How Do I Decide Between Slate and Tile for My New Roof?

This question usually gets answered with a comparison table, and there is one further down. But a table does not tell you what to do — it just lists differences.

What follows is a procedure. Take the questions in order and stop when you get a definite answer, because the later ones only matter if the earlier ones left the choice open.

Question 1: What Was the Building Originally Covered With?

The most reliable guide there is, and it costs nothing to establish. The roof structure was sized for the weight of the original covering, and the pitch was set for that covering's water-shedding characteristics.

How to find out

• Look along the street. On a group of similar houses the majority usually tells you. If most are slate and yours is not, yours was changed.
• Look in the loft. Old nail holes in the rafters at a closer gauge than the current battens indicate a previous covering of smaller units — which means slate.
• Look at the pitch. A roof at the shallow end for the tile on it was probably not designed for that tile.
• Look at the appraisal. Inside Neston's conservation area, the published appraisal records Welsh slate over local sandstone and brick.

→ If it was slate and it is still slate, put slate back. That is the technically straightforward answer, the visually correct one, and the one that raises no planning question. You can stop here.

If the covering has been changed at some point, or you want to change it, continue.

Question 2: What Is the Pitch?

This one rules options out, so it comes before preference.

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

→ If the roof is shallow, slate or a specific low-pitch interlocking tile may be the only options, and plain tiles are out. Measure before choosing — and measure any rear outrigger or later extension separately, because those frequently sit below the main slope.

Question 3: What Will the Structure Carry?

Concrete tile is the heaviest common covering; natural slate is one of the lightest; fibre cement slate is lighter still.

• Going lighter — tile to slate, for instance — is never a structural problem. The roof is being asked to do less.
• Going heavier — slate to concrete tile on older property — is a question to answer rather than assume.

→ If the structure is marginal, the answer is a lighter covering rather than strengthening the roof, in most cases. Modern lightweight interlocking tiles cover a lot of that ground, and fibre cement slate covers the rest.

Question 4: Is the Choice Yours?

A like-for-like renewal is not development at all and raises no planning question anywhere. A visible change of covering can be a different matter.

Inside Neston's conservation area the appraisal records Welsh slate over sandstone as characteristic, and a change away from that is assessed more tightly than a renewal would be. If the building is listed, listed building consent applies separately and does cover roof coverings.

→ One free call to Cheshire West and Chester Council settles this, and it should happen before quotations rather than after.

Question 5: Only Now, Preference and Budget

If you have reached this point, the constraints have not decided it and the choice is genuinely yours.

If budget is the constraint, there is one rule worth following: take the covering down a level before you take anything underneath it down a level. A good interlocking tile properly specified and fixed is a sound roof. A premium covering laid on re-used battens over old felt is not.

And the Thing None of This Decides

How long the roof lasts. Roofs almost never fail because the covering wore out — they fail at the fixings, the battens, the underlay and the lead, all of which are the same job whichever covering goes on top.

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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