Two quotations can both say "natural slate" and be for materially different products at materially different prices. There is a published grading system that lets you tell them apart, and hardly anyone uses it.
Slate is the covering where quotations are hardest to compare, because "natural slate" is not a specification. It is a category containing products that differ enormously in quality, price and how long they will last — and the difference is not visible on a sample in a merchant's yard.
There is a published way to tell them apart. It is not widely explained to homeowners, and understanding it will do more for your decision than any price comparison.
BS EN 12326-1 is the standard covering slate for discontinuous roofing. It requires producers to declare how their slate performs in three tests, each expressed as a letter and a number. In every case, 1 is the best grade.
How much water the slate takes up by mass. There are two grades only.
How the slate behaves through repeated wetting and drying, which is really a test of how the metallic inclusions in the stone — pyrites and similar — oxidise over time.
How the slate stands up to atmospheric sulphur dioxide. This route applies to slate with a carbonate content at or below 20%; above that it is classed as carbonate slate and assessed differently, by the depth of the softened layer.
The grading is published by the producer in a declaration of performance — a manufacturer's document, not something the roofer writes. Your roofer obtains it from the supplier, and reputable slate producers publish them as downloadable PDFs on their product pages.
The document states the declared W, T and S classifications, the carbonate content, the thickness and the standard applied. The product will carry either a CE or a UK marking — CE marking continues to be recognised in Great Britain, so both are legitimate — and the marking references the declaration.
None of this is difficult to obtain. It is simply that almost nobody asks, which is why quotations get compared on the word "slate" and a total.
| Reputation | What actually matters | |
|---|---|---|
| Welsh slate | Premium; priced accordingly | Grading and thickness, as with any slate |
| Spanish slate | Enormous range, excellent to poor | The grading is the only reliable guide |
| Brazilian slate | Variable; some very consistent | Grading, and how it weathers in UK conditions |
| Reclaimed | Matches existing work | Unknown remaining life; every slate needs re-holing |
The country of origin is a weaker signal than the grading. A W1 T1 S1 slate from a good Spanish quarry is a better product than an ungraded slate from anywhere, and the price difference between grades within a single origin is often larger than the difference between origins.
Straightforward. Northwich has no Article 4 direction, so permitted development rights have not been withdrawn, and a like-for-like re-slate is not development at all under section 55 of the Town and Country Planning Act 1990 — it does not materially affect the external appearance of the building.
Northwich does have a town centre conservation area, which is on Historic England's Heritage at Risk Register — recorded in the 2025 register as in very bad condition but with a trend improving significantly, and containing 24 listed buildings. Inside it, a change of covering is worth raising with Cheshire West and Chester Council first; a like-for-like renewal is not. Listed buildings need listed building consent separately.
A re-slate renews a thermal element and engages regulation 23 of the Building Regulations 2010: thermal performance must be improved where technically and economically feasible, to 0.16 W/(m²K) for a roof in an existing dwelling under Approved Document L Volume 1. Sign-off is through council building control, a Registered Building Control Approver, or self-certification under a competent person scheme.
We will tell you which slate we are proposing, where it comes from and how it is graded. If you are comparing us with someone else, ask them the same question — the answer is a good deal more informative than the totals at the bottom of the page.
We will name the slate, its origin and its declared grading — not just the word "slate".
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They are the three declared performance gradings under BS EN 12326-1. W is water absorption, T is behaviour under thermal cycling — essentially how the slate's metallic inclusions oxidise — and S is resistance to sulphur dioxide. In each case 1 is the highest grade, so W1 T1 S1 is the best specification available.
Ask which slate it is, by producer and product name, and ask for the declaration of performance. That is a manufacturer's document; the roofer obtains it from the supplier. Reputable slate producers publish them as downloadable PDFs.
Welsh slate is generally regarded as the premium product and is priced accordingly, but "Spanish slate" covers an enormous quality range from excellent to poor. The grading tells you far more than the country does. A W1 T1 S1 Spanish slate is a better product than an ungraded one from anywhere.
T2 and T3 describe slate whose metallic inclusions oxidise. At T2 you get runs of rust discolouration down the roof without structural change. At T3 the oxidation penetrates the slate and can eventually produce holes.
Apex Roofing covers Cheshire and the surrounding area for complete roof replacement, new slate and tiled roofs and re-roofing.
Apex Roofing Cheshire · 105 Fence House, Fence Avenue, Macclesfield SK10 1LM
Tell us about the property and the roof in Northwich, and we will come back to you — usually the same day.
Prefer to talk? Call 07377 461095 · WhatsApp +44 7465 861265 · Email apexroofing14@gmail.com
