Composite door bowing tolerances remain the subject of heated industry debate with callbacks costing contractors thousands each year.
“All building products have tolerances. That’s accepted,” says Ian Longbottom, Managing Director, Builders Choice Ltd. “In composite door manufacture, however, slab bowing tolerances seem to be being set completely arbitrarily. We’re being told by builders that some manufacturers argue that 8mm tolerances are simply ‘par for the course’”.
“We’re not, however, dealing in what’s acceptable according to a technical manual. It’s about the reality on the ground and ultimately what’s acceptable to the end-user”.
“If a door won’t open or close properly if the weather sealing fails or the locking mechanism sticks because the slab has bowed, builders and installers are going to get callbacks, and that costs, with the contractor, not the manufacturer picking up the bill.”
Out of tolerance doors are a clear problem at the point of installation. Bowing carries significant potential to impact on the performance of locking mechanisms and seals. This, according to Ian has become a more significant issue as slabs have been redesigned to include more timber to address security concerns. “The trigger was the latest standard PAS24:2016 (now enshrined in Approved Document Q) and particularly cut-through testing, which exposed a fundamental and underlying vulnerability in the make-up of composites”, says Ian. “This drove fabricators and installers toward slab manufacturers who use solid timber in their designs, addressing issues around cut through tests but creating others in the process”.