Slate has a good name in roofing, and that has encouraged a whole family of look-alikes. When a quote says slate, it might mean thin layers of stone cleaved from rock in Wales or Spain, or it might mean a sheet of fibre-cement or composite pressed to resemble it. From the pavement the two can be hard to tell apart. Up close, and over a long stretch of weather, they behave quite differently, and those differences decide whether a swap is a sensible saving or a regret that shows from the street every day.
Choosing between them is rarely only about money. The covering sets how steep the roof must be, how much it weighs on the rafters, whether the council will agree to a change and how the house looks to the street. Below, each material gets its turn, with the figures that carry a published source and a short list of things to ask when someone proposes a swap. Our pitched roofing page covers slated and tiled roofs more widely.
What natural and man-made slate actually are
Natural slate is a metamorphic rock that splits cleanly into thin sheets. Quarries cut and trim the sheets into slates of a chosen size, and each slate keeps the marks of the rock it came from, including slight variation in tone, thickness and surface. Roofers in the south of England most often meet Welsh slate and Spanish slate, the two names that come up on quotes.
What counts as man-made slate?
Man-made, artificial or synthetic slate is a catch-all for manufactured slates. Fibre-cement slates are made of cement reinforced with fibres and moulded into slate shapes. Composite slates are cast from mixed materials, usually with a stone-like texture. Because each maker uses its own recipe, one brand's slate may differ from another's in more than price. Treat any general claim about man-made slate with caution until you have seen the data sheet for the exact product on your quote.
Do both go on the roof the same way?
Not always. Natural slate is normally nailed to battens, with each course overlapping the one below by a set amount. Manufactured slates may need special clips, specific nails or a certain batten spacing. This is the reason a swap is never just a matter of picking a different box of slates: the whole fixing method has to match what the maker specifies, and BS 5534 is the reference standard for how fixing should be done.
Whichever type is proposed, ask for the name of the quarry or the manufacturer in writing, so you know what you are agreeing to.
How long each one lasts
Lifespan is where natural slate has the clearest published figure. The CoRC advice page on roofing materials gives 100+ years for well-maintained slate. That is a typical figure for a good slate on a sound roof, not a promise. It also says something about maintenance: a slate roof stays sound only while someone keeps an eye on the fixings, the flashings and the gutters that sit around it, and a neglected roof of any material will fail early.
What usually fails on a slate roof?
On old roofs the slate itself is rarely the weak point. The iron nails corrode, the battens beneath soften and the slates start to slip, a condition roofers call nail sickness. A roof in that state can often be repaired by refixing the good slates and replacing the rest, which is why age alone does not mean the roof needs scrapping. Our page on nail sickness in slate roofs sets out how that is judged.
What about man-made slate?
This is the harder question, because manufactured slates are newer and each maker's product is different. Makers publish design lives and offer warranties, but a warranty describes what the maker will do if something goes wrong, and says little about how many winters the slates will stay sound. The nearest published comparisons concern tiles. Marley puts concrete tiles at around 60 years without offering that as a guarantee, and a Building Research Establishment minimum of 60 years applies to clay tiles only. Ask each maker for the evidence behind its claim and for the terms attached to its warranty.
Weight on the rafters and the approval question
Whatever sits on the battens is carried by the rafters, walls and foundations below, so the covering is a structural choice as well as a visual one. Slates differ in thickness and size, and manufactured slates differ from one another, so there is no single weight to give for either group. The useful comparison is between what is on your roof today and what is proposed.
Why does a change of covering need checking?
The Planning Portal sets two triggers for building control approval: a new material that makes the roof covering 15 per cent or more heavier, and one whose fire performance would differ significantly from the covering it replaces. Where weight is the issue, its advice is to involve a structural engineer or surveyor before any work starts. Approved Document A defines a significant change as loading rising by more than 15%. Swapping natural slate for natural slate usually stays far inside those limits. Moving from a lightweight covering to a heavy one is where trouble starts.
Does the size of the job matter?
Yes. The Planning Portal's usual test is that under 25 per cent of the building envelope and under 50 per cent of the roof is touched. In Crawley, the council's building control team lists repairing or replacing over 25% of the roof surface as approval work, and a whole slope on a modest house can pass that mark. Other council areas may word their rules differently, so ask your own building control body before work begins.
Your roofer should inspect the rafters and battens as soon as the first slates are off and report back before any new covering goes on. Ask for the weight per square metre of the exact product on your quote, taken from its data sheet, and compare it with the covering being removed.
