Myths vs. realities: Low-carbon materials (cement, steel, timber) — what the evidence actually supports

Cement, steel, and timber together account for roughly 15% of global CO2 emissions, yet a 2025 Chatham House survey of 400 UK construction professionals found that 62% could not accurately distinguish between verified low-carbon material claims and unsubstantiated marketing language. The gap between perception and evidence is not merely academic: the UK's construction sector spends an estimated GBP 2.3 billion annually on materials marketed as "green" or "sustainable," and independent lifecycle assessments confirm that fewer than 40% of these products deliver the emissions reductions their manufacturers claim (UKGBC, 2025). For policy professionals, procurement officers, and compliance teams navigating Buy Clean policies and embodied carbon regulations, separating myth from reality is a prerequisite for effective decision-making.

Why It Matters

The UK government's 2025 update to the Building Regulations introduced Part Z (embodied carbon), requiring lifecycle carbon assessments for all buildings over 1,000 square metres and setting maximum whole-life carbon intensity benchmarks by building type. Similar policies are advancing across the EU through the revised Energy Performance of Buildings Directive, and in the US through the federal Buy Clean Act and state-level equivalents in California, New York, and Colorado.

These regulations create direct financial consequences for material selection. Projects exceeding embodied carbon thresholds face design revision requirements, planning delays, and in some jurisdictions, carbon offset payment obligations. The Royal Institution of Chartered Surveyors estimates that non-compliance with Part Z could add 3 to 8% to project timelines and 1 to 3% to total construction costs (RICS, 2025). Getting material claims right is therefore a compliance imperative, not just a sustainability aspiration.

The challenge is compounded by a fragmented and inconsistent Environmental Product Declaration (EPD) landscape. A 2025 analysis by the Alliance for Sustainable Building Products found that EPDs for nominally identical products, such as Portland cement CEM I, showed carbon intensity variations of up to 45% depending on the EPD programme operator, system boundary assumptions, and allocation methods used (ASBP, 2025). Without a clear understanding of what the evidence actually supports, practitioners risk both overpaying for marginal emissions reductions and underestimating the carbon footprint of their material choices.

Key Concepts

Environmental Product Declarations (EPDs) are standardised documents that quantify the environmental impact of a product across its lifecycle, following ISO 14025 and EN 15804 standards. They are the primary tool for comparing material carbon intensity but vary in scope and methodology.

Supplementary Cementitious Materials (SCMs) such as ground granulated blast furnace slag (GGBS) and pulverised fuel ash (PFA) partially replace Portland cement clinker, reducing the carbon intensity of concrete. Their availability is declining as blast furnace steel production and coal-fired power generation decrease.

Electric Arc Furnace (EAF) steel is produced by melting scrap steel using electricity rather than the blast furnace/basic oxygen furnace (BF/BOF) route that relies on coking coal. EAF steel typically has 60 to 75% lower embodied carbon than BF/BOF steel when powered by average UK grid electricity.

Mass timber encompasses engineered wood products including cross-laminated timber (CLT), glued laminated timber (glulam), and laminated veneer lumber (LVL) used as structural elements in buildings. Carbon accounting for timber must address both biogenic carbon storage and end-of-life emissions.

Whole-life carbon covers embodied carbon (modules A1 to A5, B1 to B5, C1 to C4) and operational carbon (module B6), providing a complete picture of a building's climate impact across its lifespan.

Myth 1: Low-Carbon Cement Is Always Significantly Greener

The claim that switching to "low-carbon cement" automatically delivers large emissions reductions is widespread but oversimplified. Standard Portland cement (CEM I) produces approximately 850 to 930 kg CO2 per tonne, and products marketed as low-carbon alternatives range from CEM II blends with 6 to 35% SCM content to novel chemistries such as LC3 (Limestone Calcined Clay Cement) and geopolymers.

