SLATE ROOFING

Slate offers you a lifetime roof with premium elegance and beauty. This slate roof comparison post explains options, explores pros & cons, details the cost to buy and install slate roof tiles and also looks at the main suppliers of slate roofing as well as slate roof alternatives.

OVERVIEW
OPTIONS
PROS & CONS
COSTS
SUPPLIERS
ALTERNATIVES

Let’s start with the bottom line. Genuine slate roof cost is $14.50 to $28.00 per square foot based on material and installation factors. Those factors are discussed below.

WHAT IS SLATE ROOFING

Slate is a metamorphic stone that splits easily to form roof tiles. Minimal processing is required, which means little energy is used to make it. Combined with its longevity, slate is one of the most ecofriendly roofing materials available.

Slate is mined throughout the world including the US. Slating is the term used for slate roofs. Installers are called slaters.

For most installations, holes are drilled into the top of each tile, and the tile is fixed with copper nails with large heads. Stainless nails are sometimes used too.

This is steep-slope roofing. A pitch of at least 8:12 is preferred, though with specialized installation, slopes as low as 4:12 can be slated. Steeper roofs shed water better and more easily keep out wind-driven rain.

SLATE ROOF TILE OPTIONS

When shopping for a slate roof, you’ll have these considerations.

Colors

Shades available are grays ranging from pale to quite dark plus rose, purpose, greens, blue, brown and black. Specific color is determined by the level of iron and organic matter in the rock. The name of the slate often includes its source location – Vermont Purple or Brazilian Black, for example.

Colors used for a roof can be uniform or mixed. Some installations use differing colors to produce patterns and mosaics.

Shapes

Not all slate roofs look the same.

The rock can be cut and installed in various ways to create different styles.

• Uniform: Common in the US, the slate tiles are cut to uniform length and width to produce a very orderly roof with straight horizontal lines and staggered vertical lines.
• Variable width: Slate tiles of varying widths but uniform length create a roof with straight horizontal lines but very random horizontal lines.
• Staggered butt: Both lengths and widths vary creating an Old World look.
• Ragged butt: Tiles have jagged exposed ends. Widths can be uniform or varied.
• Rounded butt: The lower end of each tile is rounded to produce a scalloped look. Rounded slate tiles cost more due to the enhanced processing required.

Tile Dimensions

A wide range of tile sizes are produced. At the small end are tiles about 12”x6” that require more than 500 tiles per roof square (100 sq. ft.). The largest tiles are about 24”x12”, and when necessary overlap is factored in, about 120 tiles are installed per square.

Grades and weight

Thickness affects the hail rating of tile, and generally its impact resistance. Weight affects installation costs. Heavy tiles require additional bracing in the roof structure before the material can be installed.

• Standard grade tiles are 1/4″ thick and weigh 650 to 800 pounds per square.
• Standard rough texture tiles are 1/4″ to 3/8” thick and 650 to 1,000 pounds per square.
• Architectural tiles are the heaviest commonly used in residential applications. They are 3/8” to 1/2″ and weigh 1,200 to 2,000 pounds per square. Most roofs can’t take them without fortifying the structural framing.
• Heavy grade and Estate grade slates are 1/2″ to 3/4″ thick with weight up to 2,200 pounds per square.

Some slate roofing features tiles of differing thicknesses to produce a varied profile.

Slate is also graded by ASTM standards – S1, S2 and S3 – based on the hardness of the slate itself.

An S1 rating is the highest. According to the ASTM, S1 roofs last a minimum of 75 years, and 200 years is not uncommon. Most roofing slate is S1 rated.

PROS AND CONS

Slate is considered the most elegant roofing material, yet it accounts for a low percentage of roofs. The reasons for that are found in its advantages and disadvantages.

Slate roof pros:

Classic good looks

A slate roof is distinctive, utilizing the beauty of natural stone in a myriad of shades. The slate tiles can be uniform, randomly arranged or installed to create custom designs.

Durability

Standard grade tiles are backed by a 40-year warranty, though many roofs made with 1/4” tile last 80+ years. Thicker tiles are often warrantied for at least 50 years and can be expected to last more than 100 years with occasional repair and maintenance.

Impact resistance

Most, but not all, S1 slate tile has a Class 4 impact rating, the highest given to residential roofing. Tile must not crack when a 2” steel ball is dropped from 20 feet to pass the Class 4 impact test.

Fire resistance

Rock won’t burn. It’s that simple, so slate is a good choice where wildfires and forest fires are a threat. Keep in mind that slate roofs, like metal roofs, also trap heat and noxious gas from fire inside a home. Firefighters have a difficult time penetrating slate to allow these dangers to escape.

Waterproof rock

Slate’s very low water absorption rate makes it an ideal roofing material – it is essentially waterproof. It does not require sealing, as clay and concrete tiles do. While the slate is impervious to water, proper underlayment and water barrier in valleys must be used to make the roof system resistant to moisture.

Low maintenance

A slate roof should be inspected annually for damaged tiles, which are not common. If moss, algae or debris builds up on the roof, it can be removed with a power sprayer. That’s the extent of maintenance required.

