This article explores the major updates that affect structural engineers working on timber frame designs. It focuses on shear transfer mechanisms, racking wall performance, enhanced connection modelling, and service life provisions.
Timber frames continues to shape modern structural design with its renewability, lightweight strength, and suitability for modular systems. As low-carbon construction grows in importance, engineers must apply codes that reflect contemporary performance standards and real-world behaviour. The second-generation Eurocode 5 introduces this shift, particularly in how it addresses timber-frame buildings.
The 2025 revision of Eurocode 5 Part 1-1 addresses floor diaphragm stiffness, racking resistance, and detailing rules. It brings clarity to areas that previously caused uncertainty among practicing engineers. The updated code now integrates structural behaviour more transparently, especially for floor-to-wall interactions, lateral load paths, and connection performance. It aligns timber design more closely with actual construction practices and engineered product behaviour.
This article explores the major updates that affect structural engineers working on timber frame designs. It focuses on shear transfer mechanisms, racking wall performance, enhanced connection modelling, and service life provisions. This piece aims to guide engineers on how to apply the revised code effectively.
Floor Diaphragm Design
Floor diaphragms play a key role in resisting and distributing lateral loads throughout a structure. In previous versions of Eurocode 5, the role of these diaphragms lacked clarity. Designers often relied on judgement or supplementary literature to model load paths and assess stiffness. This created variability in design outcomes and occasional weaknesses in load transmission.
The 2025 version now addresses this concern directly. It defines floor diaphragms as critical components for transferring wind and seismic loads into racking walls. The code requires engineers to model the diaphragm as a continuous horizontal plane with defined stiffness properties. It treats each component—decking, joists, and sheathing—as part of an integrated system rather than isolated elements.
Shear stiffness of the diaphragm must now reflect both material performance and connection detailing. The code specifies how nailed, screwed, or glued joints influence the diaphragm’s in-plane strength. This helps ensure that the horizontal plane can act reliably under racking loads. Engineers can now avoid underestimating or overestimating diaphragm capacity, both of which compromise safety or economy.
Racking Walls
Racking walls remain the backbone of lateral resistance in timber buildings. The 2025 revision of Eurocode 5 refines how these elements must be assessed and modelled. It introduces more prescriptive guidance for wall-panel arrangements, anchorage requirements, and sheathing connections.
The code now requires engineers to assess the contribution of each sheathed wall panel as part of a system. It accounts for the interaction between vertical studs, horizontal plates, and perimeter fixings. If one part of the wall underperforms, the new rules ensure designers still provide enough stiffness through neighbouring panels or redundant fixings.
Designers must also account for load transfer from upper floors and roofs into racking walls. The new Eurocode insists on continuous shear transfer through all intermediate floor levels. This requirement improves the performance of multi-storey structures where wind and seismic loads increase with height. The updated provisions also help engineers avoid relying too heavily on empirical stiffness values that ignore structural discontinuities.
The standard provides enhanced models for assessing overturning effects at wall bases. It specifies minimum anchor dimensions, layout requirements, and force distribution models. These enhancements aim to reduce the reliance on proprietary solutions or ad-hoc anchor specifications often seen in legacy designs.
Load Path Clarity
One of the most impactful changes in the new Eurocode 5 is its treatment of how floor diaphragms connect to racking walls. The previous standard left this interface open to interpretation. Many designers made conservative or inconsistent assumptions that affected stability and cost.
The updated code defines explicit connection forces between floor edges and the top of supporting walls. It provides equations for calculating shear transfer at these joints, depending on fastener type and spacing. This ensures load paths remain continuous from diaphragm planes into wall studs, then downward to foundations.
Additionally, the code requires that these connections provide resistance against both shear and uplift. This double requirement reflects the true nature of lateral load events. Wind or seismic actions can create both horizontal and vertical reactions, especially in upper floors. By including uplift resistance in diaphragm-to-wall connections, the standard improves overall system robustness.
The revision also aligns the design approach with observed behaviour in real buildings. Past investigations showed that failure often began at these interfaces, not in diaphragms or walls alone. This provision reduces the risk of uncoordinated detailing or overlooked connections.
Enhancing Connection Modelling and Performance
Connection performance in timber structures can greatly influence system strength and ductility. The updated Eurocode 5 introduces clearer categories for different connection types and outlines how to model their stiffness and capacity. It incorporates modern fasteners and jointing systems used in engineered timber products and modular assemblies.
