Every structural timber building in the UK, from a domestic loft conversion to a multi-storey cross-laminated timber block, is designed to the same rulebook: Eurocode 5. If you are an architect, contractor, or self-builder working with timber, it helps to understand what this code is, what it controls, and why it shapes the screws, connectors, and details that end up on your project. This guide explains Eurocode 5 in plain terms, without the equations.
What Eurocode 5 is
Eurocode 5, formally EN 1995, is the European standard for the structural design of timber. It is one of a family of Eurocodes covering different materials, and it remains the basis for timber design in the UK, used alongside the UK National Annex, which sets the country-specific values. Its job is to make sure a timber structure is strong enough, stiff enough, and durable enough for its intended life, under every load it will reasonably see.
The main part, EN 1995-1-1, covers general rules and the design of members and connections. Further parts deal with fire design and with bridges. For most building work, the first part is where the design lives.
The two things every design must satisfy
Eurocode 5 checks a structure against two limit states, and both must pass.
| Limit state | The question it answers | Examples |
|---|---|---|
| Ultimate (ULS) | Is it strong enough not to fail or collapse? | Bending, shear, connection capacity, buckling |
| Serviceability (SLS) | Does it behave acceptably in normal use? | Deflection, vibration, bounce in floors |
A timber floor often passes the strength check easily but is governed by serviceability, because timber is light and can feel bouncy. Designing to Eurocode 5 means satisfying both, not just the one that is easiest to meet.
Why timber is designed differently to steel or concrete
Timber is a natural material, and the code accounts for behaviours the others do not have. Two factors stand out, and they appear throughout Eurocode 5 calculations.
- Load duration. Timber carries a short-term load, such as a wind gust, far better than the same load applied permanently. The code captures this with a modification factor, so the same member has different capacities for different load types.
- Moisture, or service class. Timber in a warm dry interior is stronger and stiffer than the same timber outdoors or in damp conditions. Eurocode 5 sorts environments into service classes that adjust the design values accordingly.
In practice: these two factors combine into a single modification, kmod, that scales the timber's strength to suit how long the load lasts and how wet the environment is. It is why a timber design cannot simply copy a steel approach.
Connections: where Eurocode 5 does the most work
Timber members are usually generous; the connections are where projects are won or lost. Section 8 of Eurocode 5 governs connections made with dowel-type fasteners, the screws, dowels, bolts, and nails that hold timber together. Capacities come from the European Yield Model, which predicts how a fastened joint fails based on the geometry and the timber's resistance to the fastener crushing into it. Spacing, edge distances, and the number of fasteners in a row all feed directly into the result.
This is why connection design, not member sizing, is usually the critical path on a timber project, and why the connector and screw schedule carries so much of the engineering and the cost. It is the subject of our companion guide on CLT connection design to Eurocode 5.
Where assessed products fit in
Eurocode 5 gives the design framework, but the specific capacities of modern structural screws and connectors come from European Technical Assessments. An ETA turns a manufactured product into design values an engineer can use directly: withdrawal strength for a screw, tensile capacity for a hold-down, shear capacity for a bracket. Designing with assessed products, fixed exactly as the assessment requires, is what makes a Eurocode 5 calculation reflect what is actually built.
What this means for your project
You do not need to run the equations yourself, but understanding Eurocode 5 explains why a timber engineer asks the questions they do: how long does each load last, how wet is the environment, how does load pass through the connections, and which assessed products achieve it. Getting those answers right at design stage is what produces a structure that is safe, compliant, and economical, rather than over-built or under-designed.
Eurocode 5 design with TimbA
TimbA Systems pairs UK structural timber engineering with the connection hardware to build it. Our engineering team designs timber members and connections to Eurocode 5, from floor and roof framing to hold-downs and tensile plates and full CLT connection schedules, and supplies the matching structural screws and connectors from stock. If you have a timber project that needs designing or checking, talk to us early, when the code's decisions still shape cost and programme rather than constrain them.
