Historic Slate Roofs

Slate is a durable, natural stone material that is a favorite building material and often used for roofing. It is a fine-grained, foliated rock composed primarily from quartz, clay, and mica. Natural slate is known for its beauty, long-lasting durability, and resistance to fading, weathering, and rot. 

Slate forms naturally inside the Earth due to a process called metamorphism: rocks are subjected to ultra high pressure, temperature, or both. When shale, a sedimentary rock, is subjected to these conditions it can metamorphose into slate. The clay (etc) minerals rearrange and compact, foliating over time. This parallel arrangement is why slate can be cleaved into thin sheets, making it a naturally capable building material.

Because slate is naturally derived and long-lasting, it's a more sustainable option than synthetic roofing products; slate can be easily recycled and reused, whether for roofing or other applications. In fact, The Durable Slate Company has one of America's largest stocks of reclaimed slate and we often use this material to match existing slates or to reroof a new building, but for a more weathered look.

Slate has been used in roofing applications for centuries, with the first recorded use going back to ancient Rome. Here, they used slate for roofing and other decorative purposes. Medival Europe also put slate to good use throughout its ambitious churches and castles. Later, during the Industrial Revolution, the production of slate tiles became more efficient, reducing cost, making the material more available generally.

To date, there are numerous historic buildings, dating to 15th century or earlier, with historic slate roofs. For example, the Old House in Cirencester, England, is a timber-framed building built in the 14th century. It features a slate roof. The Old Town Hall in Czech Republic dates back o the 15th century and also has a slate roof. Other examples date all the way back to the 12th century. Incredible.

In the United States, slate has been a popular choice since the 17th century. By the 19th century, slate roofed most of our finest buildings, including grand mansions, churches, and government buildings. Many of which have survived to this day, with a bit of maintenance. Slate remains a popular choice world-wide and is often used for new buildings with an eye to the distant future.

Natural, earth-born slate is materially different from so-called synthetic slate options.

Natural slate is an extremely durable roofing material that can last for over a century with proper installation and maintenance. It’s resistant to fire, insects, and mildew, making it a great choice for both residential and commercial buildings.

The process for making roofing slate is labor intensive, but quite straight forward. First, explore and locate suitable deposits of slate rock. Geologists use various techniques to identify areas where slate is likely to be found, such as analyzing rock formations and studying aerial or satellite images. Once a suitable deposit of slate has been located, it is quarried using heavy machinery such as excavators and drills. Once excavated, the raw material is transferred to a processing plant for cutting, splitting and shaping. Roofing slate gets split into "books" using specialized tools, like fissuring hammers. The books are split into half, quarters, eights, on down until desired thickness. Then, the slate gets cut to size. Finally, it is sorted by size, thickness, and quality.

From beginning to end, roofing slate fabrication is a very labor-intensive process. But the result is hard to argue. The unique qualities of each slate piece, taken together, produce a roof unlike any other. Durable, lasting, and forever one-of-a-kind.

In contrast, artificial slate is not slate at all, rather just a play on words. It's made by molding a combination of materials, such as rubber or plastic, into something that kind-of resembles natural slate. Manufacturing synthetic slate involves a few steps: First, the raw materials are mixed together and poured into molds that simulate real slate. Although factories are best at making identical products quickly, natural slates are each unique. Artificial molds, then, add a bit of variation to the line to make the product look a bit more authentic. Once the rubber-plastic mixture has cooled and hardened, the piece is removed from the mold and inspected for defects. The survivors are cut to size and packaged up for shipping.

Synthetic slate can be made from various materials, such as PVC, TPO, EPDM and other thermoplastics. Some types of synthetic slate are created with a precise ratio of recycled materials, making them a tad more eco-friendly than unrecycled products. Overall, the better fake slates are made from higher quality materials and more time is taken to make them resemble actual slate. Artificial slate has the advantage of being lighter (so easier to ship and install) and less expensive to purchase and install. This makes sense; it’s plastic, not stone. And because it isn’t real stone, the trade-offs are plain:

Crucially, synthetic slate is not as durable as natural slate. Real slate has centuries of evidence to prove beyond any doubt that it is robust material for roofing. Fake slate is a relatively new product and simply hasn’t established itself as a no-compromise alternative. Despite the manufacturer’s claim, fake slate is more likely to show serious wear much, much sooner than the real thing. This includes discoloration and various deformities, like curling and cracking. And although they make the effort, there’s no practical way to make every synthetic slate tile as unique as real slate. On a roof, this limited variation blends together into something bland and uniform looking. A bit like asphalt shingles, they lose their character and chunky quality and end up looking manufactured and uninteresting.

