How Long Does a Slate Roof Last?
A properly installed natural slate roof lasts 75 to 150 years, but the stone is rarely what fails first. This video covers what usually goes first on Greater Boston slate roofs. Rusted nails lead the list. Chimney and sidewall flashing come next, followed by the valleys and the eaves. It also explains how hard and soft slate differ, and why an old slate roof is often a sound stone roof wearing worn-out flashing.
Lifespan: Art Slate site figure (75 to 150 years, properly installed natural slate). Flashing wearing out before the slate: National Park Service, Preservation Brief 29.
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Transcript
How long does a slate roof last? On a Greater Boston house, natural slate is good for 75 to 150 years. That's the number most homeowners come looking for. It's also only half the story. Because the stone is rarely what dies first.
On the roofs Arturo walks in Cambridge, Newton, and the South End, the lifespan is set by what's holding the slate, not the slate itself. Here's the usual order. First, the nails. Old iron or steel nails rust, and slates slip out of their course. Second, the chimney and sidewall flashing, where counterflashing loosens as the mortar ages. Third, the valleys, which carry water off two slopes at once. And fourth, the eaves, where ice dams push meltwater up under the first few courses.
The stone matters too. Hard slate, like Vermont and Buckingham Virginia, handles freeze-thaw well. Soft slate, like Pennsylvania ribbon, flakes and ages faster. Metal flashing often wears out before the slate does, so budget for flashing, not for new stone. Air-seal the attic floor and insulate first, keep the gutters clear, keep the eaves protected, and swap cracked slates promptly.
The mistake is assuming an old slate roof is a dead one. Often it's a good stone roof wearing worn-out flashing. Book a free, owner-walked assessment. Call 617-913-1130, or visit artslateroofing.com.