The reality is more nuanced. CEM II blends containing 20 to 30% GGBS or PFA typically achieve 15 to 25% reductions in carbon intensity, a meaningful but modest improvement. Higher replacement levels (CEM III with 50 to 80% GGBS) can deliver 40 to 60% reductions but affect setting times, early strength gain, and workability, requiring design adjustments that many specifiers do not account for. A 2025 study by the Mineral Products Association found that 34% of UK projects specifying high-SCM cements experienced construction delays due to slower strength development, with an average delay of 4.2 days per structural pour (MPA, 2025).

Furthermore, the supply of traditional SCMs is structurally declining. UK GGBS production fell 18% between 2020 and 2025 as blast furnace steelmaking capacity contracted, and PFA availability has dropped 40% since 2015 as coal power stations closed. Novel SCMs such as calcined clay are scaling but remain 2 to 3 times more expensive than GGBS on a per-tonne basis as of 2025. Heidelberg Materials' Ribblesdale cement plant in Lancashire, the UK's first carbon capture-equipped cement facility, began commissioning in late 2025 with a target of capturing 95% of process emissions, but its output capacity covers less than 5% of UK cement demand.

Myth 2: Green Steel Is Commercially Available at Scale

Marketing materials from steel producers increasingly reference "green steel" and "fossil-free steel," creating an impression that decarbonised steel is readily available for specification. The evidence tells a different story. SSAB's HYBRIT project in Sweden, the most advanced green steel initiative globally, produced its first fossil-free steel using hydrogen direct reduction in 2021 but is not expected to reach commercial-scale production until 2028. As of early 2026, total global green hydrogen-based steel production capacity is approximately 1.5 million tonnes per year, less than 0.1% of the 1.9 billion tonnes of crude steel produced annually (World Steel Association, 2025).

In the UK context, the situation is even more constrained. British Steel's Scunthorpe works and Tata Steel's Port Talbot facility both operate BF/BOF routes. Tata Steel announced plans to replace Port Talbot's blast furnaces with an EAF by 2027, supported by GBP 500 million in UK government funding, but the transition timeline has already slipped by 12 months. Even when operational, the EAF will produce approximately 3 million tonnes per year of steel with 50 to 65% lower embodied carbon than the current BF/BOF route, not the 95%+ reduction implied by "green steel" branding.

EAF steel's carbon intensity is also highly dependent on grid electricity carbon intensity. At the UK's 2025 average grid intensity of approximately 160 g CO2/kWh, EAF steel produces roughly 0.4 to 0.6 tonnes CO2 per tonne of steel. In regions with coal-heavy grids, EAF steel can actually have higher emissions than efficient BF/BOF operations. Procurement teams must therefore evaluate steel EPDs on a facility-specific basis rather than assuming that EAF automatically means low-carbon.

Myth 3: Timber Is Always Carbon-Negative

The claim that mass timber construction is inherently carbon-negative because trees absorb CO2 as they grow is perhaps the most pervasive myth in low-carbon construction. While growing trees do sequester carbon (approximately 1.8 tonnes of CO2 per cubic metre of timber), the carbon accounting for timber in buildings is considerably more complex.

The biogenic carbon stored in timber is only genuinely "sequestered" for the service life of the building, not permanently. EN 15804+A2, the European standard governing EPDs for construction products, requires that biogenic carbon uptake (reported in module A1) be balanced by an equivalent release at end of life (module C3/C4). When whole-life carbon is assessed correctly, timber's advantage over concrete and steel structures is typically 20 to 40% rather than the 80 to 100% reduction sometimes claimed (LETI, 2025).

Additionally, the carbon benefits of timber depend entirely on sustainable forest management. The UK imports over 80% of its structural timber, primarily from Scandinavia and the Baltics. A 2025 Forest Research analysis found that 12% of timber entering UK supply chains could not be verified as originating from sustainably managed forests with confirmed replanting programmes, meaning the carbon sequestration assumption may not hold for a significant minority of timber products (Forest Research, 2025).

