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Technical Roofing and Construction Services (trcs for short) prides itself on a record of zero-defects: in almost eight years since it set up in business in Cheltenham, it has never once been called back to a job to undertake remedial work.

Directors Paul Boulton and Len Cooper both worked for Hoogovens before the company moved to Haydock. They decided to stay in Cheltenham and set up their own contracting, fabrication and welding service, both in-house and on-site. They have a portable 3m folder in the back of their Mercedes van and a portable slitter capable of widths of up to 1.25m, so they are familiar with using kal-zipregistered.

They avoid the 'wrinkly tin' market but cope well with smaller and complex jobs, frequently working with architects to try to find ways of achieving challengingdesigns.

Having spent seven years as a design engineer at pmf before joining Hoogovens, Boulton has a strong technical interest in all new roofing systems coming on to the market, and is particularly concerned about 'copycat' kal-zipregistered systems: he suspects that their designers have failed to calculate the tensile and co-existing shear force exerted upon fasteners during thermal expansion and contraction.

'How can a typical modern spacer system, fixed at 600mm centres and held by just two fasteners, produce the same resistance to shear and tensile forces as the patented Hoogovens ST clip fixed to the structural purlin by two stainless steel self-tappers, 6.3mm thick, at 350mm centres? It makes quite a difference.'

There are further concerns about some products and systems which have been found not to meet a building's fire requirements - failing to provide the stipulated 240 minutes of fire resistance.

Unfortunately, once a system has been specified and installed, a subsequently detected compliance failure becomes the responsibility of the architect, not the manufacturer of the system. Convenient.

While no known instances can be quoted to support these concerns, it is worrying nonetheless. Should some manufacturers be taking a close look at the technical specifications of their products and the performance not just of component parts but also of assembled systems?

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