Slate roofing is known for its durability and classic look.
Photo courtesy of American Slate Co.

By Jennie Farnsworth

Slate roofing is a wonderful way to top off any residential, commercial or public construction project. Slate roofing is known for its tremendous durability — lasting 100, 200, even 400 years — and offers incredible thermal stability, low water absorption, and resistance to acids and chemicals. The system also has unique capabilities to allow for removal and interchanging of parts for ease of maintenance and repair, making this long-lasting natural stone the ultimate roofing material.

History
The formation of slate within the Earth's crust started more than 500 million years ago. A fine-grained, metamorphic rock, slate is formed through a sedimentary process, stacking clay, volcanic ash and other elements to create a shale-type, foliated stone. Slate typically offers two lines of breakability — a cleavage and a grain line — making it easily possible to split the stone into thin, durable sheets for use as roofing material, building veneer, interior and exterior tile, and — for slate not containing feldspar — aquatic décor.

In the United States, slate roofing first came into limited use during the late-17th century, with the material only being used on the stateliest of town buildings. Prior to the age of major transportation, slate roofing was restricted to coastal cities, utilizing materials imported from Wales. However, from 1785 to 1870, the Welsh discovered and opened slate quarries from Maryland to Maine, providing a new local supply. Later, the growing use of locomotive transportation services created an opportunity to supply slate for roofing and other building needs across the United States, beyond the coastal areas and regions local to the quarries.

Slate roofing is available in a number of styles, with the traditional look being the standard pattern shown here.
Photo courtesy of American Slate Co.

From the 1850s to the 1920s, slate roofing was at its height of use in the United States. This period of time introduced the transition of roofing from a typically conservative and low-key structure to a more decorative and high-profile appearance. For many design styles of the time — from Victorian, Victorian High Gothic and Richardson Romanesque, to Georgian, Tudor and Jacobethan Revival — slate became the perfect roofing material to compliment the architects' creations.

After decades of remaining in the shadows with the design community, slate roofing once again made a resurgence, beginning in the 1990s. With the tremendous expansion in the residential construction market in recent years, economic growth in the United States, an increase in historical renovations, and the opening of more slate quarries, slate roofing is making a comeback.

Domestically, slate is now quarried in a number of states, including Vermont, New York, Pennsylvania and Virginia; slate also has been quarried in Arkansas, California, Georgia, Maine, Maryland, New Jersey, Utah and Wisconsin as well, having since ceased production. Internationally, slate is found on practically every continent, with virtually every country that offers natural stone quarrying operations represented. The Glendyne Quarry of St. Mark du Lac Long, Quebec, Canada, is the largest roofing-slate producing facility in North America and one of the largest in the world.

Although the eyebrow dormers and arches provided a challenge for the slate roofers, the Tinley Park station project went off without a hitch.
Photo courtesy of Legat Architects

Colorful Options & Designs
Of all the roofing materials possible, slate is perhaps the most aesthetically pleasing. No other material combines the quality and durability of slate, with the multitude of bursting colors, patterns and designs.

The colors traditionally utilized for roofing include every shade of dark black to milky grey, sea green, robust purples and even a bright red slate. The roofing tiles are available in solid colors or a transitional blend of two or three swirling colors on each tile. As the color of slate is determined by its chemical and mineralogical composition, factors that differ upon the location, each quarry will provide a very specialized variety of colors, tones and shades. The color quality and characteristics are also dependent on other elements present; for instance, the black slate quarried in Buckingham County, Va., offers a distinct, glistening sheen because of its high mica content.

Natural slate roofing tiles typically are characterized as having faded or unfaded coloring. While slate's color does not technically "fade," faded slate roofing will present a chalk-ashen residue over time that may lessen its appearance, while unfaded slate tiles will not. It is also typical that many slate tiles will display varying degrees of color change or weathering because of oxidation of the minerals present in the stone as they become exposed to the elements.

Not only can designers have great artistic license through the use of various colors and color combinations, but slate roofing also offers a broad range of creative inscriptions or designs, as well as traditional patterns, including standard pattern, random width, staggered butt, ragged butt, textural, graduated and mixed shapes styles.

Although the eyebrow dormers and arches provided a challenge for the slate roofers, the Tinley Park station project went off without a hitch.
Photo courtesy of Legat Architects

Life Cycle & Durability
What makes a slate roof expensive is its initial cost; however, over years it provides a pleasant appearance while needing little maintenance. The life cycle for a properly installed slate roof is usually more than 100 years, with the longevity typically dependent on the type and origin of the slate, the roof style and climate in which the building is located.

