Why Is Slate Used for Roofs?

Updated March 23, 2017

Slate is a natural occurring stone that was formed millions of years ago. It was first mined in the United States for roofing applications in 1785 by William Docher in Pennsylvania. Slate is one of the most durable and longest-lasting roofing materials available.


A slate roof is oftentimes a patchwork of colourful shingles that creates a handcrafted and unique appearance. Available in a variety of colours, the most common colours of slate are grey, blue-grey, black, dark purple, brick red, a variety of green shades and mottled. Slate is also classified as either fading or non-fading. Fading slates react with the atmosphere to fade in colour or streak after a very short exposure time. Non-fading slate will retain its natural colour for many years.


Slate is a metamorphic rock that was formed underground under conditions of high heat and pressure. Slate pieces vary in colour, texture and strength depending on their source minerals and clay content.


When properly installed and maintained, slate roofs can last between 60 and 125 years. Some slate roofs have lasted well over 200 years. The longevity of a slate roof depends on the geological location of the original slate deposit, the type of slate used and the design of the roof.


In 2010, a typical asphalt shingle roof cost between £32 and £97 per square. A slate roof can cost up to £650 per square, depending on the variety of slate. While the cost of a slate roof is considerably higher than other roofing options, it does not require costly maintenance or replacement. Slate also helps to lower a home's energy costs and increase resale value.


Slate roofing weighs about three times more than a traditional asphalt roof. A square of slate can weigh between 318 and 363 Kilogram, whereas typical asphalt shingles weigh between 113 and 181 Kilogram per square. In order to support the weight of a slate roof, framing for the structure must be significantly more reinforced than for other roofing alternatives.


Slate is a maintenance-free roofing material. It is not affected by insects, rot, mould, mildew or algae, and is completely fireproof. Because it is easily broken, slate should not be walked upon and broken tiles should be promptly replaced by a professional.

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