buildings actually perform for those aiming higher.

Embodied carbon has no equivalent to the first tier. It would be a national baseline methodology with standardised assumptions baked into the reporting tools themselves, simple enough to cut user error and broad enough to reach projects that currently engage with no framework. That is the logic of the industry-proposed Part Z amendment to the Building Regulations, and this is not hypothetical: France’s RE2020 regulation has applied life cycle carbon caps to new buildings nationally since 2022, tightening them on a published schedule.

Embodied carbon's equivalent to the second tier, the UKNZCBS's new verification requirement, hasn't been tested at the scale that NABERS UK has. The second tier is rigorous third-party verification for projects seeking certification, in the way NABERS UK verifies measured energy performance rather than design estimates. Verification needs teeth: defined evidence requirements for key materials, such as concrete pour logs mapped to an Environmental Product Declaration (EPD) and mill certificates for steel. The Government’s Carbon Budget and Growth Delivery Plan already contains its clearest commitment yet to tackling embodied carbon; the architecture Alistair Thomas describes is how that commitment becomes enforceable.

The median project sets the pace

“National carbon performance is set by the median project, not the leading edge.”

- Alistair Thomas, Associate Director and head of the UK LCA team at Buro Happold

The arithmetic is uncomfortable for an industry that celebrates flagships. A 5% embodied carbon reduction applied across the 300,000 homes the UK aims to build each year outweighs a 40% reduction on 50 exemplar schemes. Yet awards, case studies, and conference platforms flow to the frontier while the median project remains barely touched by any framework. Exemplar projects matter because they unlock innovation elsewhere: by naming the barriers, sharing the workarounds, and providing the evidence that de-risks the same decision for the next team. The mass timber insurance playbook exists; most practitioners who cite insurance as the barrier have never heard of it.

“The problem is not that the solutions don’t exist. The problem is that we are not telling the story of how the barriers were overcome well enough for others to follow. The knowledge is there. The reach isn’t.”

- Alistair Thomas, Associate Director and head of the UK LCA team at Buro Happold

Keeping the measure honest

Goodhart’s law is not an argument against carbon targets. It is a warning about what happens when they are applied inappropriately. In that environment, targets become largely irrelevant because performance cannot be compared with confidence. The solution, Alistair Thomas proposes, isn't fewer targets - it's better supported ones:

"The industry has carbon targets; it needs carbon consultancy that focuses on delivering real-world reductions rather than simply reporting numbers."

- Alistair Thomas, Associate Director and head of the UK LCA team at Buro Happold

He concluded that this requires standardised baselines, robust methodologies, verified data, and a culture that asks what a carbon assessment changed on a project, rather than what score it achieved. A target hit with numbers nobody trusts is not decarbonisation. It is carbon accountancy over carbon consultancy.

FAQ

What is Goodhart’s law in construction carbon terms?

Goodhart’s law states that when a measure becomes a target, it ceases to be a good measure. In construction, it appears as carbon numbers negotiated instead of designs changed. Standardised, verified assessment, such as One Click LCA’s framework-aligned tools, keeps the underlying measure reliable.

What is a two-tier carbon compliance system?

It combines a mandatory national baseline methodology with standardised assumptions, as proposed under Part Z and operating in France’s RE2020, with a rigorous third-party verification tier for certified projects. One Click LCA supports both levels, from compliance reporting to verification-ready whole life carbon assessments.

Why can per-square-metre carbon targets mislead?

Intensity metrics reward larger buildings: a bigger redevelopment can show a lower kgCO2e per square metre than a refurbishment while emitting far more in total. Reporting absolute and intensity results together, as One Click LCA does, exposes that distortion before decisions are made.

What is Part Z?

Part Z is an industry-proposed amendment to the UK Building Regulations that would mandate whole life carbon assessment and, over time, cap embodied carbon on major projects. One Click LCA already supports the RICS-aligned methodology on which Part Z is based.