Most users of trussed rafters will first come into contact with the name of one of the plate system manufacturers on receipt of a set of computer printed calculations. If these are not asked for, it is possible that the user may never know which brand of plate has been used in the manufacture of the trussed rafter supplied to him.
The plate manufacturers or 'system owners' supply both plates and design information to trussed rafter manufacturers who, clearly, are free to choose which system they prefer. The choice will be made on plate price, but more importantly (and increasingly a deciding factor) on the degree of design information and technical backup available from the system owner.
Whilst at first sight the type of plate used on the trussed rafter may seem of little importance to the end user, because his contract to purchase trussed rafters is with the trussed rafter manufacturer, it can affect both the quality of service and product supplied - and more importantly the precise construction form used on the roof.
The purchaser should be interested because the system owners, through their various manufacturers, can offer different forms of roof construction, some of which may appear very competitive on first sight but may involve a significantly higher site labour input than an alternative offer. The quality of the fabrication of the trussed rafter is another factor and this, to some extent, will be affected by the machinery and cutting data made available by the system owner to the fabricator. The purchaser is advised to ensure that his supplier is a member of the BM TRADA certification scheme and that the trusses are marked accordingly (see Fig. 6.3j and 6.3k).
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