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An interesting situation has arisen where Building Control are telling builders who have erected structures using TRADA Technology Span Tables to BS 5268 that they must rebuild using the Eurocode 5 version of the tables. This is incorrect and stems from misinterpretation of guidance issued by CLG in January 2010 when they wrote to pave the way for the Eurocodes.
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TRADA Technology has been contacted by builders advised by Building Control that they might need to rebuild roofs and other structures if built using the BS 5268 version of its Span tables for solid timber members in dwellings, instead of the Eurocode 5 (EC5) version, as the result of a misinterpretation of guidance issued by the Department of Communities and Local Government (CLG).
CLG contacted local authorities, Building Control, approved inspectors and other interested bodies on 29th January 2010* about the introduction of the Eurocodes, and the associated withdrawal by British Standards Institution (BSI), in March that year, of conflicting BS design standards. Some of these design standards, including BS 5268, are referenced in the Building Regulations Approved Documents, particularly Approved Document A (Structure).
When assessing compliance with the Building Regulations, Building Control Bodies (BCBs) were advised in the CLG communication to 'continue to consider the appropriate use of relevant standards on a case by case basis. This may include the use of the new BS ENs, which formally become the new national standards in April 2010 reflecting the changes made by the standards organisations.'
The withdrawn British Standards remain available from BSI, but BSI committees had already stopped updating those British Standards well before they were withdrawn, and so, said CLG, 'they may not necessarily be suitable for aspects of structural design in the medium and long term'.
It is this part of the communication from CLG which appears to have caused some confusion. Until 2004, the span tables were included in Approved Document A (ADA). Then TRADA Technology was asked to take over their publication and ADA 2004 references the TRADA Technology document, now in its second edition. Five years later, to prepare for the advent of EC5, TRADA re-calculated the span tables to comply with Eurocodes and published a 3rd edition, in anticipation of a further updated version of ADA, due to be published in 2013. Because BS 5268 is still referenced in Approved Document A, however, the 2nd and 3rd editions of the span tables have been sold concurrently, for calculations to BS 5268 and Eurocode 5 respectively. This was done, said Dr Hugh Mansfield-Williams, TRADA Technology Principal Consultant, 'to ease the transition from one design standard to another, but in the knowledge that designers would be reluctant to change overnight'.
And he stressed, 'Although TRADA naturally wants to encourage a complete move to EC5 technically - and we strongly discourage designers from "mixing and matching" the old and the new standards - it would be incorrect to say that builders cannot build to the withdrawn standards, because the revised version of ADA will not be in place until 2013. We believe this is the correct interpretation of the CLG guidance.'
In its January 2010 communication CLG stated, 'When an Approved Document makes reference to a named standard, the relevant version of the standard is the one listed at the end of the publication. However, if this version has been revised or updated by the issuing standards body, the new version may be used as a source of guidance provided it continues to address the relevant requirements of the Regulations.'
When the communication was issued, CLG was evaluating Parts A (Structure) and C (Site preparation and resistance to contaminants and moisture) and their Approved Documents. It said, 'We are looking at these Parts together as they target similar building elements. The evaluation has identified a number of issues that Parts A and C will need to reflect, but the full implications of these issues will not become clear until later this year at the earliest, ie too late to inform changes in 2010. We have concluded, therefore, that we should continue our work reviewing Parts A and C, with a view to proposing appropriate changes for the next periodic amendment in 2013. We expect to be updating at that time the references in the Approved Documents that relate to structural design standards.'
Importantly, the communication affirmed: 'However, we would not expect this rescheduling to affect or deter the take up of the new national standards (BS ENs), based on Eurocodes. We continue to work with industry including professional institutions and representative bodies, to assist as they prepare for this change to the British Standards.'
Contact Information
Jean Kloos
BM TRADA Group
Stocking Lane
Hughenden Valley
High Wycombe
Bucks
HP14 4ND
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