When housebuilder Barratt Homes banned the use of steel beams supporting trusses and infill rafters for constructing the roof for room-in-the-roof properties, Pasquill stepped in with a timber-based solution – Safe Span.
“The main problem identified with the original method was that masonry walls, which were built up to support steel beams, were unstable during construction,” explained Pasquill managing director Stuart McKill. “Previous systems, which used steel purlins fixed on to internal walls, had been shown to detach from uncured masonry during high winds, so a safer alternative was required.”
Timber’s environmental credentials compared with steel was another reason that Barratt considered a new solution.
Pasquill looked at replacing the masonry with timber-framed walls and also took the opportunity to swap the steel purlins for glulam. The result is Safe Span, a timber roof truss construction which incorporates spandrel wall panels and glulam beams with top hat trusses.
Prefabricated and insulated gable wall spandrel panels and party wall spandrel panels are initially fixed in place with temporary support bracing frames. At ground level, trussed rafters are fixed to two glulam beams and then lifted into position, set into pockets designed within the spandrel panels and secured using framing anchors. Both trusses adjacent to the party walls are then fixed to the spandrel panels using Z clips, before infill rafters are installed and secured at either end.
Once the main structure is in place, dormer and roof light openings can be cut, and additional timbers installed as required. Gable ladders are then introduced, with sheathing ply and wire-reinforced mineral wood added before joists are installed and secured.
Successful trials
Following trials of Safe Span on three Barratt sites, the housebuilder recommended that the glulam beams be supplied cut to length; the width of the socket in the base spandrel be increased to give greater build tolerance; and the width of the gable ladders be reduced to increase manoeuvrability.
The system is now being rolled out on other Barratt developments.
“The strength and rigidity of glulam provides a viable alternative to steel, providing a cost-effective system which can be installed without the need to employ specialist contractors, enabling housebuilders to use their own tradesmen and save on external labour costs,” said Mr McKill.
The system also reduces the amount of internal scaffolding required and the health and safety issues associated with erecting blockwork and steel beam systems.
Mr McKill said he was very pleased that Barratt had decided to adopt Safe Span on a wider scale.
“It’s not a fully encompassing solution for all situations but certainly where Barratt has traditionally used steel for the top hats, they’ve adopted this solution and they’re encouraging their regions to work with it,” he said.
Pasquill hopes that other housebuilders will turn to the system too, especially because improvements in health and safety mean spandrel panels are being used more widely.
“The use of spandrel panels is increasing for this type of solution and there’s no doubt that a system like this, which effectively hangs off the spandrel panels, will be adopted by other housebuilders,” said Mr Pasquill.