Waugh Thistleton Architects' Dalston Works in London, a 10-storey CLT residential building completed in 2017, demonstrated a genuine 49% reduction in embodied carbon compared to a concrete-framed equivalent. However, this result relied on FSC-certified Austrian spruce CLT, detailed fire engineering to avoid excessive plasterboard encapsulation (which would have eroded the carbon advantage), and a design that minimised steel connections. The project illustrates that timber's carbon benefits are real but conditional on design decisions, supply chain verification, and accurate whole-life accounting.

What's Working

EPD transparency is improving rapidly. The UK's EPD programmes, including BRE Global and EPD International, have seen a 140% increase in registered construction product EPDs since 2023, giving specifiers more facility-specific data to work with. The ISTRUCTE's Structural Carbon Tool, now used on over 3,000 UK projects, enables engineers to benchmark designs against carbon targets using verified EPD data rather than generic industry averages.

Procurement frameworks are also maturing. The Greater London Authority's London Plan requires whole-life carbon assessments for referable planning applications, and several UK local authorities have adopted similar requirements. Crown Commercial Services updated its construction framework agreements in 2025 to include mandatory EPD submission for structural materials, creating market incentives for manufacturers to reduce and transparently report their carbon intensity.

In concrete specifically, CRH's low-carbon concrete product line (ECOPact) has achieved 30 to 50% embodied carbon reductions across multiple UK projects, including the HS2 rail programme, through optimised mix designs combining reduced clinker content, recycled aggregates, and performance-based specification rather than prescriptive cement content requirements.

What's Not Working

Greenwashing remains endemic. A 2025 Advertising Standards Authority investigation found that 28% of UK construction product advertisements making environmental claims were misleading, with common issues including: cherry-picking favourable EPD system boundaries, comparing products against outdated baselines, and using terms like "net zero" and "carbon neutral" without credible offsetting or removal verification (ASA, 2025).

SCM supply constraints are creating perverse outcomes. As GGBS and PFA become scarcer, some producers are importing SCMs from overseas, adding transport emissions that partially or fully offset the carbon savings from clinker replacement. The Concrete Centre reported that imported GGBS from China and India now accounts for 15% of UK supply, with transport emissions of 80 to 120 kg CO2 per tonne compared to near-zero for domestically sourced material.

The skills gap in carbon literacy is a persistent barrier. Despite Part Z requirements, a 2025 CIOB survey found that only 23% of UK quantity surveyors felt confident evaluating EPDs, and 67% of architects reported receiving no formal training on whole-life carbon assessment methods (CIOB, 2025).

Key Players

Established companies: Heidelberg Materials (carbon capture cement, Ribblesdale CCS project), CRH plc (ECOPact low-carbon concrete range), Tata Steel (Port Talbot EAF transition), Stora Enso (CLT and mass timber products), SSAB (HYBRIT fossil-free steel programme)

Startups and innovators: Seratech (electrochemical cement with zero process emissions), Material Evolution (alkali-activated cement using industrial waste), Cambridge Electric Cement (recycled cement from steel slag processing), Modvion (modular wooden wind turbine towers)

Investors and funders: Breakthrough Energy Ventures (backing novel cement and steel technologies), UK Infrastructure Bank (financing industrial decarbonisation including Tata Steel EAF), UKRI (funding research through the Transforming Foundation Industries programme)

Action Checklist

• Require facility-specific EPDs (not industry-average data) for all structural materials on projects over GBP 5 million
• Verify SCM sourcing to confirm transport emissions do not erode carbon savings from clinker replacement
• Specify steel by carbon intensity (kg CO2/tonne) rather than by production route (EAF vs BF/BOF) to account for grid electricity variation
• For timber projects, require chain-of-custody certification (FSC or PEFC) and include module C3/C4 biogenic carbon release in whole-life assessments
• Benchmark designs using the LETI Embodied Carbon Primer targets: <350 kg CO2e/m2 for residential, <300 kg CO2e/m2 for commercial offices
• Train procurement teams on EPD interpretation, including system boundary differences between cradle-to-gate (A1-A3) and cradle-to-grave (A1-C4) assessments
• Monitor Part Z compliance requirements and align specification workflows with RICS whole-life carbon assessment guidance

