"Synthetic" as it pertains to steep-slope roofing materials refers to manufactured products that replicate asphalt shingles, concrete tile, clay tile, metal panels, slate, wood shakes and wood shingles. Synthetic roof coverings contain recycled plastic and/or rubber as a key ingredient. These products have been available since 1993.
There are some advantages to using synthetic roof coverings when compared to their traditional counterparts. Synthetic slate, or "fake slate," for example, weighs substantially less than natural slate. The reduction in weight allows synthetic slate to be installed over conventional roof decks. Some synthetic products purport to be hail-, mold- and algae-resistant. Several synthetic cedar shake and cedar shingle manufacturers claim a labor savings, because fire-retardants or anti-algae coatings do not have to be applied to the product.
Despite the benefits, there are some significant drawbacks. Synthetic roof coverings are relatively new and there isn't a proven track record about their performance. Most synthetic products are manufactured with dyes or coloring agents and it is unknown whether these products will fade because of ultra-violet exposure and weathering. It also is unknown whether these products will become more brittle or less flexible over time. And most important, model building codes do not recognize any synthetic roof coverings. You need to check with your local building department before installing these products. Because of these reasons, caution should be exercised when using synthetic roof covering products.
Currently, there are no ASTM International standards for synthetic steep-slope roof covering products.