Environmental friendliness

Natural slate tiles have the least embodied energy – the energy used to manufacture the roofing – of any roofing material. It is long-lasting and can be repurposed if it is removed from the roof.

Good resale value

For all the reasons above, a slate roof will help you sell your home. Potential buyers know they won’t have to worry about a new roof for decades to come.

Slate roof cons:

High cost

This is the most obvious factor in choosing another roofing material. Slate costs two to six times other roofing options.

Bad installation issues

Faulty techniques and workmanship lead to water leaks that can destroy the roof deck and cause water damage to the rest of your home. Only get estimates from experienced slaters with a proven track record of quality installation. They are few and far between, and that raises the cost to install a slate roof.

Structural support may be required

Slate roof contractors should be able to tell you whether your roof structure can support the weight of the slate you’re considering. Your building department might require an inspection by a structural engineer before granting you a permit. If bracing is required, expect a cost of $1,500 to $3,200 for most homes.

Fragility of cheap slate

Slate with less structural integrity is impossible for the lay person to detect. It can be brittle and easily broken by moderate-sized hail and falling branches that wouldn’t harm asphalt shingles or metal roofing.

SLATE ROOF PRICES

Cost to have a slate roof installed is $14.50 to $28.00 per square foot. The nearly 100% difference between the lowest and highest prices is consistent with other roofing materials including asphalt shingles, metal, clay tile and wood shingles and shakes. There are many cost variables, and they are detailed below.

How is $14.50 to $28.00 per square foot spent on a slate roof?

We’re going to unpack this for you in detail, but the general breakdown with price factors looks like this:

Slate tiles: $4.65 to $7.75/sq. ft. based on the thickness, quality, color and scarcity of the specific slate type.

Installation Accessories and Supplies: $2.65 to $4.40/sq. ft. for proper underlayment, water barrier in the valleys, trim and other features. Copper flashing and nails are typically used.

Labor: $9.00 to $16.00/sq. ft. based on the experience of the crew and the slope and complexity of your roof.

Other costs: Shipping costs, tear off of an old roof and structural support that might be required to support slate can add $15,000 or more to the total cost.

This slate roof price guide also includes information on the US distributors of slate mined here and around the world and the products these distributors offer.

SLATE ROOF TILE COST FOR MATERIALS AND INSTALLATION

This table details cost.

That’s an expensive roof. Many homeowners assume the profit margins must be quite high.

In fact, the pure profit on a slate roof is typically less than 10%. A huge percentage of the labor rate and markup on slate tiles goes to wages for skilled slaters at $15-$25 per hour, worker’s compensation for employees, various insurances including liability, vehicles, equipment and tools. Travel time can also be costly, since slate crews often travel significant distances to jobs.

Beyond the slate contractor’s overhead, here are factors affecting the itemized line costs in the table above.

Slate Quality

The cost of slate roofing tile is $4 to more than $9 per square foot, though most residential slate tile ranges from $4.50 to $7.75. Thickness is one variable, but quality is the more important factor.

US and Canada-sourced slate is of consistently high quality. If you buy imported tile, be sure that it has an S1 rating and has passed additional ASTM testing for strength and durability.

The International Association of Certified Home Inspectors (InterNACHI) has issued warnings against cheap slate, especially from China, Spain and Brazil, though not ALL slate from any of those countries is inferior. Slate with a high carbon content is weak and brittle. It also suffers damage in the freeze/thaw cycles common to northern climates. Carbon is seen as dark veins, spots or occlusions, and the slate is often brown or black in color. Do your due diligence to determine the source, quality and test ratings of the slate you put on your home.

https://www.nachi.org/slate-roofs-part2-121.htm

Quality of the Accessories

Slate lasts 100+ years, but if installers cut corners on underlayment, moisture barrier in valleys and on eaves and rakes or other essential accessories, you’ll have to replace the roof much earlier. Ask slate contractors about the type and quality of the accessories they intend to use, and choose premium accessories.

Tile Size

Larger tiles cover more area per tile, so require less labor per square. This lowers installation cost.

Color

Some colors are rarer than others and are sold at premium prices. Generally, gray/green colors cost least. Reds are usually the most expensive. Using a mix of colors is a common practice that will impact material costs. It might also affect installation cost because sorting and mixing colors on a roof takes more handling time than roofing with a single slate color.

Roofscape Complexity

This is the main factor in labor cost. The simplest roof to install is on a rectangular, single-story home with gables and few projections that have to be worked around. Aspects that increase installation cost are anything that makes installation more difficult or requires more slate tile cutting. These include dormers, chimneys and wall projections, very steep slopes, multi-story homes and homes with more than one roof level.

Your Location

Where you live affects slate roof costs several ways. Slate is mined in the northeast in the US. Imported slate arrives on the coasts and through Mexico. The further you live from where the slate is sourced, the higher the shipping rates will be. Secondly, the general cost of living in your area will affect slate roofing labor cost. Finally, competition among installers is a cost factor. Where there is little competition, costs are higher.

SLATE ROOFING COMPANIES

There are a handful of large slate distributors in the US. Some mine and fabricate their own slate tiles. Others purchase raw slate and turn it into roofing tiles.