Pitch, fixings and the look of the roof
Every covering has a minimum pitch, the shallowest slope on which it will shed water. Below it, rain can be pushed up under the slates in wind. The figure comes from the manufacturer and from the standard, and it is the first thing to check when a roof has a low or complicated pitch.
What is the minimum pitch for natural slate?
Cupa Pizarras, a Spanish slate producer, explains that BS 5534 sets 20 degrees as the shallowest pitch for natural slate. Its guidance also rules out hook fixings on any slope below 25°. A slate roof sitting at 20° therefore needs nailed fixings, not hooks. If you are replacing a lower roof, such as a dormer cheek or a porch, ask your roofer to confirm the pitch before the slate is ordered.
What about man-made slate?
Each maker sets its own minimum pitch for manufactured slates, and it may be higher or lower than natural slate's. There is no one figure to rely on, so read the data sheet for your product and ask the roofer to compare it with the measured pitch of your roof.
How do they look from the street?
Natural slate varies from slate to slate, and the surface changes with weathering. A manufactured slate is made in a mould or by a process that repeats, so the pattern may look more uniform, and some brands add a texture or colour variation to soften it. Neither is better or worse; it is a matter of the house and the street. Where a roof is part of a terrace or a group of matching houses, the odd man-made patch can stand out next to the weathered slate beside it, even if it matched when new.
Planning, conservation areas and old fibre-cement
Changing the covering on a house can alter how it looks from outside, and the rules treat appearance seriously in some places. This is general information, not advice, and your own council has the final say.
When should you ask the council first?
The Town and Country Planning Act 1990 leaves out of its definition of development any works that make no material difference to how a building looks from outside. Trading natural slate for a manufactured look-alike may change that look, so phone the planning team at your council before you commit. That matters most in a conservation area, inside a National Park or National Landscape, or where an Article 4 direction applies. A listed house needs its own listed building consent for changes that alter its character. The South Downs National Park Authority notes that ordinary maintenance and minor repairs done like for like need no such consent, which leaves a change of material outside that comfort zone.
Could an old roof contain asbestos?
For anything built or refurbished before 2000, HSE tells owners to treat asbestos as present until shown otherwise, and asbestos cement was a common material for roof sheeting. If your existing fibre-cement slates are old, do not drill, cut, scrape or pressure-wash them. Have a surveyor or a specialist identify the material before anyone works on the roof, because handling and disposal are tightly controlled. HSE adds that asbestos cement roofs are fragile, so nobody should step onto one.
Modern man-made slates sold new today are a separate matter, and the maker's data sheet will say what they are made of.
Typical prices and what to put in the quote
Slate roofs cost more than most coverings, and the gap comes from the material, the slower laying and the care needed at hips, valleys and abutments. Man-made products usually narrow that gap. Published national figures give a feel for the scale.
What do national guides say?
Checkatrade's roof repair guide, with its June 2026 table, gives typical UK repair rates per m² of £150 to £220 for Spanish natural slate and £90 to £130 for fibre cement, both before VAT and for small areas of up to 3 m². For a complete roof, HomeBuilding's guide, last updated 30 September 2025, puts a detached house with Welsh slate at £18,000 to £25,000. Use them to orient yourself only: scaffold, roof size and what lies under the old covering all push the total around, and VAT at 20% may be extra.
What should the written quote say?
Look for the product named in full, with the quarry or the maker, and the size and thickness of each slate. See that the quote says plainly whether VAT and scaffold are included. Then ask what happens if battens or rafters need work once the old covering is off, how the roof will be fixed and which pitch the product needs. If the quote says slate but gives no maker, ask which it is.
A survey of a slated roof with us ends with pictures of its condition and a single written total. To start sooner, send a picture of the ridge and one of the eaves, plus anything you know about where the slate came from. That gives us the first things to look at on that covering before we visit.
Part of our Pitched Roofing Services in Crawley
Slate roof queries
Can I mix man-made slates into a natural slate roof?
Roofers do it for repairs, but the two seldom weather alike, so the patch can stand out. Fixings and sizes may differ too. For a small fix, salvaged natural slate of the same size and tone is usually a closer match. Ask what is available before agreeing a repair.
Is Spanish slate as good as Welsh slate?
Both are natural slate, and quality varies by quarry rather than by country. The useful questions are the quarry's testing evidence, the thickness and the supplier's data sheet. Price differs between sources. Ask your roofer to name the exact product and the evidence behind it.
Does replacing slate with a lighter covering cut costs?
Not necessarily. A lighter product can allow lighter fixings, but the scaffold and the labour of stripping and relaying a covering remain, and a change of material may need council advice. Compare written totals for like with like, and check that each says whether VAT and scaffold are included.