Designers now gain access to tabulated stiffness values for common nail, screw, dowel, and bolt arrangements. The tables reflect both elastic deformation and slip under service loads. They help engineers model real behaviour more accurately in both manual and software-based designs.
For large-scale modular systems, the code includes rules for panel joints and lift-in-place connections. These details account for tolerance, relative movement, and fatigue. The provisions promote repeatable behaviour and help mitigate brittle failure modes often associated with prefabricated elements.
Composite timber-concrete joints also receive attention in the updated code. Although addressed more directly in Eurocode 5 Part 1-3, the guidance supports engineers designing hybrid floor systems. These changes reflect the rise in mass timber construction, where composite elements create greater spans or thinner profiles.
Service Life and Durability Reclassified
Timber’s performance depends on proper protection from moisture, decay, and insect attack. The new Eurocode groups service environments into clearer classes and sets out durability criteria accordingly. It incorporates design life assumptions directly into detailing and material selection processes.
The standard mandates the use of protective detailing in vulnerable areas like wall bases, exposed junctions, and roof edges. Where high humidity or condensation may occur, the code requires either treated timber or additional barrier systems. It also expands on the design responsibilities for interface zones where structural and architectural elements overlap.
Ventilation, drainage, and inspection access now form part of mandatory design checks. These measures ensure that unseen areas—such as cavities behind cladding—do not trap moisture and undermine long-term integrity. This inclusion brings timber design closer to the robust detailing already familiar in masonry and steel construction.
In short, the new durability rules shift the burden from post-construction maintenance to pre-emptive design planning. Engineers must now treat service life performance as an explicit design objective.
Incorporating Modern Timber Products
Eurocode 5 (2025) adapts more effectively to engineered timber products like cross-laminated timber (CLT), laminated veneer lumber (LVL), and glue-laminated timber (glulam). It categorises these materials in ways that improve their structural modelling and simplify code application.
The revised standard provides characteristic values for strength, stiffness, and shrinkage for each product family. Designers can now use default values without referencing external manufacturer data or product-specific approvals. This improves confidence in early-stage design while enabling software tools to apply parameters more consistently.
The code also provides rules for hybrid products and finger-jointed elements. It ensures that joints do not become unrecognised weak points, particularly in tension or vibration-critical areas. This alignment helps engineers design composite systems with reduced reliance on proprietary data.
As the use of mass timber expands, these clarifications simplify how engineers balance material efficiency with performance. They also reduce the need to write project-specific justifications for using modern products that the first-generation code did not mention.
Construction Considerations and Tolerances
The updated Eurocode 5 improves consistency between design models and site practices. It recognises the real-world variability in fastener placement, timber shrinkage, and modular unit fitting. It sets reasonable limits on out-of-plumbness, joint slip, and panel alignment, all of which affect global behaviour.
The code outlines how to treat imperfections in panel layouts and how to adjust for unintended movement or rotation. It allows engineers to accommodate field tolerances without compromising the overall analysis model. These provisions are especially valuable in off-site fabrication and rapid-assembly systems.
It also addresses differential settlement and time-dependent deformations. Engineers must now verify that cumulative deformations remain within serviceability thresholds. This prevents sloping floors, cracking finishes, or misaligned interfaces in long-span systems. The aim is to bridge the gap between calculated behaviour and in-use performance.
Conclusion
The second generation of Eurocode 5 Part 1-1 introduces a more performance-focused and behaviour-driven approach to timber frame design. It enhances modelling rules for floor diaphragms, clarifies racking wall assumptions, and strengthens connection detailing.
Rather than overhaul timber design principles, the second-generation Eurocode refines them. It shifts emphasis toward load paths, verified behaviour, and interface clarity. These updates align structural design more closely with modern fabrication and performance expectations. For practicing engineers, these improvements will make timber structures easier to justify, analyse, and detail with confidence.
Also See: Engineered Wood Products and Timber Construction
Sources & Citations
- Smith, A., & Zajic, M. (2025). Eurocode 5 Part 1-1: What’s new for timber-frame design? The Structural Engineer, Vol. 103 Issue 8.
- Høibø, O.A., & Gauteplass, J. (2024). Performance-Based Timber Engineering. Nordic Wood Journal.
- Frangi, A., & Fontana, M. (2023). Mass Timber Structures: Design, Behaviour, and Fire Safety. Springer.
- British Standards Institution. (2025). EN 1995-1-1: Eurocode 5: Design of Timber Structures – Part 1-1: General – Common rules and rules for buildings. BSI.
