Fiber-Cement Roofing Slates and Shingles

October 30, 2006
Publication: Politecnico di Milano - Italy, Department of Building and Environmental Sciences
Author(s): Cash, Carl G. Stephen Condren Werner Gumpertz

Abstract: Early in the 1980's, manufacturers started to respond to the market desires for a Class A fire-rated steep sloped roofing intensified by fire storms in California where the conventional cedar wood shake roofs were often blamed for the high fire losses experienced.  Other manufacturers sought slate-like roofs that were lower in cost than natural slate.  Both groups tried a variety of materials and cellulose fibers including fibers recovered from newsprint, bundles of wood, and more fibrous or shredded wood to reinforce Portland cement matrixes. Previously, asbestos fiber was used with cement to form very durable asbestos-cement shingles, sidings, and sheets.  The use of asbestos was discontinued in the United States for reasons that are outside the scope of this report, but many manufacturers felt they could replace asbestos with other materials and did so with performance warrantees of from 25 to 50 years duration. The authors have investigated and tested eleven of these fake shakes and slates manufactured by nine manufacturers.  Hundreds of roofs have been examined in over 20 states.  Some failed before the installation was completed. Few survived past their tenth year of exposure. None of these are currently manufactured in the United States. We provide data selected from our laboratory tests on thousands of specimens made by nine manufacturers (A through I), identify the reinforcements present, list some of the critical properties such as flexural strength, deflection at break, and water absorption, and the specific failure modes for each product. The principal recommendation to avoid failures of this kind is to use products that have a substantial history of effective performance in the environment to which they will be used.