As the construction industry looks for ways to cut emissions, the choice of structural materials is under greater scrutiny than ever. Buildings account for a significant share of global carbon output, not only through their energy use but also through the materials that go into them. Two of the most common options for structural frames – engineered timber and steel – offer different advantages, but their embodied carbon profiles reveal a striking contrast.
Embodied carbon refers to the greenhouse gas emissions generated during the extraction, manufacture, transport and installation of a material. Steel is strong, versatile and fully recyclable, but producing it is energy intensive. The blast furnace process requires high temperatures and significant amounts of fossil fuel, which result in substantial carbon emissions before a single beam reaches a construction site.
Engineered timber, on the other hand, starts with a renewable resource: wood. Products such as cross-laminated timber (CLT) and laminated veneer lumber (LVL) are created by bonding layers of timber to achieve high strength and dimensional stability. Because trees absorb carbon dioxide as they grow, the carbon stored in timber products offsets part of the emissions generated during processing. When sourced from responsibly managed forests, engineered timber can even act as a long-term carbon sink throughout the life of a building, mentioned on Gov.uk.
Comparisons between the two materials show clear differences. A tonne of structural steel typically carries several times the embodied carbon of an equivalent volume of engineered timber. While recycled steel can reduce these numbers, timber’s ability to lock away carbon gives it a significant advantage in most life-cycle assessments. In addition, timber components are lighter, which can lower the emissions from transport and reduce the amount of concrete needed for foundations.
This does not mean that timber is the automatic choice for every project. Steel remains essential for certain spans, loads and fire performance requirements, and it offers unrivalled recyclability at end of life. Many modern buildings combine the two materials to balance strength, design flexibility and sustainability. The key is to understand the carbon implications early in the design process and specify materials accordingly.
Suppliers such as Harlow Bros Timber Merchants provide engineered timber solutions for a wide range of projects, helping designers and contractors explore lower-carbon options without compromising on performance. Their work demonstrates how careful sourcing and product selection can reduce embodied emissions while maintaining structural integrity.
For architects, engineers and developers aiming to meet net-zero targets, evaluating embodied carbon is no longer optional. Whether a project calls for a full timber frame, a hybrid system or a carefully optimised steel structure, material decisions made today will shape the carbon footprint of buildings for decades to come. Choosing engineered timber where appropriate is one of the most effective ways to deliver immediate carbon savings and contribute to a more sustainable built environment.
