During the last decade, hundreds of composite roofing materials that mimic natural slate have been introduced to the market. Most of these have been fiber-reinforced cement, fiber-reinforced recycled plastics, or recycled rubber molded to look like slate, wood shakes, or clay tile. But although the materials in different products sometimes share similarities, they may vary widely in performance.

It's important not to lump all composite products together, cautions Mark Graham, associate executive director of technical services for the National Roof Contractors Association. He urges contractors to evaluate each product separately, and to be diligent about tracking reports of problems.

Trouble for the composite roofing industry began in the late 1990s when early fiber-cement entries began delaminating and crumbling. As a result of several class action lawsuits, all of which were settled in recent years, manufacturers have either discontinued or re-engineered their fiber-cement roofing product lines.

But not all have fled the synthetic slate market. Carlisle (maker of Majestic Tile), DaVinci Roofscapes, TAMKO (maker of Lamarite Slate), and Slate/Select claim growing sales of their product lines and are quick to point out the differences in their products that make them less susceptible to problems. Majestic Tile is made from 100% recycled rubber. TAMKO and DaVinci use a polymer and limestone mixture. Slate/Select uses glass fibers instead of cellulose. All can be air-nailed into place, and tend to be lighter than natural slate, making them easier to install. Still, they are only minimally cheaper than S1-grade natural slates appropriate for roof applications.

Prices for natural slate vary widely. In some markets the price difference between synthetics and natural slates may be 10% to 15% or more per square; in other markets it may be only a few dollars, up or down. Combined with the fact that composites are generally lighter in weight and easier to cut and fasten however, the savings on synthetic materials can be substantial. Thomson Remodeling in Baltimore, Md., saved $10,000 on a recent job using Lamarite Slate.

Thomson Remodeling runs a division that specializes in slate roofing, and doesn't always opt for synthetics, however. “On most of our jobs, we recommend natural slate,” partner David Robinson says. “Good slates will last 100 years. The new materials are still unproven.” Still, Robinson concedes, in some applications — a shallow-pitch porch roof that will see a lot of traffic from painters and gutter-cleaning homeowners, for example — more flexible, polymer-based tiles often make sense.