The hidden carbon crisis and the emissions no one Is calculating

The construction industry talks confidently about net-zero buildings, life-cycle assessment and low-carbon materials, but we are still only counting half the story. Research suggests that as much as 10 to20% of total project carbon is never formally recorded or reported, hidden in temporary works, untracked transport movements and maintenance cycles that extend decades beyond practical completion. These emissions sit outside most whole-life carbon models, ESG statements and tender frameworks, meaning large parts of a building’s true footprint are missing from the very data we use to measure progress. We cannot reduce what we refuse to quantify and right now, the numbers we are publishing give us a false sense of achievement writes John Ridgeway.

Temporary works are indispensable. Scaffolding, formwork, hoardings, temporary steelwork, site cabins, haul roads and crash decks make construction possible - yet most carbon assessments treat them as if they do not exist. Some studies indicate that temporary works can represent 5 to10% of embodied carbon on a typical project, sometimes more on complex high-rise schemes or heavily scaffolded refurbishments.

Formwork alone can consume thousands of square metres of softwood, plywood or LVL, much of which becomes waste once concrete cures. Site hoardings are frequently replaced two or three times during long programmes. Cabins require lighting, heating, cooling and diesel generators to run. When buildings are modelled, none of it counts, even though the atmosphere pays the bill.

Transport & Logistics

A low-carbon product ceases to be low-carbon if it travels 200 miles more than needed. Transportation is one of the industry’s most underestimated carbon sources, accounting for around one third of construction-phase emissions on major schemes when vehicle movements, idling plant and logistics inefficiencies are included.

Small mistakes scale fast. A wrongly measured façade panel means re-manufacture, re-delivery, re-installation. Poor sequencing may require materials to be transported offsite, stored and then hauled back again. Subcontractors frequently run part-load deliveries instead of consolidated runs. None of this appears in most carbon audits, even though every unnecessary mile is burned into the atmosphere.

Embodied carbon calculations often stop at handover, even though a building may require 30, 50 or even 80 years of maintenance interventions. Replacement roof membrane every 20 years, mechanical plant every 15, emergency remedial works after weathering - all generate emissions, packaging, transport and waste. A façade with half the lifespan of a competitor rarely looks twice as carbon-intensive on paper, because the second, third or fourth replacement cycle is almost never modelled.

There is a widening gap between what we claim to measure and what a building actually emits over its lifetime.

A more honest carbon ledger

If the industry is serious about net zero, then the first step is to acknowledge a simple truth that carbon that goes uncounted does not cease to exist. The sector has become comfortable reporting the emissions that are easy to measure such as concrete poured, steel installed, insulation specified while the carbon tied up in temporary works, logistics inefficiency and post-completion maintenance floats beneath the surface like a submerged mass no one wants to chart. Until we start treating these emissions as real, accountable and reducible, progress remains performative rather than transformative.

A more honest carbon ledger requires a methodology that reflects how projects actually unfold and not how design documents imagine they will. This means expanding whole-life carbon assessments to include temporary structures that may only exist on site for weeks, but require steel, timber, formwork and transport emissions identical to permanent materials. It means tracking how many times materials are moved, not just where they end up. It means acknowledging that an idle excavator burning fuel for three hours contributes just as much carbon as one actively digging. These are not theoretical improvements - they are measurable, trackable and increasingly enabled by digital tools that can monitor deliveries, engine run-time and equipment utilisation in real time.

The carbon equation must also extend beyond practical completion. A building is not a fixed moment in time; it is a 60 to 100-year relationship with maintenance cycles, replacement schedules and eventual disassembly. When materials must be replaced every ten years instead of every thirty, their embodied impact multiplies. When components are installed without consideration for reuse or recovery, the end-of-life emissions merely shift downstream, waiting for someone else to inherit. True carbon accounting follows a building from inception through operation to its final dismantling, capturing the emissions that occur long after ribbon-cutting day.

Net zero cannot be a selective calculation where only the convenient half is visible. The hidden carbon crisis represents not a rounding error but a potential gulf - the gap between buildings that genuinely align with climate legislation and those that only pass the spreadsheet test. If emissions from temporary works, transport waste and maintenance are ignored, we are not solving carbon - we are disguising it.

What we do not count, we cannot reduce. And what we refuse to measure, we cannot claim to control. The next phase of climate progress in construction will not come from new materials or technologies alone, but from better honesty - a willingness to illuminate the emissions that have always been there, quietly unlogged but undeniably real. To build greener, we must first see clearly. It is time to turn the carbon ledger over and write down everything we once left blank.