Synthetic slate: Fabulous fakes

Owners of older homes are often determined to keep original exterior features such as slate roofs. That is, until the see the price of replacing oneof these roofs. Composition shingles are less expensive, but don't give the samehistoric look and architectural detail.

A new generation of slate look-alikes offer the best of both worlds -- thelook and durability of slate at a lower cost with less weight.

The National Park Service's Historic Preservation briefs recommend repairingor replacing historic architectural material whenever possible. However, thisbible of historic preservation, acknowledges that substitute materials thatreplicate the look of historic materials are being used more and more inpreservation projects, and notes that in many cases the results are positive.

"(Substitute materials) can be cost-effective, can permit the accuratevisual duplication of historic materials, and last a reasonable time. Growingevidence indicates that with proper planning, careful specifications andsupervision, substitute materials can be used successfully in the process ofrestoring the visual appearance of historic resources," according to PreservationBrief # 16, The Use of Substitute Materials on Historic Building Exteriors.

CertainTeed, better known for its composition roofs, offers CeladonCeramic Slate, a tile that combines the thickness, texture and color ofnatural slate with the fired-in strength and durability of ceramic tile. At 580pounds per square, Celadon is among the heaviest of the substitute slate roofingmaterials, but its weight is still only about half that of natural slate.

EcoStar's MajesticSlate and EuroSlateare made from recycled post-industrial waste rubber and plastic, and weighas little as 166 pounds per square, depending on application. The roofingmaterial is derived from EcoStar's "starloy," a product that wasdeveloped for sea dock walkways 20 years ago. Majestic Slate is made from 100percent recycled material and is intended exclusively for historic restoration,while EuroSlate is 60 percent recycled material, and is available in a standardrectangle shape as well as a scalloped edge.

tiles from US Century, are made of recycled steel reinforced rubber fastenedheat welded pockets over the tiles to 2.5 mil high-density polyethylene panels.Every shake is hand-crafted and coated with natural ground slate to createsubtle variations in color and texture. The inherent properties of slatemake it naturally UV resistant, and inhibit the formation of unsightly saltdeposits (efflorescence). The panels weigh 350 pounds per square.

MiraVista,from Owens Corning, looks like the real thing, but is made from from slate andclay reinforced with fiberglass and then bonded with resin. Weighing in at 450pounds per square, MiraVista, like the other imitation slates costs much lessthan natural stone.

The Extension Service of Cornell University estimated roofing costs in 1997,with natural slate costs ranging from $320 to $1,200 per 100 square feet.A natural slate roof will last anywhere from 50 to 100 or more years, and canweigh as little as 600 or as much as 1,200 pounds pounds per square. Afiberglass shingle roof weighs 200 to 425 pounds per square, depending on thequality of shingle, and lasts 15 to 20 years. According to national mortgagebroker Freddie Mac costs $130 to $175 per 100 square feet.

The new generation of synthetic slates fall somewhere between slate andfiberglass shingles in cost and weight. Imitation slate roofs can weigh aslittle as under 200 pounds per square to as much as 600 pounds per square.Manufacturers of synthetic slates estimate the materials life span at 40 to 60years or more.

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