How Slate Roofing Shingles are Made

Published: Oct. 1, 2018

Slate is a fine-grained, homogeneous rock consisting of volcanic ash and clay. Slate is malleable yet tough enough to be broken into thin sheets or slate shingles. Slate shingles are generally fastened onto roofs with hooks or nails. Slate is available in different sizes that vary from 24” length x 12” width to 12” length x 6” width. Each piece of slate is split by hand.

History of Slate Roofing

Slate roofs first appeared in America in the 16th century but it wasn’t until 1785 until the first slate quarry opened and slate was made available to general consumers. It wasn’t widely used in the United States until the late 1800s.

Slate roofing is mainly sourced from the state of Vermont. Many of the original slate quarries in the US no longer exist. Slate production peaked in 1900 but declined as asphalt shingles became common. Due to their longevity, slate roof shingles continue to be in demand.

Advantages of Slate Shingles

  • Longevity:

Due to slate’s durability, a slate shingle roof can last up to 100 years and more. There are many roofing manufacturers that over a 100-year warranty for their slate roofs.

  • Durability:

Since slate is a natural stone, it is very durable. Its high-density makes it very good at waterproofing since it will not absorb water.

  • Non-combustible:

Slate is non-combustible and hence fire-resistant. Therefore customers can rest assured that their roofs will protect their home.

  • Weatherproof:

Slate roofs are resistant to temperature fluctuations. This makes them ideal for customers living in areas prone to extreme weather.

  • Low-maintenance:

A slate roof can last 100 years or more. The integrity of slate shingles is not impacted by fungus or mold.

  • Increase in Home Resale Volume:

Using slate shingles for roofing instantly increases the property’s resale value due to its durability and aesthetic appeal.

Disadvantages Of Slate Shingles

  • Fragility:

Slate is durable but can be damaged if stepped or walked on. Once the slate shingle is damaged, it can difficult to replace since it is almost impossible to find a perfect replacement. (Shingles are generated in lots from natural stone and each lot is different, which makes it nearly impossible to find replacement tiles that are a perfect match.)

  • Weight:

Slate shingles can weigh between 800 to 1500 pounds per 100 square feet. Some roofs may require additional structural support to bear the weight of the slate roof. Therefore, it is important to have the property evaluated from a structural standpoint prior to investing in a slate roof.

  • Installation:

The key to slate roof longevity is in proper installation. Slate roofs need to be installed by contractors that have extensive experience. If a slate roof has not been installed properly, it can cause many roof problems and additional costs.

  • Costs:

Slate roofs can cost anywhere from $1000 to $4000 per square, almost five times that of conventional roofing materials.

Alternatives to Slate Shingles

Fiber Cement Slate

Fiber cement slate is a cheaper alternative to a natural slate shingle. It looks like natural slate. Fiber cement slate roofs are expected to last only 30 years on average and therefore homeowners would need to replace their roof sooner.

Concrete Tiles

Concrete tiles are known to last anywhere between 30 to 50 years. Concrete tiles offer waterproofing but are heavy. They are at least double the weight of natural slate per square meter. Concrete tiles also come with higher maintenance and handling costs.

Clay Tiles

Clay tiles are generally kiln-fired and last longer as compared to fiber cement slate and concrete tiles. They are known to last anywhere between 50 to 70 years. Clay tiles are fire-resistant and do not rot. Clay roof tiles are durable but very heavy and roofs that use them require additional support.

Ratings

Laboratory testing was conducted under the guidance of the National Slate Association to identify the ability of natural roofing slate to withstand hailstorms. North American produced S-1 rated natural roofing slate was used for the test. Slate at ⅜” and ¼” thickness was tested. The slate shingles were required to withstand two direct hits at the same point by ice balls fired from a compressed launcher at two different locations on the slate shingle. The ⅜” thick slate met Class 4 requirements, withstanding the impact of 2” ice balls at a speed of 76mph. The ¼” thick slate met Class 3 requirements, withstanding the impact of 1 ¾” ice balls at a speed of 69 mph.

The National Slate Association and National Roofing Contractors Association teamed up to conduct fire resistance testing on a slate roofing system. The test comprised of ¼” thick North American slate shingles laid with a 3-inch headlap over No.30 felt underlayment on a ½” plywood roof deck. Class A rating was achieved.

Slate shingles are non-combustible, slip resistant and impermeable to water naturally. Their colors don’t fade and the shingles are not affected by extreme fluctuations in temperature. Slate shingles are also impervious to chemicals.

Solar Reflectance

Natural slate shingles contribute to decreased utility costs and reduce energy consumption. Slate roofing can reduce the urban heat island effect provided the solar reflectance index of the surface is sufficient. High solar reflectance index roofs offer energy savings between 10-30% for average daily summertime loads as well as peak summertime loads.

Pricing

Slate roofs can cost anywhere from $1000 to $4000 per square.