Wind Uplift Performance of Composite Metal Roof Assemblies

Abstract

A common factor in roof failures is wind forces, which inflict considerable damage every year, even to new roof structures. Metal roofs are a popular low-sloped roof assembly. On the basis of their layout, metal roofs can be categorized as either composite or noncomposite assemblies. In North American practice, five main test procedures—ASTM E1592, ANSI/FM 4474, UL 580, UL 1817, and CSA A123.21-04—are used to determine the wind uplift performance of metal roofs. The fundamental differences between these test protocols lie in the way they represent wind effects on the performance of metal roofing systems. Of the five, CSA A 123.21-04 is the only one that assesses the wind uplift resistance under dynamic wind load conditions. To evaluate the wind uplift performance of noncomposite and composite metal roofing assemblies, eight assemblies with two different types of panels—SNAP-IT and MR-24—were tested by using the CSA A123.21-04 dynamic test protocol. By relating air intrusion characteristics of the subsurface components to panel behavior, this paper shows how composite assemblies resist wind uplift pressures better than noncomposite assemblies. This paper reveals that increased air intrusion resistance of the sub surface components in composite assemblies results in increased suction resistance, decreased panel deflection, decreased stress on the panels, and increased wind uplift resistance.