New roofs to withstand harsh weather.

Tornadoes, hurricanes, and extreme temperatures are among the harsh conditions that roofs must withstand. Manufacturers who design new roofing materials want to predict how well they will weather such conditions without testing them for years on top of a building.

Scientists at the National Research Council (NRC) in Ottawa, Canada, have come up with new ways to gauge the impact of tough simulated weathering and tornado-like conditions on roofs. Chemist Ralph M. Paroli and his colleagues subject asphalt or polymer-based roofing materials to these conditions in a laboratory environment and monitor changes in chemical and physical properties that indicate the extent of degradation that could be expected during real use. Recommendations from such testing will help consumers and builders select appropriate materials and aid building owners and managers who need to budget for possible repair or replacement of their roofs.

Two of the most common new materials are polyvinyl chloride (PVC) and ethylene-propylene-diene monomer (EPDM) roofing membranes. These single or multi-ply sheets of plastic-like material or asphalt utilized to waterproof or insulate rooftops often are visible on flat-topped buildings.

Paroli and his colleagues have been studying the impact of intense weather conditions on such materials - in particular, the cause of premature shattering of unreinforced PVC and the shrinking of EPDM - using thermogravimetry and dynamic...