If you own an older home in Northeast Ohio, there’s a fair chance it still has its original slate. Sooner or later someone will tell you it “needs a new roof.” Sometimes that’s true. Often it isn’t. Here’s how to tell the difference.
How long slate lasts depends on the kind of slate
Slate is stone, but it isn’t all the same stone. The National Park Service’s Preservation Brief 29 says a properly installed slate roof will last 60 to 125 years or longer, depending on the type of slate, the roof’s shape, and where the building is. Some slates have lasted more than 200 years.
The Brief gives rough figures by source:
- Vermont and New York slates: about 125 years
- Buckingham (Virginia) slates: 175 years or more
- Pennsylvania Soft-Vein slates: in excess of 60 years
- Pennsylvania Hard-Vein and Peach Bottom slates (no longer quarried): roughly 100 and at least 200 years
The Brief calls these a general guide only. The National Slate Association gives similar figures.
Slaters usually boil this down to hard slate and soft slate. Joseph Jenkins, author of the Slate Roof Bible, puts it plainly: hard slates should last the life of your house, while with soft slates you may not have a choice and may have to replace the roof. So the first question isn’t “how old is my roof?” It’s “what kind of slate is on it?” An 80-year-old hard Vermont slate roof may have decades left. An 80-year-old soft slate roof may be near the end.
Problems that are usually repairable
Most leaks on old slate roofs aren’t caused by the slate. They come from the parts around it. Preservation Brief 29 notes that when damage is caught early, “the roof can usually be repaired or selectively replaced.” Common repairable problems:
Broken, cracked, or slipped slates
Falling limbs, ice dams, foot traffic, or a natural flaw can crack a slate. A slater pulls the broken piece with a slate ripper and slides in a matching one.
Rusted nails
A slate that slides out of its course is often the nail’s fault, not the stone’s. The NPS calls rusting of nineteenth-century cut nails “a common cause of slate loss on historic roofs,” and notes that plain steel and galvanized nails usually rust out long before the slate does. When nails are the problem, many of the slates can often be saved and reused.
Worn flashing
The Brief calls flashings “the weakest point in any roof.” Chimney, dormer, and vent flashings can be replaced without touching most of the roof.
Copper valleys and gutters
Valleys and built-in gutters carry more water than anything else on the roof. Pinholes, split seams, and worn-through metal are common. Re-lining a valley or built-in gutter is real work, but it’s a repair, not a new roof. The NPS recommends heavier copper (20 or 24 oz.) for gutters and valleys.
Bad past repairs
Tar, face-nailed patches, and mismatched pieces can usually be redone correctly. Whole-roof coatings are much harder to undo, so avoid them.
Signs replacement may really be warranted
Sometimes patching just throws good money after bad. Watch for:
- Widespread delamination and flaking. As slate weathers, thin layers flake off and the stone turns soft and spongy. The NPS notes that a sound slate gives a clear ring when tapped, while badly weathered slate gives off “a dull thud.” Weathered slate is usually just as bad on the underside, so it can’t be flipped over and reused.
- Soft slate at the end of its life. If the roof is soft slate and it’s flaking and crumbling across most of the surface, repairs won’t buy much time.
- Lots of slates failing at once. Preservation Brief 29 says that if 20% or more of the slates on a roof or roof slope are broken, cracked, missing, or sliding, it is usually cheaper to replace that roof than to repair slates one by one. Often only the worst slope needs it.
Even when replacement makes sense, it doesn’t have to mean asphalt. The NPS advises replacing deteriorated historic slate roofs with new slate, and sound slates salvaged from the old roof can go back on to match.
Ohio winters: freeze-thaw and ice dams
According to the NPS, frost and temperature swings mostly do their damage after a slate has started breaking down chemically, so weathered slate goes faster in a climate like ours. Eaves and valleys, where water concentrates and ice dams form, tend to wear out first. Ice backed up in gutters and valleys can crack slates and push water under them.
Check eaves, valleys, and gutters after a hard winter. The Brief also notes that a common copper-strip slate repair isn’t recommended for northern climates, because snow and ice can bend the tab and let the replacement slate slide out. In Northeast Ohio, how a repair is done matters as much as whether it’s done.
Keep “roof walkers” off your slate
A lot of slate damage comes from people walking on it: roofers, gutter cleaners, chimney sweeps, installers. A boot heel can crack a slate that won’t break off until the next freeze.
The Slate Roofing Contractors Association of North America (SRCA) states it directly in its repair guidelines: “Workers shall not damage slates by walking on them.” It calls for roof ladders, hook ladders, lifts, or similar equipment. The NPS likewise recommends ladders hooked over the ridge. If someone starts walking across your slate to look at it, that tells you how they’ll treat it.
For routine checks, the NPS suggests binoculars from the ground, yearly and after big storms.
Get it in writing before a big decision
Repair-or-replace is a big decision, so it deserves more than a look from the driveway. The SRCA’s guidelines say an evaluation should be done by someone experienced specifically in slate repair and restoration, and should cover the attic and deck, the slate type and remaining life, fasteners, flashings, and past repairs. They also say a correctly installed roof whose slates have reasonable life left, for example at least fifteen years, is a candidate for restoration.
A written condition assessment gives you:
- What kind of slate you have, and a realistic estimate of how much life it has left
- Which problems are repairable, and which areas (if any) truly need replacement
- Photos and notes you can use to compare contractor bids
- A record for maintenance planning, insurance, or a future sale
If you’d like a second set of eyes
If you’re weighing repair against replacement on a slate roof in Summit, Cuyahoga, Medina, Portage, or Lake County, our Historic Roof Condition Assessment (from $395) gives you a written report on what you have and what it needs. You can also read more about our historic and specialty roofing work, or call Forest Historical & Specialty Roofing at (440) 201-9844. We’re glad to talk it through, even if the answer is that your roof just needs a few slates.
Sources
- National Park Service, Preservation Brief 29: The Repair, Replacement, and Maintenance of Historic Slate Roofs: https://www.nps.gov/orgs/1739/upload/preservation-brief-29-slate-roofs.pdf
- Slate Roofing Contractors Association of North America, Slate Roof Repair, Restoration, and Maintenance Guidelines: https://slateroofers.org/downloads/Repair_Restoration_Guidelines.pdf
- Joseph Jenkins, Slate Roof Bible, 2nd ed., Chapter 1: http://www.jenkinsslate.com/downloads/SRB2_p1.pdf
- National Slate Association, Technical Bulletin No. 9: Common Myths About Slate Roofing: https://www.slateassociation.org/wp-content/uploads/2023/02/NSA_TECH-BULL_9_Slate-Myths-final.pdf