To support long life, slate roofs should be inspected annually and after severe storms. Even if a tile is damaged, maintenance and repairs of slate roofing systems are accommodated easily.

Case Study
Recently chosen at the American Institute of Architects' list of 150 Great Places in Illinois, the Tinley Park Oak Park Avenue Metra station designed by Legat Architects of Waukegan, Ill., provides Old World charm and sensibility that offered the perfect opportunity to utilize slate roofing.

Completed in 2002, the train station was the first step in this thriving southwest Chicago community's master plan aimed at renovating the town's image. The station is the pivotal element in creating a warm and socially active central area for the town, sporting Fond du Lac Rustic stone walls from Buechel Stone, exposed wood rafters, and cedar shingle siding that recalls the "Arts & Crafts" style popularized at the turn of the century.

Taking this stylish design further, if one were to look down upon the building from above, the station's three-story clock tower and observation deck serves as the center point of a "clock face," with the "hour hand" housing the waiting area and the "minute hand" housing the Internet café and covered passenger drop-off area. Stone monuments around the plaza mark each hour on the clock's face.

With so much forethought and creativity in the design, it was hard not to choose the perfect roofing material for the job.

Designers from Legat Architects of Waukegan, Ill., decided on a grey, green and purple combination of slate tiles for the Tinley Park station project.
Photo courtesy of Legat Architects

"Slate was easily sold on this project," said Marc Rohde, architectural project manager for Legat Architects. "They wanted this project to be top-notch quality, so we were doing real slate, real heavy timber, real stone.

"Architecturally, we were probably first thinking about the look, but at the same time we had to look at the fact that we wanted this building to last at least 50 years," Rohde added. "We really wanted that stone and Old World look, so we went with what we wanted.

"Yes, slate roofing costs more, but it's pretty permanent and it should be a half century, at least, sitting up there," he said. "You're not going to be carrying it off after 20 years."

While slate roofing was relatively a "no brainer" on this project, Rohde and his team spent time looking over color samples, mixing combinations together and deciding on the final look that epitomized the Tinley Park project. In the end, a grey, green and purple slate combination provided exactly what they were looking for.

At the installation stage, although the eyebrow dormers, arches and the circular roof of the clock tower provided a challenge for the slate roofers, the project went off without a hitch.

"We're very pleased with how the project turned out," Rohde said.

Resources:
Jenkins, Joseph. Styles of Slate Roof Installations. Retrieved May 16, 2007, from the Slate Roof Central website: http://www.jenkinsslate.com/install_styles.htm

Levine, Jeffrey S. (1997). Slate Roofs in America: A short history by Jeffrey S. Levine. Retrieved May 15, 2007, from the Partners for Sacred Places website: http://www.sacredplaces.org/PSP-InfoClearingHouse/articles/
Slate%20Roofs%20in%20America.htm

Marshall, Philip Cryan and Collins, Allison Brooks (1999). Slated for Preservation, presented at The Roofing Conference and Exposition for Historic Buildings, Philadelphia, Pa., March 17-19, 1999. Retrieved May 15, 2007, from http://www.philipmarshall.net/Publications/NPS_Roofing_Conference_1999.htm

Perazzo, Peggy B. (2007). The Slate Industry. Retrieved May 14, 2007, from the Stone Quarries and Beyond website: http://www.cagenweb.com/quarries/
articles_and_books/us_geo_survey1894_slate.html

Prudehome, Bill (2007). Slate & Tile Roofing — The Facts! Retrieved May 15, 2007, from the Ezine Articles website: http://ezinearticles.com/?Slate-and-Tile-Roofing-The-Facts!&id=499591

Slate, retrieved May 14, 2007, from the Wikipedia website: http://www.wikipedia.org

Smid, Chuck (2004). North American Roofing Slates. Retrieved May 16, 2007, from the National Slate Association website: http://www.slateassociation.org/downloads/slate-descriptions.doc

• Return to table of contents

www.buildingstonemagazine.com

Building Stone Magazine
©2007 by Building Stone Institute
www.buildingstoneinstitute.org
All rights reserved

Web Site by:
Lionheart Publishing, Inc.
506 Roswell Street, Suite 220, Marietta, GA 30060
Phone: 770-431-0867 | Fax: 770-432-6969
lpi@lionhrtpub.com
www.lionhrtpub.com