When you price a new natural slate roof the first question is usually where the slate comes from. Welsh slate sits at the top of the price list, Spanish slate is the common middle-market choice, and Brazilian slate turns up as a cheaper alternative on quotes that do not say much about it. The three are all real stone and all keep rain out, but they are not interchangeable. They differ in how they are formed, how they split, how they age, what they cost and how much you can learn about a particular batch before you buy. This guide compares them on the points that matter on a real roof.
Where the slate comes from and why it matters
Slate is formed from clay and mud compressed and heated deep in the earth over a very long time. The conditions differ from one deposit to the next, and so does the stone. The resulting rock splits along its grain into thin sheets, and its quality depends on how fine the grain is, how little water it takes in, how free it is of minerals that react with air and rain, and how evenly it splits.
Welsh slate comes mainly from the quarries of north Wales, where the rock is some of the oldest and densest worked for roofing in Britain. It has been used on British roofs for hundreds of years, and it is the slate on many of the Victorian and Edwardian houses around Basingstoke, which arrived by rail. Spanish slate comes mostly from the north-west of Spain, in Galicia and neighbouring regions, where large modern quarries supply much of the European roofing market. Brazilian slate is quarried in the state of Minas Gerais and exported in large volumes to the UK and elsewhere.
Welsh slate
Welsh slate has the longest record on British roofs. Its stone is fine-grained and dense, takes in very little water, and resists frost, which is why Welsh-roofed houses are still shedding rain after a century and a half. The colours range from blue-grey through purple to green, and the surface is smooth with a slight sheen. Most Welsh slate keeps its colour well, though some varieties develop a gentle weathering over time.
The strengths are durability, a proven record, and an appearance that suits period houses. If you are repairing an existing Welsh slate roof, Welsh stock is the natural match. It is also the choice that conservation officers expect on many listed buildings, as the page on listed and period slate roofing explains.
The drawbacks are price and availability. A published guide puts installed Welsh slate at £140 to £180 per m², the top of the natural slate range. Some sizes and grades are in short supply, and lead times can be long. A very small number of quarries means little choice.
Spanish slate
Spanish slate is a large part of the UK market because it offers real stone at a lower price. Good Spanish slate is dense, hard-wearing and tests well, and many roofs laid with it in recent decades are performing as expected. The colour is usually a uniform grey or blue-grey, and the surface is flat and even, which suits modern houses and new-build estates. The slate is cut to consistent sizes, so laying is straightforward.
The same guide quotes Spanish installed at between £100 and £130 for each square metre. That price difference is the main reason it is chosen. It is also why the quality is the issue to watch: Spanish slate is quarried from many sources with different qualities. Some is excellent. Some has a higher water absorption, or contains minerals that cause staining or weathering. The stone you buy depends on the quarry, the grade and the supplier, so the origin alone does not tell you the quality. A reputable supplier will provide test data to the European standard for roofing slate, and your roofer should ask for it.
Brazilian slate
Brazilian slate is generally the cheapest of the three on the pallet, and it is frequently used where the budget is tight. It can be a good product, with attractive colours that range from silver-grey to black. Some Brazilian stone, however, has a reputation for rust staining and for variable thickness, and the quality across suppliers is more uneven than with the other two. As with Spanish slate, a batch that comes with test certificates is a different proposition from one that does not.
We would not rule out Brazilian slate, but we would want to see the specification and the test data before using it on a house, and we would be wary of any quote that says only imported slate with no origin or grade. For a listed building or a conservation area, a council would normally want a closer match to the original, which for most of Hampshire and Berkshire means Welsh.
Side by side
| Point | Welsh | Spanish | Brazilian |
|---|---|---|---|
| Installed price (typical UK range) | £140 to £180 per m² | £100 to £130 per m² | Usually below Spanish; no reliable range found |
| Appearance | Blue-grey to purple, slight sheen | Even grey or blue-grey, flat face | Silver-grey to black, varies by batch |
| Track record on UK roofs | Longest | Good where the grade is good | More mixed |
| Availability | Limited sizes, longer waits | Wide choice, ready stock | Wide choice |
| Best suited to | Period homes, matching repairs, listed buildings | Modern homes, extensions, good-value re-roofs | Budget jobs with test data |
How to judge any slate before you buy
Whichever origin you choose, a few checks apply.
