Not which is better — that depends on the building. These are the actual material differences, and understanding them explains almost every price gap you will see.
Most comparisons of slate and tile are really arguments about which is better, and the honest answer to that is “it depends on the building”. This guide does something more useful: it sets out how the two genuinely differ as materials.
Understand those differences and almost every price gap, pitch restriction and structural caveat you will encounter makes sense on its own.
The single most consequential difference, and the one that explains the cost gap.
A large concrete interlocking tile covers a substantial area in one piece. A slate is much smaller. The result is that a slated roof takes several times as many units per square metre — and every one is lifted, positioned, aligned and nailed by hand.
So the difference between a slate roof and an interlocking tiled roof is a labour difference at least as much as a materials one. Natural slate is also the more expensive material, but on many roofs the labour gap is the larger part.
Slate is double-lapped: each course overlaps the two courses beneath, so there are always at least two thicknesses of slate over any point on the roof. That is what makes it weathertight, and it is why the piece count is so high.
Single-lap interlocking tiles overlap only the course below, and rely on a moulded interlocking edge at the sides to keep water out. Fewer pieces, less overlap, more coverage per unit.
Plain tiles sit in between: small units, double-lapped like slate, which is why they are the most expensive tile to lay by a wide margin.
| Natural slate | Plain tile | Interlocking tile | |
|---|---|---|---|
| Unit size | Small | Small | Large |
| Lap | Double | Double | Single, plus interlock |
| Units per m² | Many | Many | Few |
| Labour to lay | Slow | Slowest | Fastest |
Headlap is the amount by which each unit overlaps the one two courses below. It is not a preference — it is calculated from the pitch of the roof, the size of the unit and the exposure of the site.
The principle is straightforward: the lower the pitch, the greater the lap, because water moves more slowly down a shallow roof and wind can drive it further back up underneath. A more exposed site needs more lap independently of pitch.
The commercial consequence is that two roofs of identical area and pitch can need different numbers of units if their exposure differs — and that reducing the lap lowers the count and makes a quotation look cheaper. It is worth asking what headlap a quotation assumes.
Concrete tile is the heaviest common covering. Natural slate is one of the lightest, and fibre cement slate lighter still. Clay tile sits in between and varies by type.
This matters because a roof structure was framed for the weight of the covering it was built with. Going lighter is never a structural problem. Going heavier — typically slate to concrete tile on older property — is a question to answer rather than assume, and where the answer is unfavourable the fix is normally a lighter covering rather than strengthening the roof.
Every covering has a minimum pitch below which it is not warranted, because below that angle wind-driven rain gets pushed back up under the lap faster than the covering sheds it. It is not a formality — going below it voids the warranty for a good reason.
Slate tolerates the lowest pitches. Plain tiles need the steepest roofs. Interlocking tiles vary widely by range, and purpose-designed low-pitch tiles go considerably lower than the generic minimum.
In Frodsham this bites more than in some places, because the conservation area appraisal notes pitches that are not very steep. A roof that works in slate may sit below the minimum for the tile someone wants to put on it.
Slates are nailed individually, or hook-fixed, every one — there is no interlock, so each slate relies on its own fixings and on the courses above it.
Interlocking tiles are all mechanically fixed under the current British Standard. Plain tiles are fixed on a course pattern plus all perimeter tiles. In both cases the pattern comes from a calculation for the specific address rather than from habit.
The failure modes differ accordingly. A slate roof's classic weakness is nail corrosion over decades — every fixing the same age, failing together. A tiled roof's classic weaknesses are the ridge, hip and verge, because those were traditionally bedded in mortar, and mortar cracks.
Worth ending on, because it is the thing that actually decides how long a roof lasts.
Neither covering fails, in most cases. Roofs fail at the fixings, the battens, the underlay and the lead — all of which are the same job on a slate roof and a tiled one, and all of which are underneath the part you can see.
Two separate systems. Planning: a like-for-like re-roof does not materially affect the external appearance of a building, so under section 55 of the Town and Country Planning Act 1990 it is not development at all and needs no permission. A visible change of covering can be a different matter, particularly inside a conservation area, where the test is applied more tightly.
Building regulations: where more than 50% of the roof's surface area is renewed, or the work forms part of a major renovation, regulation 23 of the Building Regulations 2010 requires the roof to be brought up to current thermal standards so far as that is technically, functionally and economically feasible — 0.16 W/(m²K) for a roof in an existing dwelling. A patch repair does not trigger it, and neither does a roof over unheated space such as a detached garage.
We will tell you which coverings are genuinely available to your roof and what each would involve.
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