Why Slate Roofs Fail (Usually Not the Slate)
Natural slate doesn't wear out. The Welsh slates we fit today are the same quarry material that was put on Sheffield's Victorian terraces in the 1880s — and the ones still on the original roofs are mostly in excellent condition. What fails first is the fixing. The nails corrode through (iron nails last 80 years at best, copper nails last 150+), the laths rot, and slates start slipping one by one.
This is why you'll see a lot of Sheffield slate roofs where someone has re-hooked individual slipped slates with lead tingles. Tingles work, but they're a temporary fix — once a few slates have slipped, the underlying fixings in that whole area are probably close to failing. At that point, a full re-slate is more economical than doing tingles for the next ten years.
Individual Slate Repairs & Tingles
For a single slipped slate, or a handful in one area, a tingle repair is the right answer. We carefully lift the slates above, slide the slipped slate back into position, and secure it with a copper or lead tingle — a strip of metal bent over the bottom edge of the slate and clipped to the batten below. Done properly, it's invisible from street level and holds solidly for decades.
What we avoid is nailing directly through the face of an existing slate (it looks terrible and will leak within five years), or mortaring the slate down (the mortar breaks down faster than the slate and traps water). Tingles are the conservation-grade fix.
Full Re-Slating — When It's Time
If you're seeing regular slips — more than half a dozen a year — your roof is telling you the fixings have had it. At that point the choice is between patching individual slips indefinitely, or biting the bullet and having the whole roof re-slated.
A full re-slate means stripping all the slates down (salvaging the sound ones), removing the old laths and felt, fitting new breathable membrane over the rafters, new treated softwood battens or preferably 38x25mm laths, and re-laying the slates with copper nails to a proper headlap (usually 75–90mm depending on pitch). Ridges get re-bedded (or better, fitted with a dry ridge system), valleys are relined with code 5 lead, and flashings are all renewed.
On a three-bed Victorian terrace in Sheffield, a full re-slate with salvaged Welsh slates takes about 8 to 10 working days. With new imported Spanish slate it's the same timescale. The finished roof will look extraordinary — and will easily see out another 100 years of Sheffield weather.
Which Slate to Use
For conservation areas — Nether Edge, Sharrow, Broomhill — we'd almost always recommend salvaged Welsh slate or new Welsh from Penrhyn or Cwt-y-Bugail. The colour, thickness and riven texture of Welsh is what the building was designed for, and nothing else quite matches. The price premium over Spanish slate is significant but worthwhile on period properties.
For ordinary Victorian and Edwardian terraces outside conservation areas, Spanish slate from CUPA or SSQ (T1 grade — the top grade) gives you a visually similar finish at a noticeably lower cost, with a 75-year manufacturer warranty and no compromise on performance. Modern Spanish slate is a very different proposition to the cheap imports of the 1980s.
Synthetic slate — Cembrit, Eternit — has its place, usually on lighter-weight new-build or conversion projects where the roof structure won't take natural slate. We're honest about when it's the right answer and when it isn't. On a proper Victorian terrace, it's almost never the right answer.
Listed Buildings & Conservation
We do a lot of slate work on listed buildings and in Sheffield's conservation areas. Listed building consent usually requires like-for-like replacement with the same slate type and size, lime mortar rather than cement for bedding, and traditional fixings. We handle the liaison with the conservation officer, provide the materials specification to their standards, and keep dated photographic records of what's been replaced.
If your property is listed and you're not sure what's permitted, ring us before you get quotes from anyone. Work done without consent has to be reversed at the owner's cost — we've seen it happen. Getting the specification right first time saves a lot of grief.