- Ask for the test data. The European standard for roofing slate covers water absorption, resistance to thermal cycling, and the effect of acid and weather on the stone. A supplier should provide the results for the batch.
- Look at a sample. Check the thickness, the edges, the flatness and the surface. Tap it for a clear ring.
- Ask for the grade. Slate is sold in grades, and the lower grades have more flaws.
- Ask about the guarantee. A supplier's guarantee covers the stone and is separate from the roofer's guarantee on workmanship.
- Look at local roofs. A roof laid with the same slate five or ten years ago shows how it ages.
Fixing and laying matter as much as origin. Even the best slate fails early on poor nails, and a good roofer will use copper or stainless steel. The hooks-versus-nails comparison goes into the options.
Sizes, thickness and the look of the courses
Slate is sold in standard lengths and widths, and the size changes how the roof looks as well as how it performs. Longer slates give a bigger head lap, which is the overlap that protects the joints from driven rain, and are the better choice on low pitches or exposed sites. Shorter, smaller slates suit small roofs and give a finer, more traditional appearance. Welsh quarries have traditionally cut a wide range of sizes, including the old named sizes, while Spanish and Brazilian suppliers focus on a smaller set of common sizes that sell in volume. If your roof needs an unusual size to match what is there, you may be steered towards Welsh or reclaimed stock simply because nothing else will fit.
Thickness varies as well. Thicker slate is heavier, stronger underfoot and slower to lay; thinner slate is lighter and cheaper to carry. The best-regarded slate is thin, flat and strong, which is a property of the stone and not of the label. Check the weight per square metre in the specification against what the rafters can carry, because a covering heavier by 15% or more than the old roof needs approval. Our page on how heavy a slate roof is sets out the numbers.
How each slate ages on the roof
Good slate hardly changes. The surface dulls a little, lichen may settle on the shaded side, and the colour softens. That is normal and does no harm. The problems come from stone that is not good. Slate containing iron minerals can show orange or brown rust streaks, and slate with carbonate in it can weather to a chalky, pitted surface as rain slowly dissolves it. Poor-quality slate can also split into layers, which is the failure we discuss in the page on why slates delaminate.
These faults take years to show, which is why a cheap imported slate can look fine for the first ten winters and then begin to fail. It is the reason to buy on test data and track record, not on appearance alone. Roofs of Welsh slate more than a century old are common; a roof of newer imported slate has a shorter history to point to, even where the early signs are good.
Cost in context
Labour makes up around half to three-fifths of a slate roof's cost according to one published guide, so the difference between Welsh and Spanish on the pallet is only part of the difference on the invoice. For a roof of 60 m², the quoted ranges work out at about £8,400 to £10,800 for Welsh and £6,000 to £7,800 for Spanish, before scaffold, timber, lead and extras; that is an illustration from the sourced ranges, not a quote. Our page on what a slate roof costs sets out how the rest of the price builds up, and the final figure follows the survey.
The gap of a couple of thousand pounds over a roof's life is small if the Welsh stone lasts significantly longer, and large if it does not matter to you. That is why the answer depends on the house. On a Victorian terrace where the neighbours' roofs are Welsh, matching has real value. On a 1990s semi with concrete tiles that you are replacing with slate for the look, Spanish is a sensible compromise.
Our recommendation approach
We do not push one origin. The survey notes the existing covering, the age and style of the house, whether it stands in a conservation area, and what your budget allows. The report sets out two options where there is a real choice, with the slate named by origin, size and grade, and the fixings named too. If your roof has years left, we say that, and if reclaimed slate is a better match, we say so; see our guide to reclaimed slate.
The price is fixed in writing, the work carries a ten-year guarantee on workmanship, and the site is left clear. For the full service see slate roofing in Basingstoke, or arrange a visit by ringing 01256 213956 or messaging us on WhatsApp.
