Slate vs Tile — Which Is Better for a New Roof in Wirral?

The usual way to compare slate and tile is cost, weight, lifespan and appearance. Those matter and they are covered below. But on the Wirral there is a fourth question that deserves to come first, because it is the one most likely to cause trouble: how does each behave in wind?

The Honest Answer on Wind

Neither covering is inherently better in exposure. What keeps a roof on is the fixing specification, and both slate and tile can be specified correctly or incorrectly.

What differs is how they are held down and where the weak points sit.

Tile

Held by nails, and on exposed sites by clips as well. Single-lap interlocking tiles are all mechanically fixed; plain tiles are fixed on a course pattern plus all perimeters. The classic weak points are the ridge, hip and verge, because those were traditionally bedded in mortar — and mortar cracks.

Slate

Held by nails or by hooks, individually, every one. There is no interlock, so a slate relies entirely on its own fixings and on the courses above it. The classic weak point is nail corrosion over decades rather than uplift on any given night.

Weight, and Why It Does Not Help

A common assumption is that a heavier covering resists wind better. It does not, to any useful degree — uplift acts on a large area and a correctly fixed light covering outperforms a poorly fixed heavy one comfortably.

Weight does matter, but as a structural question. Concrete tile is the heaviest common covering and natural slate one of the lightest. On the Wirral's older stock, much of which was framed for slate, going heavier is a question to answer rather than assume. Going lighter never is.

Pitch

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. Slate tolerates the lowest pitches; plain tiles need the steepest roofs; interlocking tiles vary widely by range.

This bites on rear outriggers and later extensions, which frequently sit below the main slope. It is a five-minute check at survey stage and it settles a great many arguments.

The Comparison

What Usually Decides It on the Wirral

• What the building was framed for. The structure was sized for the original covering and the pitch was set for its characteristics. Going back to it is nearly always the straightforward answer.
• The street. On a terrace or a pair of semis the roof reads as one plane, so a different covering on one half is visible from a long way off.
• Conservation area status. The borough has 26 conservation areas. A like-for-like renewal raises no question anywhere; a visible change of covering inside one does.
• Budget. And if that is the constraint, take the covering down a level before you take the fixings, battens, underlay or lead down a level.

The Regulations, in Brief

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.

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