Slate roofing is a premium roofing material that looks beautiful and is one of the most durable materials on the market. Unlike asphalt shingles, builders have used slate roofing on historic buildings, residential homes, and businesses for centuries because its look is timeless, and slate tile retains its value better than most options. If you are an architect, designer, or ready to build your own home, slate should be a consideration when specifying a roofing material. It is fire and insect resistant, eco-friendly, and naturally sourced.
Here is an all-encompassing rundown of slate roofing, including an explanation of why slate roofing is important, how to install slate roofing, several beautiful examples of designs, and 5 helpful upkeep suggestions if you’re new to slate roofing.
What Is Slate Roofing (And Why Does It Matter)?
Slate roofing shingles are mined from the earth and represent one of the earliest roofing materials used as civilization began to expand across the globe. Slate develops as fine clay compressed by the weight of the earth, transforming it into shale and finally into slate.
The different stages of compression form the layers in a piece of slate that allows it to be split or sawn into different thicknesses. Usually harvested in large slabs, it is then sawn and quartered along the layers, or cleavage lines, until the desired dimensions are reached. The larger pieces are used for countertops, blackboards, electric panels and flooring. The smaller pieces are fashioned by hand or machine into shingles.
When choosing a roofing material, it’s important to know all of the options that are available. Asphalt shingle roofing may be the most popular, but that’s only because it is cheap to purchase and install.
Slate roofing is found on homes of distinction and would be the roof of choice for most people, if finances allowed. Slate is almost impervious to water, extremely durable, and is often called the Rolls Royce of roofing materials, or the lifetime roof. For most people, a slate roof will be their first and last roof.
The History Of Slate Roofing
The first recorded use of slate as a roofing material on a private home was in approx. 1300 A.D. in North Wales. Even then, it was expensive for most folks, and was mainly found on castles or military buildings. Eventually, it started being used in America around the 16th century, and the first quarry opened in 1734 on the border between Pennsylvania and Maryland. Still expensive, it wasn’t until the 1800s that slate became available to the average homeowner.
Slate is found in large quantities in India, Brazil, Asia, and the United States. In the U.S., it is mostly mined from Vermont, New York, Pennsylvania, and Virgina. The rock is taken from the quarry and sent to mills where it is inspected for defects before being manufactured into individual roofing tiles and other products.
The different colors in natural slate are present due to the mineral composition of each piece. Some contain more hematite, which produces purple highlights, while chlorite will give the shingle a green hue, and carbon gives the slate its trademark blacks and grays.
There are installations that require the use of both weathering and non-weathering slate tiles to get a more blended look when the roof is finished. This designation is determined by the amount of iron pyrite found in the slate. Iron pyrite is also called fools gold, and considerable amounts in a slate shingle can lead to it weathering to different shades of brown.
How Long Does A Slate Roof Last?
Slate is classified as hard or soft, and the difference determines how long it will last. Hard slate can last 75-150 years, while soft slate has a shorter lifespan of about 50-90 years. Of course, this depends on many factors, including: finished quality of the slate, installation, and how well the roof has been maintained. The origin of the slate is also paramount. Much of the slate mined in Vermont and New York is hard, while much of the soft slate is from Pennsylvania.
Generally speaking, slate does not come with a warranty because it is a natural product. The roofing contractor usually provides the warranty, so you need to ensure that your roofer provides a lifetime warranty and has been in business long enough for that to make sense.
Some aggressive roofing companies may tell you that your slate roof needs replacing, when simple maintenance is all that is needed. It takes years to become a professional slate roof installer with the knowledge to properly determine a roof’s condition. If the slate on your roof is less than 30 years old, consider having an inspector look at it first. It could save you a lot of time, money, and inconvenience.
The Pros And Cons Of Slate Roofing
As with any roofing material, there are pros and cons with a slate roof. We’ll review them in this section.
- Slate is a beautiful roofing material.
- It has a reputation for being used on the most admired dwellings.
- It is one of the most durable roofing tiles available.
- It is a natural product.
- It can be recycled as roofing again, making it eco-friendly.
- Slate is naturally fire-resistant.
- It is resistant to insect infestation.
- Slate is heavy. If you are building a new home, the roof must be engineered to carry the weight (up to 4 times as heavy as asphalt shingles).
