Stone, hung on copper.
A slate roof is split stone hung on copper nails over sound decking. Done right, the slate outlives several sets of flashing and nails.
Hard and soft
Slate quarried in Vermont, New York, Pennsylvania and Virginia varies a lot in hardness. Hard slates last a century or more; softer ones flake and delaminate sooner. The slates themselves tell us which you have, and that tells us how much life is left.
Why we never walk on it
Slate breaks under a boot. We work from roof ladders, hooks and staging, which is slower and costs more, and is the reason your roof has the same number of unbroken slates when we leave as when we arrived.
When it’s time
When more than about a fifth of the slates are cracked, flaking or slipping across the roof, or the nails have rusted through broadly, a re-roof starts to make sense. Even then, sound slates are often salvaged and reused.
Slate prices.
A few slates down? That’s a repair.
The heritage roofing site, built in seven days.
Sixteen pages: three materials compared by lifespan, a repair-before-replace argument, ice dams explained for Maine, and Portland’s historic districts covered.