Code complications

Eurocode 5 (EC5) was hailed as the industry solution to deliver a uniform approach to timber roof truss design, but its false start has left many unsure as to what the delay will mean for them.

Since the introduction of EC5 and all its supporting codes, and the withdrawal of the British and Irish Standards it replaces, companies in the timber engineering world have been working hard to acquaint themselves with the requirements of the new codes.

EC5, unlike its predecessor, is largely formulaic with very few tables of results and much is left to the discretion and interpretation of the engineer.

For providers of structural design software, the burden of interpretation lies with their engineers and programmers and the old adage that “two heads are better than one” has been adopted by the roof truss industry in a pragmatic approach to this issue.

For more than 24 months, those in the nail plate system industry have been meeting on a regular basis to discuss technical issues relating to the interpretation and implementation of the new code. In addition to implementing the information currently available, there are other items which are yet to be finalised and published by the code committees.

We should remember that this code has been introduced not because of technical concerns over the Standards it replaces, but as part and parcel of the European Union’s ethos of free movement of goods and services within the EU, achieved in this Case by provision of common rules for calculation and design.

Consequently we are in a fortunate position whereby designs produced using EC5 can be compared to those using the British or Irish Standards to ensure that the results are broadly the same, as the ‘real-world’ loads these structures have to support haven’t changed.

Some housing associations and local government offices have been quick to specify EC5, as is their prerogative, on certain projects but full acceptance is unlikely to occur in England until the National Building Regulations are updated in 2013.

A further complication exists within the timber frame industry where an alternative method of design has been proposed by industry to that which appears in the code. This has yet to be agreed and finalised so situations could arise where one component is designed to EC5 and the other to a British Standard which, although not an insurmountable problem, is far from ideal.

We can slowly start to move forward to bring a design code into place that benefits everyone, but until the issues surrounding Eurocode 5 are completely finalised, designers should be particularly cautious so as to avoid any compliance problems and, above all, ensure that an appropriate structural solution is produced.