Known for its beauty and durability, slate has long been used in roof construction, adorning some of the world's most breathtaking historical structures, such as The Walt Disney Residence, Rockefeller Mansion and Oriel College at Oxford University. You most often find slate roofing on older historic buildings, along with institutional, government and ecclesiastical buildings, where longevity is essential. However, like all materials, slate isn't indestructible, meaning these roofs may occasionally need repairs.

With a large percentage of slate roof installations occurring during the late 19th and early 20th centuries, many of these roofs have begun nearing the end of their useful life. Though slate roof repair is possible, too many individuals employ improper repair and replacement techniques, sacrificing historic integrity and appearance of these buildings.

If you're lucky enough to have a slate roof, it's wise to know how and when to repair it. This comprehensive guide covers these important topics and other frequently asked questions about slate roofs.

What Is Slate and How Is It Made?

If you want to understand slate roofs, it helps to know a bit about slate, how it's made and its main characteristics.

Formation

Slate is a fine-grained crystalline rock formed under pressure through shale or mudstone metamorphosis. Through this process, the mudstone or shale comes under extreme pressure and heat resulting from tectonic activity, causing the clay minerals to metamorphose into mica minerals.

This rock is formed through foliation, or repeated layering in metamorphic rocks resulting from differing shearing forces or pressures. Foliation causes rock layers to form perpendicular to the orientation of the metamorphic compression pressure, enabling the slate to divide along flat planes. Each layer may range from over a meter thick to as thin as a sheet of paper.

Life Span

Slate quarried for roofing purposes is highly dense and durable, contributing to its long life span. Soft slate has a life span of approximately 50 to 125 years, while hard slates will last between 75 and 200 years, making it longer-lasting than most roofing materials. When broken, slate still maintains a natural appearance and remains flat and easily stackable.

Characteristics

Due to slate's varying mineral and chemical properties, you can find this rock in many colors, including green, blue, purple and red, as well as in numerous sizes and textures. Black slate gets its colors from carbonaceous matter derived from decayed marine life on the seafloor, while colored slates are shaded by iron compounds. These versatile and aesthetically pleasing compositions make slate ideal for creating stunning architectural effects for roofing applications.

Slate has a low water absorption index of less than 0.4%, making it resistant to frost damage. Slate is also a high-strength, low-porosity rock, so it's superior to roofing alternatives like wood and asphalt. On the Mohs scale, which measures a material's hardness, slate is ranked between 2.5 and 4 on a scale from one to 10, making it about as hard as marble or limestone but not as hard as natural granite or quartz.

Pros and Cons of Slate Roofs

While slate is a gorgeous roofing material with lots of exciting characteristics, it's not without faults. That's why it's important to consider both the advantages and disadvantages of slate roofs before deciding whether this material is right for you.

Pros of Slate Roofing

Slate has remained a popular roofing material for centuries for many reasons. Some of the primary advantages of slate roofs include:

• Appearance: Slate has a highly distinctive appearance that complements homes ranging from contemporary to historical, giving them a classy and timeless look.

• Longevity: With the proper construction and installation, slate roofing can last for over 100 years, outlasting even the building where it's installed. Its long-lasting use outweighs its higher installation costs.

• Variety: Because slate is available in various colors, sizes and textures, it allows homeowners to choose a configuration that best suits the style of their home.

• Value: Slate is an excellent investment, as its visual appeal, durability and longevity can boost your home's resale value, enabling you to establish a higher asking price should you choose to sell in the future.

• Protection: Due to its many unique properties, slate is highly resistant to fire, water, mold, fungus and insects, delivering continuous protection no matter where you live.

• Eco-friendliness: Because slate can survive over a century of use, it has a significantly lower environmental impact than other roofing materials. This material is also completely natural, meaning it can be recycled and harvested without disrupting the ecosystem. Slate is also free of plastics and chemical treatments.