- If you are putting a new roof on your existing home, you will need to have an engineer review your roof structure to determine if it will carry the increased weight. If the structure needs additional support, it can substantially impact the project's cost.
- A slate specialist will be needed for the installation. Regular roofing contractors are not qualified to install slate.
- Slate is strong, but it is brittle. Heavy objects (such as large hail) can cause damage.
- Slate roofing specialists will need to do the repairs since the same equipment will be needed to access the roof and complete the repairs.
- Slate is not easy to walk on and can be dangerous when wet.
There are options that can alleviate some negative aspects of natural slate roofing, and they will be discussed later in the article.
Traditional Slate Roofing Vs. Synthetic Slate Roofing
Natural slate roofing will not fit into every budget. However, you can enjoy the enduring elegance of real slate without the negative attributes. Composite roofing tiles are offered in plastic, rubber, and synthetic blends that can mimic the appearance of slate, and will also provide the following:
- They are lightweight. No additional support structure required on the roof.
- Easy on the budget. They can be installed by regular roofing contractors and cost less than slate.
- More durable than slate. Slate is strong, but it is brittle and subject to damage from falling heavy objects, as well as freeze/thaw cycles. Synthetic slate won’t break, crack, split or come apart because of extreme weather conditions. Synthetic composite slate tiles easily last 50 years.
- Huge color selection. Natural slate is normally offered in black and gray, with visible hues of green and purple. Synthetic slate is offered in many solid colors and blends.
6 Examples Of Slate Roofing Styles
With a hat-tip to Norwegian architecture, this barndominium is given a classic look with the addition of a brown-gray synthetic slate roof.
2. Light Arendale
French provincial design elements are complemented by a light gray composite slate tile roof. Notice the variations of shading that match the style of natural slate.
Black is the characteristic color of slate, and these composite tiles convey the look perfectly. They have rough-hewed edges, a mottled texture, and allow the grays to bleed through, producing the semblance of real slate.
Welsh slate is considered the finest slate in the world. It is quarried in Wales, which has a history of slate mining dating back 1,800 years. The blending of grays and purple gives this tile its unique appearance, and this synthetic roof is a showcase for the color blending capabilities of modern composite roofing tiles.
The typical dark tones associated with slate may not blend with your architectural scheme. Synthetic slate provides the option to choose almost any solid color or blend. A coffee-clay slate roof, otherwise unavailable from a quarry, can be shipped directly to your home, ready to install.
One of the enduring features of a slate roof is the mixture of dark and light grays that occur naturally as the stone is formed underground. This level of variation is impossible with rubber or plastic slate tiles. Synthetic composites are more advanced in their color technology and can perfectly match Mother Nature.
How To Install Slate Roof
Installing a synthetic slate roof is much less complicated than real slate, and can be done with tools available to most roofers.
Field Tile Layout
To begin the installation, ensure the roof deck is at least 15/32 in. CDX plywood or equal (4 ply is recommended where available). The following steps should be followed:
- Install appropriate underlayment, as well as ice and water shield flashing, per the manufacturer’s recommendations.
- The most common pattern is a straight line course of tiles, and this begins by installing the starter shingles at the roof edge. The starter tiles measure 12” x 14”.
- Locate the center of the roof and snap a line from top to bottom. Place a starter shingle on either side of the line with an overhang of 1” off the eave. Snap a line at the top of the course for reference and attach the rest of the row. Make sure to leave ⅜” between each tile. If a starter must be cut at the edge, place the factory edge to the outside.
- Attach the first regular tile centered over the center line and attach with two fasteners. Continue until the row is finished. Provide a minimum of ⅜” between each tile.
- Start the second row with a 6 ½” tile at the edge, set back 6” from the tile below. Repeat this alternating procedure (½” tile, full tile) until you reach the ridge.
Installing Tile At A Chimney
- Make sure all underlayment, ice and water shields have been properly installed before proceeding to the chimney.
- Install slates up to the base of the chimney.
- Install apron flashing to the chimney, so it covers the front and surrounds the sides above the next shingle line.
- Install minimum 6” counter-flashing at the front corners.
- Install the next course of slates. Do not nail in the flashing area.
- Continue installing slates and step flashings. Step flashing should overlap each other by at least 2”.
