Deciding what to do with a slate roof
A slate roof does not present a single decision. It presents three, separated by an order of magnitude in cost, and the right one is determined by the house rather than by preference.
Road one: repair what has failed
Correct when the field is sound and the failures are local — a run of slipped pieces, a valley at the end of its life, flashing around a chimney. Slate fails piece by piece rather than all at once, and a roof losing a few slates a year is not a roof at the end of its life.
The limiting factor is usually not the slate but the nails. When fasteners across the whole plane have corroded, individual repairs stop holding and the roof is telling you something. That is visible from the attic before it is visible from the street.
Road two: replace in kind
Costs several times a shingle roof and buys another century, and in this valley it is more available than almost anywhere else because the material and the trade knowledge are both local. Reclaimed slate of matching character can often be sourced within an hour of here.
The question that decides it is structural. Slate is heavy, and a hundred years of carrying it may have moved framing that was adequate when new. An honest assessment of the rafters and the deck comes before any quote for the covering.
Road three: change material
A legitimate choice, not a defeat — particularly where the structure will no longer carry the weight, or where a previous owner already replaced half the roof with something else and the argument for purity is gone.
What it changes: the deck almost certainly needs sheeting, since spaced boards were sized for a hung material. That is a real cost and it belongs in the quote from the beginning.
Quick answers
- How do I know if the slate itself is finished?
- Sound slate rings when tapped and resists a thumbnail. Slate near its end sounds dull and flakes at the edges. A roof where most pieces still ring is a roof worth keeping.
- Can slipped slates just be nailed back?
- They are re-hung rather than nailed through, using a hook or a strap. A piece face-nailed through the middle is a repair that creates the next leak.
- Does a slate roof need a specialist?
- For anything beyond a few pieces, yes. Slate is walked differently and broken easily, and a crew that works only asphalt will cause more damage than it repairs.
Next step: The slate came from down the road
Every slate roof is its own case. Use this to frame the conversation with a contractor, not to reach a verdict from the ground.