Those that fabricate slate tiles mine their own slate, import bulk slate or both. From the mined slate, they split and cut it to a variety of tile sizes and punch/drill holes used to fasten it to the roof deck or battens.

Most sell full-size slate tiles that overlap several inches to prevent moisture and driving rain from getting beyond the tiles into the framing of the roof. One exception to that manufacturing approach is GAF TruSlate. It is a complete roof system with a waterproof underlayment that allows for minimal tile overlap, which results in less slate used and lower costs.

The companies in the following list sell traditional slate roofing rather than a modified design like TruSlate. Here is an introduction to each with information about the slate roofing products it sells.

Vermont Slate Company

This company is the largest distributor of slate tile in the United States. All Vermont Slate Company tiles are S1 rated and meet or exceed ASTM C-406 specifications for roofing slate. The company site provides ASTM testing information for the water absorption rate and rupture-point on most slates.

The company sells several slate lines mined in North America, with the State of Vermont being the largest source. The color range covers most available slate tones including the well-known Vermont Unfading Green and Unfading Gray in several hues.

Vermont Slate also distributes Cuppa Pizzaras slate, which is world-renowned material from 16 quarries in Northwest Spain.

https://vermontslateco.com/products/roofing-products/

American Slate Company

This is a subsidiary of Vermont Slate Co. but with a different, more limited lineup of slate products. American Slate Co. buys raw slate and fabricates it into tiles of various size and thickness. It currently offers 12 slate types. Most are from North America.

http://www.americanslate.com/natural-slate-roofing/

Evergreen Slate Company

This is another Vermont-based slate company. Evergreen Slate and American Slate are the two suppliers of slate to ABC Supply Company, one of the largest distributors of building materials in the US. It’s roofing tiles meet or exceed applicable ASTM testing and are rates S1.

Evergreen Slate Co. currently has 14 slate roofing colors available. Most are from the US or Canada. Like the other companies, Vermont Slate also offers color blends – tiles from several slate quarries.

http://www.evergreenslate.com/slate-colors-roofing.ASPX

Virginia Slate Company

Virginia Slate quarries much of its own slate, though buys some material from other sources. It fabricates the slate to standard and custom specifications to meet ASTM and S1 test standards.

The selection from Virginia Slate Co. includes 12 lines of slate quarried in Vermont plus 6 others mined in domestic or foreign quarries.

http://www.evergreenslate.com/slate-colors-roofing.ASPX

Vermont Specialty Slate

It’s easy to see that Vermont is the leading source for domestic slate production.

Vermont Specialty Slate fabricates new slate roofing tiles but also sells salvaged tiles. Eight slate tile colors are produced including the most popular colors Unfading Green, Semi-weathering Green and Unfading Red. A good selection of standard and custom tile dimensions are offered.

California Slate Company

This is another subsidiary of the Vermont Slate Company, and it serves the western US.

California Slate offers some of the same products as Vermont Slate but with the addition of several slate tile products from Asia. Two tiles meet SRI solar reflective criteria for certified cool roofing.

https://californiaslatecompany.com/

SLATE ROOF ALTERNATIVES

Several manufacturers have sought to capture the timeless good looks of slate but at a lower cost. You have four main options.

Composite slate

DaVinci slate, Ply Gem Engineered slate and EnviroSlate are materials made from plastics, elastomers and fibers. CertainTeed Symphony slate has been discontinued. A large percentage of recycled content is used in faux slate tiles. Composite slate weighs about a third of standard 1/4″ slate, is easier to install and has zero maintenance needs. Warranties range from 30 to 50 years. The downside is that composite slate can look like plastic upon close inspection. Composite slate cost is $8.50 to $11.00 per square foot.

Metal slate shingles and panels

Tamko MetalWorks, Classic Metal Roofing Systems and CertainTeed Matterhorn and Presidio are among the best, but not the only, lines of metal roofing stamped to look like genuine stone slate. The core is either galvanized steel, galvalume steel or aluminum. Kynar, Hylar and proprietary coatings are used.

Copper slate roofing is also available, though at the upper range of cost. Lighter weight, energy efficiency and lower cost are the advantages. Warranties range from 25 years to Lifetime. Some recycled materials are used, and it can be recycled when removed. Disadvantages are that the roof is metal, so doesn’t have quite the elegant appearance of natural slate. Metal slate roofing cost is $8.00 to $12.50 per square foot.

Rubber slate

EcoStar Majestic and EuroShield Heritage are the two top brands of rubber slate roofing. Recycled EPDM, TPO and other rubber-like materials are used to formulate the faux slate roofing. Rubber roofing resists damage from weather and impact. It can be recycled when removed. It lacks the beauty of real slate, but costs a lot less. EcoStar has a 50-year warranty. EuroShield warranty is Lifetime. Rubber slate cost: $8.75 to $11.00 per square foot.

Ceramic slate

Ludowici is a leading manufacturer of clay roof tile. Its LudoSlate is a ceramic alternative to genuine tile. The material is backed by a 75-year warranty and weighs about 600lbs per square, slightly less than 1/4″ roofing slate. It’s the most expensive alternative slate at $11.50 to $14.00 per square foot.