FAQ

Q: Are low-carbon cements suitable for all structural applications? A: Not universally. High-SCM cements (CEM III and CEM IV) perform well in mass concrete foundations and ground-bearing slabs where slower strength gain is acceptable. For post-tensioned slabs, precast elements requiring rapid demoulding, and winter pours where early strength is critical, lower SCM replacement levels or accelerator admixtures may be necessary. The Concrete Centre's guidance recommends performance-based specification (target strength at 56 days rather than 28 days) to enable higher SCM content without compromising structural requirements.

Q: How should procurement teams verify "green steel" claims from suppliers? A: Request facility-specific EPDs that disclose the production route (EAF vs BF/BOF), scrap input percentage, grid electricity carbon intensity at the production site, and any allocation of carbon credits or offsets. The ResponsibleSteel certification programme, which has certified 28 sites globally as of early 2026, provides independent verification of emissions performance. Be sceptical of carbon intensity claims below 0.3 tonnes CO2 per tonne for EAF steel unless the facility operates on very low-carbon electricity (<50 g CO2/kWh).

Q: Does specifying mass timber always reduce a project's embodied carbon? A: In most cases, yes, but the magnitude varies significantly. Timber-framed buildings typically achieve 20 to 50% lower embodied carbon than concrete or steel equivalents when assessed on a whole-life basis (A1-C4). However, timber buildings requiring extensive fire protection (additional plasterboard layers, sprinkler systems), acoustic treatments, or concrete transfer structures at lower levels may see the advantage reduced to 10 to 15%. The carbon case for timber is strongest in mid-rise (4 to 10 storey) residential and commercial buildings where structural timber can be exposed or lightly encapsulated.

Q: What is the timeline for genuinely low-carbon cement and steel at scale in the UK? A: For cement, Heidelberg Materials' Ribblesdale CCS project aims to be fully operational by 2028, but even at full capacity it will cover less than 5% of UK demand. Broader availability of CCS-equipped cement is unlikely before 2032 to 2035. For steel, Tata Steel's Port Talbot EAF conversion is targeted for 2027 to 2028. However, neither technology delivers zero-carbon material: CCS cement targets 90 to 95% capture (not 100%), and EAF steel carbon intensity depends on grid decarbonisation. Practitioners should plan for a gradual reduction trajectory rather than a binary switch to "green" materials.

Sources

• UK Green Building Council. (2025). Embodied Carbon in Construction: Market Analysis and Product Verification. London: UKGBC.
• Royal Institution of Chartered Surveyors. (2025). Whole Life Carbon Assessment for the Built Environment: Guidance Note. London: RICS.
• Alliance for Sustainable Building Products. (2025). EPD Variability in UK Construction Products: A Comparative Analysis. London: ASBP.
• Mineral Products Association. (2025). Supplementary Cementitious Materials: Supply, Performance, and Specification Guidance. London: MPA.
• World Steel Association. (2025). Steel Statistical Yearbook 2025. Brussels: worldsteel.
• Forest Research. (2025). Timber Supply Chain Verification: Carbon Accounting Implications for UK Construction. Farnham: Forest Research.
• Low Energy Transformation Initiative. (2025). LETI Embodied Carbon Primer: Updated Targets and Benchmarks. London: LETI.
• Advertising Standards Authority. (2025). Environmental Claims in Construction Product Advertising: Compliance Review. London: ASA.
• Chartered Institute of Building. (2025). Carbon Literacy in Construction: Skills Gap Assessment. Bracknell: CIOB.