Timber roof trusses have the lowest climate impact across all measured span lengths when compared to concrete, steel, and glulam options. A study conducted by Zeina Alasadi and Selma Bergström Denizoglu at Chalmers University of Technology, Sweden, shows that nail plate connected timber trusses consistently outperform other materials in reducing CO₂ emissions, even when more timber units are required to match the span coverage of a single truss made from concrete or steel.
The analysis covered trusses with spans from 6 to 26 meters and focused exclusively on emissions from the production phase, using life cycle assessment (LCA) data corresponding to stages A1–A3. The timber trusses were evaluated using verified environmental product declarations (EPDs) from Derome, which supplied design specifications and material volumes. Timber trusses with spans of 6, 8, 12, and 20 meters generated CO₂ emissions of 59.72 kg, 78.5 kg, 145.15 kg, and 352.5 kg respectively when scaled to match standard center distances.
For comparison, a single concrete truss with a 23.14-meter span emitted 3,111 kg CO₂e. Two timber configurations with the same span, one requiring five units and the other ten, emitted 396.10 kg and 651.12 kg CO₂e respectively. In this case, a single concrete truss generated emissions equivalent to nearly 40 timber trusses.
Steel roof trusses showed similarly high emissions. A 12-meter steel truss emitted 841.52 kg CO₂e, whereas five timber trusses of the same effective span emitted only 178.77 kg CO₂e. For a 20.15-meter span, one steel truss released 1,577.85 kg CO₂e, while ten timber trusses covering the same area accounted for just 403.48 kg CO₂e. Even if recycled steel were used, which reduces the emission factor from 1.34 kg CO₂e/kg to 0.663 kg CO₂e/kg, emissions from the 20.15-meter steel truss would still total 780.7 kg CO₂e, nearly double the timber equivalent.
Glulam trusses, though made of wood, showed higher emissions due to the larger wood volumes and partial steel reinforcement. A 25.63-meter glulam truss emitted 2,148.32 kg CO₂e, consisting of 1,798.40 kg from steel components and 349.92 kg from the laminated wood. By contrast, timber alternatives using five trusses of the same span emitted 471.64 kg and 539.34 kg CO₂e depending on construction design.
The study highlights that material selection can drastically affect the overall climate footprint of a building. While timber trusses are typically overlooked for longer spans, the results show they perform efficiently even in industrial applications and large public buildings. With timber solutions reaching free spans of up to 25 meters, and up to 50 meters with interior wall support, they present a scalable option for low-emission construction. Image: Derome
Despite this, concrete, steel, and glulam trusses remain more commonly used in the industry. The report suggests this is due to familiarity, design conventions, and perceived limitations of timber. However, the authors and industry advisors argue that greater awareness of emission differentials could influence earlier project-stage decisions.