- Install a pre-formed metal cricket at the rear of the chimney, and continue installing slates, ensuring the flashing extends a minimum of 6” under the tiles.
- Install counter-flashing into saw cut reglets in the chimney to complete the flashing.
Installing Tile On A Hip And Ridge Roof
This section applies if you install hip and ridge roof:
- Start the installation as normal. When the row reaches the hip ridge, trim as close as possible to the ridge.
- When all the tiles are installed, install an 8” self-adhering membrane, centered over the ridge.
- Fasten hip slates using a 3” fastener on each side, placing the nails at the locator marks.
- The maximum exposure on each hip and ridge slate should be no more than 10”.
Installing Slates At Roof Penetrations
This section covers slate shingle installation at pipe penetrations:.
- Install tiles until you reach the base of the pipe.
- Attach the appropriate size flashing over the pipe and attach to the roof.
- Install the slates above the flashing sleeve, placing nails at the locator marks.
Installing Slates At Valley Locations
This section covers installation where two roof planes meet, forming a valley.
- Install 24-26 gauge corrosion-resistant flashing with a 1” center crimp.
- Flashing should extend 10” or more on each side for roof slopes 4:12 or greater, and 14” for slopes less than 4:12.
- As slates are installed, leave a 4” opening at the top of the roof, graduating ½” per 8’ as you move down the slope.
- For closed valleys (time 1:02 on video), a single 24-26 gauge corrosion-resistant flashing with a minimum 2 ½” center rib may be used.
- Cut the slates flush with the diverter.
5 Tips And Reminders For Slate Roofing Maintenance
If you’re installing a natural slate tile roof, you’ll need to be aware of the maintenance issues that might arise. Due to the high cost of the initial installation, the following steps should be followed to protect your investment:
- There should be an exterior visual inspection annually to check for cracked, broken, misaligned, or missing tiles. This should be done from the ground or with binoculars, a cherry picker, or a drone camera.
- Attention should be given to valleys, dormers, and chimneys, where flashing failure could be an issue.
- A slate roof can weigh more than 100 pounds per square foot, which puts a lot of pressure on your roof structure. You should make a visual check of the rafters in the attic a few times a year to ensure that everything is okay. Check for stains and wood rot that may be evidence of leaking.
- Check gutters and downspouts regularly to ensure they are clear and the water is flowing freely through them.
- Maintenance should only be performed by roofers experienced with slate tile installation. Improperly walking on real slate can cause tiles to break or crack, and pose a physical threat to those on the roof.
Slate Roof Cost - Analyzing How Much A Slate Roof Costs
There are a number of factors to consider when estimating the cost of installing a slate roof:
- Is your current roof engineered to carry the extra weight of real slate? If not, this could add thousands of dollars to the project. If you are building a new home, the architect or designer will need to make sure that slate can be installed based on the existing plans.
- Can you find an experienced installer in your area? Slate is expensive to install, and having a contractor come from out of town will increase the price.
- The cost of a slate roof can range from $1,200 to $3,300 per hundred square feet depending on the thickness, color, and durability. That is at least three times the cost of asphalt shingle roofing, and 2-3 times the cost of synthetic slate tiles.
Resources For Slate Roofing
Here are some other resources that can help you make a decision:
- The Slate Roofing Contractors Association maintains a list of reputable manufacturers and quarries on its website. You should also ask your installation company if it can reinstall or recycle your old slate, and adjust the price accordingly.
- The Slate Roof Bible
- National Slate Association
Slate is Good, But Synthetic Slate From Brava is Better
Natural slate is an excellent roofing material with centuries of architectural examples still standing today. Because of its reputation, curb appeal, and durability, slate is still in demand. However, with the rising cost of engineering, material, and labor, there is a better option for having a slate roof without the high cost and maintenance.
Brava Old World Slate is a premium synthetic roof tile that is durable, lightweight, insect-resistant and manufactured to look precisely like real slate. It has a 50-year warranty and a Class C or A fire rating, and Class 4 impact rating, the highest in the industry. Old World Slate won’t crack or split, and can handle weather extremes better than natural slate. Best of all, it is available in almost unlimited custom colors, including solids and blends.
Contact Brava today for free samples of our Old World Slate synthetic roof tile, and judge the quality for yourself.