Concrete, steel and timber are often discussed as separate material choices. In practice, they are part of a structural system. The embodied carbon impact of each material depends not only on the material itself, but also on the quantity used, structural efficiency, span, durability, procurement, product data and construction method.

A low carbon structural strategy is rarely as simple as choosing one material and avoiding another. A poorly designed lower carbon material system can still create unnecessary impact. A carefully optimised conventional system may perform better than expected when quantities, spans and specifications are reviewed properly.

The useful question is not only “which material is best?”. It is “which structural approach gives this project the right balance of carbon, performance, durability, cost, compliance and buildability?”.

In Brief

Concrete, steel and timber all need project specific carbon review.

Concrete can be significant because it is often used in large quantities. Steel can be carbon intensive but structurally efficient. Timber can support lower carbon design, but it still needs fire, moisture, durability and sourcing review.

The best structural carbon outcomes usually come from early coordination between architecture, engineering, material specification and embodied carbon assessment.

Structural Carbon

Why structure matters in embodied carbon

The structure of a building can represent a major share of embodied carbon because it often involves large material quantities. Foundations, slabs, columns, beams, cores, reinforcement, framing and structural connections can all influence the result.

Structural decisions also tend to be made early. Once grid, spans, foundations, floor systems and core strategy are fixed, later carbon reductions may become more limited.

This is why embodied carbon review is often most valuable during concept design or design development, before structural decisions are fully locked in.

Concrete

Concrete embodied carbon is shaped by volume and mix design.

Concrete is widely used in Australian buildings because it can provide strength, durability, thermal mass, fire resistance and structural flexibility. It can also contribute significantly to embodied carbon, especially where large volumes are used in slabs, footings, cores, columns and walls.

Concrete carbon reduction may involve reviewing structural efficiency, avoiding unnecessary volume, optimising slab and footing design, considering lower carbon concrete mixes, using supplementary cementitious materials where suitable and checking whether product specific data is available.

Any concrete strategy needs to remain aligned with structural requirements, exposure class, curing, durability, strength gain, construction sequencing and compliance.

Steel

Steel embodied carbon depends on design efficiency and supply chain.

Steel can carry a high carbon intensity, but it can also allow long spans, lighter structures, prefabrication, adaptability and efficient structural performance. The carbon outcome depends heavily on how much steel is used and where it comes from.

Steel related carbon strategies may include optimising member sizes, reducing over specification, reviewing spans and grid layouts, considering recycled content, reusing structural steel where feasible and requesting Environmental Product Declarations or supplier carbon data where available.

The goal is not simply to remove steel. The goal is to avoid unnecessary steel and use it where it gives the project a genuine structural, durability or adaptability benefit.

Timber

Timber can be useful for lower carbon structure, but it is not automatically right for every project.

Timber and engineered timber can help reduce embodied carbon where they replace higher impact materials and are sourced responsibly. Timber may be used in lightweight framing, floor systems, roof structures, engineered timber elements and mass timber systems.

However, timber must still satisfy fire, structural, acoustic, moisture, durability, termite, maintenance, supply chain and construction requirements. It also needs to be considered in relation to building type, climate, detailing and future use.

A timber strategy is strongest when it is integrated early, rather than substituted late into a structure designed around another material system.

Hybrid Systems

Many lower carbon outcomes come from hybrid structural thinking.

In many buildings, the best solution is not purely concrete, purely steel or purely timber. Hybrid systems can use each material where it performs well. For example, a building may use concrete where mass, fire or durability are needed, steel where long spans or connections are useful and timber where lightweight or lower carbon framing is suitable.

Hybrid thinking allows the project team to focus on total system performance rather than material preference. This can be especially important in commercial, education, multi residential and civic buildings where structure, fire, acoustics, services and buildability all interact.

An embodied carbon assessment can help compare options in a way that is project specific rather than theoretical.

Material Efficiency

Reducing unnecessary material is often as important as changing material.

Embodied carbon is affected by both material intensity and quantity. A lower carbon product can still produce a high total impact if it is used in large amounts. A higher intensity material may have a smaller total impact if it is used sparingly and efficiently.

This is why structural optimisation matters. Grid layout, spans, load paths, slab thickness, member sizing, foundation design and repetition can all influence the quantity of material required.

Before looking only at material substitution, project teams should ask whether the structure is using more material than the project actually needs.

Data Quality

Product data can change the result.

Generic assumptions can be useful in early design, but product specific information can improve the reliability of a later stage assessment. Environmental Product Declarations, supplier information, recycled content data and verified product data can all help refine the embodied carbon result.

This is especially important for concrete mixes, steel products, engineered timber, façade systems and prefabricated components where supply chain and product details may materially affect the outcome.

For documentation inputs, read What Information Is Needed for an Embodied Carbon Report?.

Project Type

Residential and commercial projects have different structural carbon patterns.

In residential projects, structural carbon may be shaped by slab design, footings, framing, brickwork, roof structure, retaining walls and extension or renovation decisions. It may also interact with energy performance pathways such as NatHERS, BASIX and Whole of Home.

In commercial projects, structural carbon may be driven by concrete frames, steel systems, long spans, cores, basements, façade support, services coordination and formal pathways such as NABERS Embodied Carbon, Green Star or Life Cycle Assessment.

Design Process

Early coordination is where structural carbon can be reduced most effectively.

Structural carbon is difficult to meaningfully reduce if it is only reviewed at the end of documentation. By then, the grid, spans, floor system, foundations, core strategy and material approach may already be fixed.

Early embodied carbon review can help the design team test structural options, understand carbon hotspots and consider whether changes to material quantities, system choice or specifications are worth exploring.

This does not mean carbon should override every other design priority. It means carbon should be visible early enough to be part of the decision making process.

Avoid Oversimplifying

Concrete, steel and timber should not be ranked without context.

It can be tempting to rank materials from best to worst. That approach is usually too simple. A timber solution may be strong in one building but unsuitable in another. A steel solution may be carbon intensive if overused but efficient where long spans or future adaptability are required. Concrete may have significant embodied carbon but may be necessary for structure, fire, durability or ground conditions.

The right assessment compares realistic options within the actual project constraints.

This is why project specific embodied carbon reporting is more useful than generic material assumptions alone.

Summary

Structural embodied carbon depends on material, quantity and system design.

Concrete, steel and timber can all influence the embodied carbon profile of a building. The impact depends on how much material is used, how it is specified, where it comes from and how it performs within the whole structural system.

The strongest outcomes usually come from early coordination, efficient structural design, reliable product data and a project specific review of realistic material options.

Next Step

Need to understand the structural carbon impact of your project?

Certified Energy can review your project documentation and help identify embodied carbon hotspots across structure, materials, façade systems and construction scope.