The Art of Deflection
Of the many issues the C-18 committee discussed regarding thin wall adhered veneer and proposed specifications, expansion joint spacing, stone weight, system weight, maximum height, inspections, etc., nothing inspires heated debate like the issue of allowable deflection of the back up structure. The contention began with a proposed requirement of a maximum allowable deflection of L/1000. L is the span, or the free length of the back up structure between supports. So, if the distance from the floor to the structure above is 10’, then that is the span. L/1000 then, is 120” (10’) divided by 1000 or 0.120”, about 1/8”. What this means is that a 10’ wall should only move 1/8” at the center of the span when the full design wind load is applied.