Is Horsham stone the same as slate?

Roofers describe many thin, flat coverings as slates, and Horsham stone is often called a stone slate. The name describes the job the piece does on a roof, not the rock it comes from. Checkatrade even covers stone slate within its slate roof pages. That overlap leads people to assume the two are one material at different prices, and a sales brochure that says slate without saying which kind does nothing to correct the impression.

They are not the same. Horsham stone is sandstone, cut and split into heavy slabs. Natural slate comes from a different rock that splits into thin, flat, even sheets, and Welsh and Spanish slates are the common imports. When you hear that a house has a slate roof, ask which kind, because the repair method, the supply and the permission route can differ. Our page on what Horsham stone roofing is explains the origin.

From the lane, the difference is texture. Slate roofs are crisp, with straight edges and an even thickness, laid in rows of matching size. A Horsham stone roof is rough and heavy-looking, and its slabs vary in size, outline and shade, with browns, greys and ochres weathering together. Courses shrink steadily from big slabs by the gutter to small ones under the ridge, a pattern known as diminishing courses.

A slate roof needs no such grading, because every piece is cut to the same few sizes, and that single fact explains much of the difference in labour. Since no two stone slabs match, a stone roof cannot be re-covered from a pallet of identical pieces. Each slab is chosen for its place, which is why stone work moves slowly. It is also why an old stone roof can often go back down using most of its own slabs, whereas a slate roof tends to be re-slated with new slates chosen to match the old.

Slates are normally nailed through a hole punched near the top of each piece, or held by hooks. Cupa Pizarras, a slate maker, points to BS 5534:2014+A2:2018, which indicates 20 degrees as the shallowest slope for a 500 mm natural slate in moderate exposure, and warns against hook fixings anywhere below 25 degrees. Those are slate rules, taken from one maker's advice.

Horsham stone is traditionally hung from battens on oak pegs or nails through drilled holes, a quite different approach, and the heavy slabs need a frame built to bear them. Stone follows its own traditions, and a roof built for one covering cannot be assumed to suit the other. Our answer on replacing a stone roof with tiles shows why any change of covering starts with a survey, and the same reasoning applies to a switch between stone and slate.

Both coverings sit at the long-lived end of roofing. CORC gives well-maintained natural slate 100 years or more, and Checkatrade's slate guide credits stone slate with over a century. Treat both as typical ranges and never as assurances: the fixings and the timbers beneath tend to tire long before the rock does, which is why a stone or slate roof is so often repairable instead of finished.

On price, Checkatrade's slate guide (its table is dated September 2026) lists £160 to £210 per square metre for a natural slate roof, averaging £184, and £95 to £125 for Spanish slate. It offers no separate Horsham stone figure to set beside them. Stone takes more hand sorting, so the cost depends on the roof as much as the rock. Those are typical national ranges, and your own total follows the survey and your own roof's size, access and condition.

On an existing roof, the answer is nearly always to repair in the material already there. A stone roof is mended with stone and a slate roof with slate. Mixing them changes how the roof looks, and on a listed building or in a conservation area that may need consent. The South Downs National Park Authority is clear that small repairs matching the original and done in place need no listed building consent. A swap to a different covering is not one of those.

If you are unsure which you have, the survey will tell you. We photograph the slabs, see how they are fixed and say plainly what the roof is, which saves guesswork when you later talk to a council, an insurer or a buyer's surveyor. Our guide on Horsham stone against sandstone, slate and reconstituted stone compares the options, and our slate roofing and Horsham stone roofing pages describe the work on each.