Most roofs and walls are made of layers. Often, the exterior layer is air-permeable, meaning air can pass through the different layers. When a building experiences pressure from wind, air-permeable coverings allow some pressure to pass through gaps, joints or holes to the layer beneath. This causes a partial equalization, meaning the exterior covering only experiences a portion of the total wind load. This pressure equalization phenomenon is poorly understood and design guidance in current building codes and standards is insufficient and often incorrect. As test standards that try to account for pressure equalization are developed, it is critical that realistic benchmark wind load data is available.
In 2017, IBHS conducted research to provide accurate benchmark data to ensure new standards accurately represent the real wind loads on discontinuous metal roofing (DMR), an air-permeable, panelized steep-slope roofing product made to look like traditional shingles.
The Metal Construction Association selected representative products from the marketplace and provided them to IBHS for testing. Two different types of DMR were installed, each covering one half of the roof area. Results of this testing will help improve existing codes and standards for DMR roof assemblies.