The end of last year marked the close of a three-year co-existence period between the British Standards and the new Eurocodes. Subsequently, the Trussed Rafter Association and the independent UK Engineered Wood Products Committee, which oversees the design of I-joist and metal-web beams, have been working to encourage engineers to make the Eurocode transfer as soon as possible.

Eurocodes have not been introduced because our current British legislation is inadequate. Rather, their objective is to provide a pan-European building code that provides common design criteria, understanding of design and helps promote trade across the board. The new codes should also build a solid foundation for research and development, as well as a platform for design aids and software.

The EC5 is made up of three parts and each has a National Annex (called PD6693 in the case of the UK), which contains country-specific design data for local conditions such as wind speed and snowfall. Following the BSI's ratification of PD6693 in 2006, the Eurocode officially became an alternative to BS 5268. It has been possible to work to EC5 since then, and large structural engineering practices are already using the new code due to the benefits of pan-European trade.

However at present it seems unlikely that the industry as a whole is equipped or ready to make the switch. Many manufacturers and engineers still don't realise the importance of employing EC5, and indeed the other respective Eurocodes, as standard working practice. There are several reasons for this, aside from the technical differences. Within the industry there has been no 'official' axing of the BS 5268, instead it has existed alongside the new Eurocodes, leading to the perceived impression that designing, and subsequently building, to this standard is still accepted practice. Furthermore, many end users have failed to prepare correctly for the migration, despite public procurement rules demanding that EC5 be used for all public sector building.

The current situation could lead to floors and trussed rafter roofs being designed to EC5 and timber walls to British Standards. It is important to stress, however, that one approach must be taken. Projects that are specified to EC5 can't use products designed to BS 5268 as combining the two could lead to a mismatch of components and subsequent problems during the build.

It's also worth noting that professional indemnity insurance has a large part to play in ensuring engineers switch to the Eurocodes. If work has been completed to the old British Standard and there are mistakes that need to be rectified, companies may find themselves on the wrong side of a litigation case for negligence.

Working stress to limit state

In designing and using timber construction components, EC5 means engineers switching from the working stress methods applied under British standards to limit state methods. However, because many changed to the latter working with steel, concrete and masonry a number of years ago, this shouldn't have too much of an impact.

In design terms, the fundamental difference between the two standards is that EC5 is a theoretical code where formulae replace tabulated values, rather than a code of best practice. The result is that it lacks the easy reference tables of BS 5268, but this is where the National Annex comes in. It includes tables of loads and other design data that were included in BS 6258 in addition to the country-specific material properties.

Although EC5 takes a less prescriptive approach to design than BS 5268, it will require far more understanding and vigilant application from engineers. In addition, characteristic strength properties for panel products and components such as timber I-joists and metal hardware must now be obtained in accordance with CEN testing standards.

One of the major items still to be decided is the vibration design on floors/attic trusses and compression splice plate design. If the design follows EC5 then it's important that an appropriate vibration check is carried out, as this is usually the governing design case. After the vibration method has been finalised the National Annex to EC5 will need to be updated and reissued along with PD6693. This provides additional rules on many aspects of timber and truss design not included in EC5.

Software makes the switch easier

Clearly the implementation of the new Eurocodes – specifically European Standard EN 1995, or Eurocode 5 (EC5) – will have a marked effect on timber construction design software and the transition from one code to another will inevitably have its complications and take time.

In this regard Gang-Nail's own software is still in development, despite having a solid foundation to start from. But our products are now designed to work within the parameters of EC5 and we offer full training to ensure that timber engineers can use the new design codes to improve timber design. We also check against existing British Standard requirements to make sure there are no fundamental variances between the new and old codes.

We also now have a test version of software covering truss and metal-web floor designs, which features a simple switch to change from either BS or EC5, offering a tool to compare the results rapidly.

Anyone using our software does need to understand the fundamental differences between EC5 and BS and this is where our commitment to training is focused. But, as very little will have changed in the software's user interface, it's unlikely that much, if any, will be needed in this area.

The use of EC5 as the only design method will take some time to filter through the industry, and there are still some unknowns regarding its formulation and implemetation, so software will continue to evolve and expand to meet market requirements over coming years. In this respect Gang-Nail offers users the advantage of an annual update of all software to keep abreast of changes.