Question answered
Replacing a single stone slate
The short answer
A single stone slate can usually be replaced as a small repair, provided the new piece matches the old in size, thickness and weathering and sits in its proper course. The roof's own spare or salvaged stone is the first place to look. The slate is held on its fixing, not stuck down with mortar, and a listed building needs a check that the repair stays like for like.
One cracked or slipped slate on a Horsham stone roof is usually a small repair, but the replacement has to be the right stone, in the right course, held the right way.
Match the stone, not just the hole
A gap in a stone roof looks like a simple problem, but any slate will not do. Horsham slates run in bands of reducing size, so each piece belongs to a course of similar neighbours. A slate cut for the eaves is far too big for a course near the ridge, and one that is too small leaves a gap for rain to find.
Thickness matters as much as width. A thin replacement sits low and lets the slate above rock on it, while a thick one props up the course and opens a path for wind-driven rain. Colour and surface differ as well. Weathered stone carries lichen and a rough face, and a freshly cut piece can stand out for years.
So we measure the course before choosing, and offer the stone up to see how it lies before it is fixed. The size of the course sets the rule, and the stone follows it.
Where the replacement stone comes from
The Stone Roofing Association puts reuse first, so the roof's own slates are the ones to reach for. On your own house that often means taking a sound slate from a spot nobody sees, or from an outbuilding in the same stone, rather than buying in.
Where nothing suitable is to hand, the association discourages lifting slates off other buildings if there is any other route, because that trade strips other old roofs of their stone. If it cannot be avoided, the source should be checked to be legitimate. New Horsham slates are the better way to make up a shortfall, where they can be found.
Stone type needs watching as well, since the association keeps limestone slates apart from sandstones on the same roof. That is one reason to know what happens to old slates that come off a roof. A spare piece of your own stone is worth more than it looks.
Fixing it so it stays put
A stone slate hangs from its fixing on the batten and is held down by the weight of the course above. Fitting one means lifting the slates over it and sliding the new piece into line. It is fiddly because the neighbours are heavy, brittle with age and easily cracked by a careless lever.
The shortcut we avoid is mortar. Pointing a loose slate in place, or filling around a new one, traps water and stops the stone drying out. Horsham District Council's Steyning appraisal lists relaying slab roofs with mortared joints as poor repair, and the same logic holds for a single slate.
Where a repair needs more than one piece, or a slate slipped because the lath behind it has rotted, we look at the timbers and nearby courses before closing it up. One slipped slate sometimes points to trouble further along the roof. See Horsham stone repairs for the larger picture.
Listed buildings and hipped roofs
On a listed building, the South Downs National Park Authority says routine maintenance and minor repairs that match what is there, done in situ, do not need listed building consent. Alteration, or complete replacement of historic fabric that affects the building's character, does. The Adur & Worthing guide to listed buildings puts repairs in non-matching materials on the list of work needing consent. A piece of mismatched stone is just the kind of change that can tip a small repair over that line.
If you are unsure, ask the council's conservation team before work starts. A slate beside a hip needs extra care, because cut pieces and the neighbouring courses are tied together more tightly there. Hipped stone roofs have their own page in this section.
On any stone roof, a single replacement is a good moment to note what sort of lap the roof has, since that tells us how the nearby courses will be disturbed.
Safety and whether it is a one-off
Stone slabs are heavy, and a cracked one can slide without warning. Please do not climb a stone roof to lift a slipped piece yourself, and keep people and pets away from the ground below. If a slate has already come down, pick up the pieces carefully, because they may be worth keeping.
Once the roof has been looked at, there are two outcomes. If the fault is one slate, the repair is quick and the cost is small. If the stone is shedding in several places, swapping one at a time only postpones a bigger job, and our page on how long relaying a stone roof takes explains what that involves.
We tell you which of the two you have, showing you pictures of the roof itself, and the price then follows in writing as a single figure, so there is nothing to decode. The full range of work sits on our Horsham stone roofing page.
Lost stone slate queries
Can I use a clay tile to patch one missing stone slate?
It will keep water out for a while, but it looks wrong, sits differently on the batten and on a listed building could be read as swapping the material. A matching stone is the better patch, and the roof's own spare stone is the best source.
Why did a stone slate fall off a roof that looks sound?
Slates can split along their bedding, and the fixing or batten behind may have decayed even if the face looks fine. One that slips often says something about the timbers or the courses nearby, so the surrounding area is worth checking.
Tell us about your roof
Describe what is happening and we will call you back to arrange a visit.
- Photographs of what we find
- A written quote with one total price
- Or call 01903 299063
10-year workmanship guarantee, in writing.