Nonstructural Components and Systems
The single most critical line of defense against property damage from high winds and rain is roof coverings, yet roofing damage is the major driver of recent economic losses in hurricanes and extreme wind events on single - family residential structures. For example, in Hurricane Matthew in 2016, 68 of 265 (26%) single-family residences surveyed by University of Florida Wind Hazard Damage Assessment Team (WHDAG) in Flagler County, Florida, had roof damage. In 2017, Hurricane Irma damaged 140 out of 244 (57%) structure’s roof surveyed by WHDAG, in Everglades City and Marco Island.
Discontinuous metal roofing (DMR) systems have been gaining some market share in residential structures. Tests have shown that metal roof perform well in extreme winds. Discontinuous roofing systems allow air flow through joints in the panels which studies show reduces the wind loading on the panels themselves. As part of a new standard test method being developed at the University of Florida sponsored by MCA (Metal Construction Association), a methodology was developed to determine whether or not a DMR system is sufficiently air permeable to result in reduced wind loading. Currently, no standard test protocol exists to determine the air permeability of a discontinuous metal roofing systems.
The researchers built a text chamber to which the DMR panels are mounted, and air is drawn through the head lap and side laps of the panels. The air flow rate is measured for incremental pressures ranging from 25 Pa to 3 kPa. Once the air flow rate exceeds an established minimum value (determined previously), the system is deemed air permeable and would benefit from a reduced wind failure pressure per ASCE 7-16.