• Minimal maintenance: Slate is a low-maintenance material, so slate roofs generally require nothing more than professional inspection and minimal upkeep every one or two years.

• Temperature regulation: Slate roofs are extremely dense with natural insulation properties that help maintain stable building temperatures, resulting in lower energy bills.

Cons of Slate Roofing

Despite its many benefits, slate also has a handful of disadvantages that homeowners should keep in mind:

• Cost: Though slate is a worthwhile investment, it has a high initial price that can cost several times more than other roofing materials.

• Fragility: While slate has many protective properties, this material is relatively fragile structurally. That means impact from a falling tree branch could result in expensive repairs.

• Weight: Slate can weigh up to 15 pounds per tile, ranging between 800 and 1,500 pounds per roofing square. This weight can result in structural strain, so some houses require extra reinforcement to support slate roofs.

• Installation: Improper slate roofing installation can result in significant issues, making it necessary to hire experienced professionals to do the job. Due to slate's heavy and fragile nature, roof installation can also be tedious and time-consuming.

Can Slate Roofs Be Repaired?

Yes, slate roofs can and should be repaired. It's vital to complete the proper repairs to cracked, broken or missing slates to prevent possible water damage, structural degradation and roof and sheathing deterioration.

Often, slate roofs are mistakenly replaced when they could have endured longer use with a few effective repairs. Hard slate, in particular, should be repaired in most cases. Because hard slate can last up to two centuries, a damaged slate roof may have well over 100 years of service life left in it despite its damage.

How Much Does It Cost to Repair a Slate Roof?

The cost of slate roof installation varies, depending on the building's size and pitch. Slate roof repair costs are typically a few thousand dollars per roofing square, with a large portion of this cost accounting for labor. Again, the total of a slate roof repair will depend on the roof's slope and size.

Should You Repair or Replace Your Slate Roof?

While completely replacing an existing slate roof that could have been salvaged is undoubtedly a loss, it's also detrimental to hold onto a slate roof that's at the end of its useful life. That's why it's vital to recognize when your slate roof needs to be repaired versus replaced. When you know what signs to look for, you can more accurately determine what kind of attention your roof needs.

Signs Your Slate Roof Needs Repairs

Even with the proper routine maintenance, the occasional slate repair is inevitable. Common signs that your slate roof requires repairs include:

• Cracks or breakage: Cracked slate is typically caused by impact from natural elements like tree branches or hail. Replace the cracked slate pieces with new materials.

• Missing slates: If you find that your roof is missing some slates, you can simply replace them.

• Fallen slate: If slate falls from your roof, pick it up and tap on the surface with your knuckle. If it produces a resonant sound, the slate is still in good condition and likely fell due to a loose nail.

Signs You Need a Slate Roof Replacement

If you find that 20% of more of the slates on your roof need to be replaced due to damage, it's best to replace the entire roof, as it's ultimately less expensive than paying to fill in all of the broken or lost slates.

Other signs you should replace your slate roof include:

• Flaking: Also called delaminating, flaking is a common sign of slate that's past its useful life.

• Powdering: If you notice that your slate has a powdery-looking surface, the roof will soon need to be replaced.

• Porousness: Even if your roof looks like it's in good condition, it may be worn beyond repair. If you tap the slate's surface with your knuckles and notice a dull thud, the material has likely grown porous and should be replaced.

• Moisture damage: When slate absorbs too much moisture, it becomes soft or brittle and can begin to rot, resulting in moisture damage in your home's rafters or attic.

Book a Professional Slate Roof Repair at Huber & Associates Today

You can seek high-quality slate roof repairs from the qualified experts at Huber & Associates. We've spent over 40 years delivering state-of-the-art roofing repairs and installations for even the most challenging projects. Our highly experienced team is dedicated to creating stunning solutions that last, accounting for all the necessary historical requirements and local codes to produce the most reliable results. Our extensive capabilities allow us to construct specially designed installations perfect for each homeowner.

Contact us to get started with our services today!