Replacing a slate in the middle of a roof presents a problem that does not exist anywhere else in roofing. The nail holes for that slate sit under the course above it. There is no way to drive a nail into the original position without lifting or breaking the slates covering it. The replacement has to be secured some other way, and the two honest answers are a slate hook or a nail set into the exposed joint above.
Which one gets used is not a matter of preference. It depends on the pitch, the exposure, the condition of the deck, whether the roof is visible from the street, and how many slates in that area are likely to need attention in the next decade. Both methods are correct in the right place and both fail in the wrong one.
If a roofer has told you there is only one way to do it, or if someone has stuck a replacement slate to your roof with a bead of adhesive, it is worth knowing what the real options are and what each one costs you in appearance and durability.
Why you cannot just nail a replacement slate
On a new roof, slates are laid from the eave upward. Each slate is nailed through two holes near its head, and the course above covers those holes. That coverage is what keeps water off the fasteners. Head lap, the vertical overlap between a slate and the course two above it, is typically three inches on a standard pitch and more on a shallow one.
When you remove a broken slate from the middle of an existing field, the courses above it stay put. You slide the new slate up into the gap and its head, with its two nail holes, disappears under intact slates. You cannot reach those holes, and you cannot lift the covering slates far enough to nail without cracking them, because slate does not flex.
Every replacement method is a workaround for that one geometric fact.
The slate ripper comes first
Before anything gets fastened, the old slate and its nails have to come out. The tool is a slate ripper: a long flat steel bar with a hooked, sharpened head and an offset handle. It slides up under the broken slate, hooks the shank of an existing nail, and cuts or pulls it when the handle is struck.
This matters more than it sounds. If the nails are left in place, the replacement cannot sit flat. It rides up on the old shanks, lifts the courses above it, opens the joints on either side, and creates a hump that catches water and ice. The visible symptom is a slate sitting proud of its neighbors, often with a shadow line under its tail.
A ripper used carelessly does its own damage. Struck too hard it cracks the slate above. Pulled at the wrong angle it splits the sheathing board. Careful slate roof repair work starts with getting the old fasteners out cleanly, because everything after that depends on the new slate sitting in the same plane as the field around it.
Slate hooks: how they work and where they belong
A slate hook is a short piece of stainless steel or copper wire, usually around three inches long, with a hooked end. The shank is driven into solid wood at the joint between the two slates below the gap, and the hook end projects up. The replacement slides up over the shank until its tail drops into the hook, which holds it against gravity and wind lift.
The advantages are real:
- Nothing penetrates the water plane in an exposed place. The shank enters a joint already covered by the slate above, so the fastener does not depend on sealant or a covering piece to stay dry.
- The slate sits flat. With no fastener under the head of the new slate, the replacement lies in the same plane as its neighbors and the head lap is undisturbed.
- It can be removed again. If that slate or one near it needs attention later, the hook releases without destroying anything. On a roof where more repairs are coming, that matters.
- It holds well on steep pitches. The steeper the roof, the more the slate’s weight loads the hook rather than trying to slide out of it.
The cost is that you can see it. A hook leaves a small metal tab at the tail of one slate. Stainless against gray Buckingham slate reads as a pencil line up close and disappears from the street. On a red or purple Vermont roof it is more noticeable. Copper hooks weather to dark brown and then green, which many homeowners prefer on an older house.
Hooks are the wrong choice on very shallow pitches, where the tail is not loaded hard enough into the hook, and where the deck at the joint is too soft to hold the shank.
Copper nails and the covering methods
The alternative is to nail the replacement through the exposed joint between the two slates above it, then cover that nail. Copper is the standard material. It does not corrode against wet wood, it stays soft enough to clinch slightly rather than split the stone, and it outlasts any galvanized product. Copper fasteners and flashings on a slate roof commonly reach the better part of a century, though that varies with exposure and with what drains across them.
The nail goes through the slot between the two slates of the course above, low enough to sit under adequate head lap, and into sound wood. The exposed head then has to be protected. There are two common approaches.
The copper bib
A small rectangle of copper, typically three inches wide and long enough to reach well above the nail, slides up under the course above so it covers the nail head and sheds water onto the face of the new slate. Nothing holds the bib but friction and the weight of the slates, so it has to be sized correctly. Too short and it does not cover. Too wide and it fouls the joints.
Done right, the bib shows as a thin copper edge at one joint and patinas in a season or two. Done wrong, it slides down and leaves a nail exposed directly over a hole in the deck.
The nail alone, in the right place
On steep roofs with generous head lap, an experienced roofer will sometimes set a copper nail in the joint without a bib, high enough that water running down the joint never reaches it in volume. That is defensible on a 12-in-12 pitch over a well-drained plane. It is not defensible on a shallow roof, in a valley, below a large catchment area, or under a chimney where water concentrates.
What is never acceptable is a nail covered with roofing cement. The cement fails in a few seasons, holds water against the copper and the stone, and makes the next repair harder. If you have seen black daubs on your roof, that is what you are looking at, and the slates around them usually need to be reset properly during a full slate roof restoration.
How we choose on a given roof
The pitch decides most of it. Steep roofs shed fast and load hooks well, so either method works and appearance becomes the deciding factor. Shallow roofs hold water longer in the joints, which argues for a nail set high under good head lap with a bib over it, because a hook on a shallow slope carries more shear and less clean vertical load.
The second question is how many more repairs that area will need. If the deck is sound and this is an isolated impact break, either method is a permanent answer. If the nails across that whole slope are near the end of their life, hooks make future work faster, because each one releases individually.
Then there is the house itself. On the older houses around Appomattox, where original slate roofs are still common, a front elevation with patterned or graduated coursing gets copper nails and bibs so the pattern is not broken by hardware. Rear and side slopes on the same house often get hooks, because nobody sees them and future access is worth more than appearance.
Exposure matters as well. Roofs on open ground take more wind uplift at the eaves and rakes. Around Altavista, where many slate roofs sit on exposed ridgelines, we tend toward hooks at the perimeter courses and bibbed nails in the protected field.
That is the ordinary decision-making behind slate tile replacement, and any roofer working on slate should be able to tell you which method they used and why.
Common questions
Will I be able to see slate hooks from the ground?
On most roofs, at most as a faint line. A stainless hook shows about a quarter inch of metal at the tail of one slate, seen from thirty or more feet below at a steep angle. Copper hooks darken within a year and read less than stainless on a weathered gray roof. If the repair is on a prominent front slope, say so before the work starts and we will plan around it.
Can a replacement slate be glued or caulked instead?
No, and the reason is not stubbornness about tradition. Adhesives do not bond durably to the face of slate, they are too rigid for a surface that expands and contracts daily, and they trap water at the edges once they begin to lift. A glued slate also gives no warning before it goes. A properly hooked or nailed slate that loosens usually slips visibly first.
How long should a properly replaced slate last?
As long as the slates around it, assuming the stone is a good match in thickness and quality and the deck holds a fastener. The replacement is not the weak point. The weak point is whatever caused the original slate to fail, and if that was a rotting deck rather than an impact, the new slate is a temporary answer.
Have a replacement slate checked before winter
If a slate on your roof has been replaced in the last few years, it is worth knowing whether it was hooked, nailed and bibbed, or simply stuck down. The first two will hold. The third will not, and it is easier to correct before the freeze-thaw season than after. Call +15555555555 to schedule an inspection.
