Low carbon starts at concept stage

1 June 2026
In this blog, Craig McFadyen FIStructE, and Jack Brunton MIStructE share their views on how early involvement in concept design lets structural engineers shape form, strategy and material use to cut embodied carbon from the very start.

When discussing embodied carbon reduction in construction, much of the focus is often placed on material specifications during detailed design. However, by the time a project reaches this stage, many of the decisions that will ultimately determine its carbon impact have already been made.
For structural engineers, concept design represents one of the most influential stages in the delivery of lower carbon buildings. Decisions made during the earliest phases of a project can fundamentally affect material quantities, construction methodologies, foundation requirements and long-term building efficiency.

Structural form is a clear example of this influence. Building geometry, span arrangements and grid layouts established during concept design directly affect structural efficiency across the entire project. Longer spans, irregular grids and transfer structures can significantly increase material demand, although in some circumstances these may be justified through reduced column numbers, fewer foundations, improved flexibility or operational requirements. On many projects, these decisions are driven very early by architectural layouts, planning constraints or commercial requirements, often before detailed engineering input has begun. Conversely, rational structural arrangements can often allow substantial reductions in steel tonnage, concrete volumes and foundation loads while also simplifying construction. Similarly, early consideration of basement requirements can substantially influence embodied carbon. Whilst basements are frequently driven by planning, operational or commercial constraints, decisions on their extent, depth, retention strategy, waterproofing and foundation interaction all affect material quantities and construction complexity.

These decisions are rarely made by engineers alone. Lower carbon design is rarely achieved by engineers working in isolation. Collaboration between architects, structural engineers and wider design teams during concept development is essential if projects are to achieve both architectural and sustainability objectives. Early coordination can help align structural efficiency with spatial requirements, services integration and construction constraints before key design decisions become fixed.

The timing of structural involvement is therefore critical. Where engineers are appointed early enough to contribute meaningfully during feasibility and concept development, there is often greater opportunity to influence project outcomes positively. However, where structural input is introduced later in the process, engineers may find themselves working within constraints that significantly limit opportunities for optimisation.
This is particularly relevant when considering embodied carbon. Once building massing, structural zones and planning layouts have been established, many opportunities for material reduction become increasingly difficult to achieve without substantial redesign.

This relationship is illustrated in Figure 1, which demonstrates that the ability to influence embodied carbon is greatest during the earliest project stages, even though the accuracy of assessment increases as design progresses.

Figure 1: Relationship between project stage, assessment accuracy and the ability to influence embodied carbon during design development.

This relationship is increasingly recognised across the industry. The ability to influence embodied carbon is greatest during the earliest project stages, even though the accuracy of carbon assessment increases as design progresses. In practice, this means the most influential carbon decisions are often made before detailed technical design begins.

Concept stage decisions also significantly influence substructure requirements. Reducing structural weight early in the design can have substantial downstream impacts on foundation loads, excavation volumes and below ground concrete quantities. Superstructure weight has a direct relationship with foundation design, meaning efficient framing strategies can reduce not only superstructure material quantities but also excavation volumes, concrete use and associated temporary works below ground.

Early coordination with architects and building services engineers can also help challenge the extent and configuration of below ground construction where appropriate, potentially reducing embodied carbon, excavation impacts and construction complexity. Avoiding unnecessary oversizing is therefore another important consideration, whilst still maintaining appropriate levels of robustness and safety.

Avoiding overdesign is another important consideration. Structural engineers rightly prioritise safety, serviceability and robustness, and member sizing is often governed by factors such as deflection limits, vibration performance, fire requirements, constructability and practical standardisation rather than ultimate strength alone. However, there is increasing recognition that unnecessary conservatism can contribute to avoidable embodied carbon. Efficient engineering is not about reducing safety margins, but about applying engineering judgement appropriately to deliver safe, buildable and materially efficient solutions. Evidence suggests there remains significant scope for material efficiency within structural design. Moynihan and Allwood (2014) found that the average utilisation ratio of steel beams across 23 UK buildings was just 0.40, increasing to 0.48 when weighted by beam length, indicating that many structural elements operate well below their theoretical capacity. This highlights the opportunity for engineers to reduce material demand through efficient structural arrangements and informed engineering judgement without compromising safety or performance.

Importantly, lower carbon design should not be viewed as separate from good engineering practice. In many cases, the principles that improve structural efficiency also improve carbon performance. Rational spans, simpler load paths and coordinated structural layouts can provide benefits across cost, programme, buildability and sustainability.

There is also a clear client benefit. Shifting Paradigms, in a 2023 report based on 72 case studies, found that optimising building design at concept stage achieved an average 41% carbon reduction and a 9% cost reduction. This reinforces the point that early carbon-focused design is not simply an environmental aspiration, but can also support better commercial outcomes.

Client engagement therefore plays a significant role during concept development. Sustainability ambitions are easier to achieve where carbon objectives are embedded within the project brief from the outset. Engineers can help clients understand the wider co-benefits of early decisions, including reduced material extraction, lower biodiversity impact, reduced construction cost and potentially lower planning risk.

This does not mean that every project can prioritise carbon reduction above all other considerations. Structural engineers must still balance commercial pressures, programme constraints, architectural requirements and construction risk. However, early collaboration and informed concept design can significantly improve the industry’s ability to deliver lower carbon outcomes within these constraints.

Specification still has an important role to play, particularly through careful material selection, use of lower carbon concrete mixes and appropriate specification of multi-component cements. On many projects, particularly those involving significant concrete volumes, specification can remain a substantial carbon reduction lever. However, specification alone is not the primary means by which structures are decarbonised. If earlier decisions lead to inefficient grids, excessive spans or unnecessary material quantities, later specification choices may only recover a limited proportion of the carbon already committed.

For structural engineers, the greatest opportunity to influence embodied carbon therefore does not begin at specification stage. It begins during strategic definition, feasibility and concept development, when the fundamental decisions on structural form, grids, spans, load paths, basements and material quantities are still open to challenge.

About the authors

Craig McFadyen chartered engineer and is an Associate Director at AECOM with over 20 years’ experience in structural engineering. He is Vice Chair of IStructE Scotland and has experience across structural design, building warrant certification and multidisciplinary project delivery. Craig is currently undertaking postgraduate studies in Zero Carbon Engineering at Queen’s University Belfast.

Image of a man with a beard in a black suit with blue shirt

Jack Brunton is a chartered civil and structural engineer with 16 years at AECOM, working across a broad range of sectors including healthcare, higher education, rail and heritage. Since October 2023 he has served as Structural Sustainability Lead for AECOM's UK and Ireland Buildings and Places structures practice, responsible for embedding sustainable design across a team of around 160 engineers.