Slate to concrete
Can you replace slate with concrete tiles?
The short answer
Often yes, though it counts as a new covering rather than a like-for-like fix. A concrete tile has its own weight, its own minimum pitch and its own batten spacing, so the rafters and the roof angle are checked first. Where the house is listed, or stands in a conservation area, phone the council before ordering tiles. A departure from slate may be refused.
What a switch from natural slate to concrete interlocking tiles involves, what it can cost you in consents, and when keeping the slate is the simpler route.
Why swapping the covering is a bigger job than a repair
Putting a slate back where a slate was is maintenance. Putting concrete where slate was means a new covering, and new rules come with it. The products sit differently. A slate is small, thin and overlaps its neighbours. An interlocking concrete tile is large, locks sideways into the next one and is laid to its own batten gauge. So the battens come off with the slates, and fresh ones are cut to suit whichever tile you choose.
The look changes too. Slate has a fine, flat texture and a slightly varied colour. Concrete reads from the street as a heavier, more even surface. Some owners prefer that. Others find it flattens a house that was designed around slate. On a Victorian or Edwardian terrace the difference is obvious from the pavement, which is why councils take an interest. We would rather you saw the finished roof on paper than found out once the scaffold is down. Our slate roofing page covers the wider picture.
Rafters, weight and the building control question
For weight, the Planning Portal draws its line at 15 per cent extra on the roof covering, and approval is needed at or beyond it. It also suggests an engineer or surveyor takes a look whenever the new tile differs a great deal in mass from the old. Approved Document A treats a rise of over 15% as a significant change in loading. Your rafters were sized for slate, so they get examined before a different tile goes on. The weight of the old slates is the baseline for that check.
Energy rules are a second trigger. Part L can apply once more than 50 per cent of the roof is renovated. For work that normally needs no application, the Planning Portal sets limits of less than 25 per cent of the building envelope and less than 50 per cent of the roof. Arun's building control team counts new coverings on pitched and flat roofs as approval work, so describe your job to them, or to a registered building control approver. See re-slating and the Building Regulations for the usual route.
Planning permission, listed roofs and conservation streets
A like-for-like re-cover seldom needs a planning application, because the elevations stay as they were. Moving from slate to concrete alters the material, and that is where the caveats start. For a listed house, listed building consent governs any alteration to the features that earned the listing. A conservation area, or a house caught by an Article 4 direction, may carry limits of its own.
Arun's appraisal of Aldwick Road records many slate roofs there that now wear modern concrete interlocking tiles, and it says the street scene loses out. Its remedy is to put original roofing back. The Steyne entry in that document asks for slate or plain clay tiles to return wherever modern material was fitted instead. In those streets a planning officer is more likely to steer you towards slate than away from it. Read our notes on a slate roof in a conservation area, then take it up with the planning officers at Arun.
Pitch and fixings for the new tile
Each concrete tile has a minimum pitch published by its maker. Marley's interlocking profiles run from 12.5 degrees up to 25, and its concrete plain tile needs 35. BS 5534 puts natural slate at 20 degrees for a 500 mm slate in moderate exposure. A shallow slate roof can often take an interlocking tile, and a steep one can take nearly anything, but the manufacturer's data sheet settles it, not a rule of thumb.
The fixings change as well. Slates hang on nails or hooks. A single-lap tile such as an interlocking concrete one needs at least one mechanical fixing, as Wienerberger sets out, and ridge, hip and verge pieces are fixed mechanically rather than trusting mortar alone. Underlay, eaves ventilation and flashings are all re-measured against the new covering, because a flashing dressed to a thin slate edge does not always suit a thicker tile. Each of these gets a photograph on the roof itself, so you see what was found before you agree to anything.
When keeping the slate is the better call
Slate is a long-lived material. CORC reckons maintained slate can pass the 100-year mark, while Marley expects about 60 years from a concrete tile and stresses it is no warranty. A roof failing in patches, from slipped slates, a few cracked ones or tired nails, is often cheaper to repair than to strip. Our comparison of slate against tile goes through the trade-offs, including what each covering asks of the person who owns the roof over the decades.
Where the slates really are finished, new natural slate or an artificial slate keeps the original character and sidesteps the consent questions above. If a change of covering is what you want, we explain the consent route, notify building control where the work is notifiable, and send our quote in writing as a single sum after the survey visit. Whichever way you go, the diagnosis comes first and the reasoning with it, and the figure follows.
Related questions
Slate to concrete questions
Can the old slate battens be reused for concrete tiles?
Rarely. The new tile sets the batten spacing, so the old battens are measured against it and usually renewed as the slates come off. The rafters underneath are inspected at the same time, since the new covering has a different weight.
Will a concrete roof leak less than a slate one?
Not by itself. Either covering sheds water when it is laid at the maker's pitch over sound underlay with well-dressed flashings. Leaks tend to start at valleys, abutments and chimneys, so the covering is only part of the answer.