The mandatory requirements for QA of timber products including trussed rafters, like many other commodities we buy from fridges to furniture, are now progressively coming under the harmonisation standards of the European Community. As has been seen in Chapter 1, the standards for design are in a state of flux, and this is also true for those standards relating to quality assurance. CE (from the French Conformité Européan) is the ultimate goal, but whilst most European countries have adopted this, the UK, Ireland, Portugal and Sweden have not. Compliance with CPD (Construction Products Directive) is however mandatory, and this has been enacted in the
UK with the Consumer Products Regulations 1991 amended in 1994. For products where no CE standard exists, manufacturers can apply for an ETA (European Technical Approval), and one such route to achieve this is to follow an ETA guideline known as an ETAG. The following timber related products are currently covered by ETAGs:
• Timber framed building kits
• Prefabricated stair kits
• Log building kits
• 3 dimensional nailing plates
For more detailed information on this subject, the reader is referred to a TRADA publication entitled CE Marking: Implications for Timber Products published in 2004. Additional information on BM TRADA Certification can be found on the TRADA website, details of which can be found in the bibliography.
Currently the trussed rafter industry is still covered by the requirements of BS 5268: Parts 2 and 3 with manufacture quality assurance being in accordance with ISO 9001. The independent certification for ISO 9001 is generally within the industry provided by BM TRADA certification under their Q-Mark scheme. This scheme provides confidence for the specifier, creditability through TRADA's world renowned standing, and traceability. Full details of Q-Mark members and their certified products can be found on the TRADA website. The Q-Mark does not only apply to trussed rafters but many other building materials.
Registered producers are allowed to use the BM TRADA Certification logo on their products and documentation. The Q-Mark indicates a quality assured product within the industry; this additional mark can only be used by firms who are registered to a Q-Mark scheme. Figure 6.3k illustrates an earlier mark prior to the introduction of the Q-Mark, and this and similar marks will be found on trussed rafters produced up to about five years ago. Marks could be applied by ink stamping as was often the case with Fig. 6.3k, but trussed rafters are now only marked by fixing a tear resistant
Timber graded as marked
TRUSSED RAFTER SCHEME
Timber graded as marked
Fig. 6.3k Typical mark prior to Q-Mark scheme.
Trussed Rafters BS 5268:3 BS EN 14250
Fig. 6.3l Q-Mark incorporating bs en 14250.
plastic label under the peak plate on each trussed rafter (Fig. 6.3j); this entrapment under the metal plate ensures that it is not easily detached.
The BM TRADA scheme sets down standards incorporating those in BS 5268: Part 3 and ISO 9001. It also now incorporates BS EN 14250 and a new identification label is now beginning to appear on the product. Whilst there are some modifications to the requirements compared to those printed on the preceding pages, the only ones concerning the end user are found in clause 5 under the heading 'Product Requirements'. Sub-clause 5.1, for instance, specifies strength and stiffness, 5.2 states that a reaction to fire shall be declared, 5.3 dealing with structural members, states that a depth of external members must not be less than 68 mm, and that dimensional accuracy shall be as follows:
Sub-clause 5.4 on joints, the fastener position, states that misplacement must be not greater than 10 mm.
NB: This limit has to be taken account of in the structural design and may vary from system design and requirement with consequent impact on plate size. Again if the reader requires further information reference should be made to the full British Standard.
In summary, as this book goes to press, most trussed rafter manufacturers are using the BM TRADA Q-Mark scheme, and will be marking trusses as illustrated in Fig. 6.3l. This will slowly be moved to a new label which will incorporate BS EN 14250, and ultimately probably through TRADA certification, the product will be CE marked.
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