Besides this, synthetic slate’s durability problem implies more maintenance over time and a higher total cost. Natural slate is resistant to fire, insects, and mildew and doesn’t require much, if any, special maintenance. A slate may replaced from time to time, but the rock itself wears wonderfully. Plastics, though, are susceptible to ultra-violet light and other environmental factors that cause discoloration, fading, and cracking, ruining the material and compromising the water-tightness of your roof. Damaged tiles are not (and typically cannot) be repurposed or recycled, creating heaps of unnecessary waste. Contrasted against natural slate which may outlast the building it’s on and love being repurposed.

Synthetic slate is materially like other manufactured roofing products, including asphalt shingles. Run-of-the-mill roofers treat synthetic slate as a top-shelf option that resembles slate, but can be installed quickly and imprecisely, like standard roofing shingles. As with real slate, improper installation will shorten fake slate’s intended lifespan. Overtight nails, for example, give the plastic material too little room to move as it heats and cools and contributes to cracks, slippage, and deformation. Fake or not, even these plastic sheets need to be installed correctly to function properly.

Overall, synthetic slate is lighter, but vastly inferior to natural slate. It’s less durable, less beautiful, and more environmentally hazardous. It may be a little cheaper up front, but with elevated, unknown costs and excessive environmental waste.

Brass tacks: real slate is heavier and more expensive up-front than fake slate. The weight increases manufacturing and shipping costs (putting a premium on good logistics) and makes installation more difficult and specialized. Heavy duty materials take time, energy, and expertise to install properly, no matter the century. But once installed, slate roofs are more likely to withstand the worst that nature has to offer, such as hurricanes, heavy snow, and high winds. Expert installation, good quality slate, and observance of local codes are crucial, of course. An amateur roof built with inferior slate can still peel away in heavy winds.

Besides the durability, natural slate is more beautiful than any artificial alternative. The variation in color, shape, and thickness per piece combine into a truly unique roof. Expert slaters will arrange the slates just-so, for the best possible fit and picture, producing a water tight roof that looks wonderful no matter the viewing distance, weather, or century. That durability is an aesthetic factor too; reclaimed or recycled slate is popular among architects who want a worn look or for seamless repairs to older slate roofs. Well treated roofing slates have long, interesting lives. Sometimes on multiple buildings across decades (or longer).

In sum, fake slate is cheaper to buy and install. But the compromise is longevity and appeal. Natural slate is more expensive, initially, but has an indefinite lifespan if installed properly (decades or centuries, depending on the hardness of the slate and quality of the install). Fake slate produces more waste and is useless if damaged or beyond its functional life. Real slate, however, has a different character depending on its origin, age, and environmental exposure, and can often be reused for a different project. Indeed, reclaimed slate is perfect for a weathered, antique look that doesn’t skimp on durability or authenticity.

The Durable Slate Company provides slate roof repair, installation, and restoration services world-wide. We began humbly as a small slate roofing company in Columbus, Ohio, and through a mastery of historic repair methods and a focus on exceptional customer service, we have grown to become one of the largest slate roofing companies in the United States with offices located throughout Ohio and Maryland, including Columbus, Cleveland, Cincinnati, OH, and Savage, MD.

Thanks in no small part to our extensive repair experience and history, The Durable Slate Company is able to handle any slate roof repair or installation of any size on any kind of building.

And with such a large stock of reclaimed slate in America, we can match most original slate for an exceptionally seamless repair or full roof replacement. If your slate roof has been damaged by fire, wind, storm, other forces of nature, or just requires a bit of upkeep, you can be confident in The Durable Slate Company for your slate roof repair needs.

Reclaimed slate can also be great for new installations, allowing a wonderfully aged and classic look, without having to wait a century. Likewise, if an antique roof’s slate shingles are in good condition, it is often possible to install new underlayment and copper flashing, preserving the original slate, and matching damaged tiles from our reclaimed slate stores.

A thorough evaluation by a professional is provided by The Durable Slate Company at no additional cost to you to determine what is best for your slate roof.

For installations with new slate, we prefer to install only the highest quality time-tested slates from the quarries of the Vermont Slate Valley, Virginia Buckingham, Southeastern Canada, Wales, and certain select European quarries. The combination of high quality slate, expert flashing design and installation, correct soldering, necessary underlayments for the conditions, and proper slate laying and fastening produces an aesthetic, long lasting roof that should have a serviceable life of 100 years or longer.

Cutting corners on any one of these factors can shorten the life span of a slate roof from a century to a few years or less. We have replaced numerous slate roofs that were less than 10 years old because an essential craft was neglected.

Though quite beautiful, many imported slates are of such poor quality that they start rusting and falling apart within only a few years of installation.

A high quality slate is as essential as a reliable, expert slater.