Neston's conservation area appraisal records Welsh slate over sandstone. So on the older stock a tiled roof is usually a change of material — and that is a different question from a straight renewal.
The cost variables for a tiled re-roof are the familiar ones, and they are at the end of this guide. In Neston there is a question worth answering before them, and it depends entirely on which sort of property you have.
This is the straightforward case. A like-for-like tiled re-roof does not materially affect the external appearance of the building, so it is not development at all and no planning question arises — inside the conservation area as much as outside it.
What sets the cost is the same as anywhere: area and shape, the tile chosen, the condition of the timbers, access and the work that goes with it.
Then a tiled roof is a change of material, and Neston's conservation area appraisal is relevant. It records that the majority of the historic stock is eighteenth century and later, small in scale and vernacular, with Welsh slate roofs over local sandstone and brick.
That is a description of the area's character, and inside the boundary a visible change away from it is assessed a good deal more tightly than a renewal would be.
A roof framed for Welsh slate was sized for a lighter covering. Concrete tile weighs more per square metre than natural slate, and the increase is not trivial across a whole roof.
That does not mean it cannot be done. It means the rafters, purlins and wall plates should be looked at rather than assumed — and where they will not take a concrete tile, the answer is normally a lighter tile rather than strengthening the roof.
Slate performs at lower pitches than most tiles. A roof at the shallow end that works perfectly well in slate may sit below the minimum pitch for the tile you want. Every tile has a manufacturer's minimum, and going below it voids the warranty for a good reason: at too shallow an angle, wind-driven rain is pushed back up under the lap faster than the tile can shed it.
On small-scale vernacular property in a group, the roofs read together. A tiled roof in a run of slate ones is visible from a long way off, and on this stock that is worth weighing even where nothing formally requires a match.
| Concrete interlocking | Clay interlocking | Clay plain tile | |
|---|---|---|---|
| Material cost | Lowest | Higher | Highest |
| Units per m² | Fewest | Few | Many |
| Labour | Lowest | Low | Highest |
| Weight | Heaviest | Moderate | Moderate to heavy |
| Minimum pitch | Lowest | Low | High |
| Colour in 25 years | Weathers to grey | Holds | Holds |
| On vernacular property | Reads as modern | Better | Often best |
On small-scale older property the unit size matters more than most people expect. The eye reads a roof against the size of the units on it, so large interlocking tiles on a modest vernacular building make it look coarser and smaller. Plain tiles and slate are small-unit coverings, and a house designed around them tends to look wrong under large ones.
Ridge and verge. Older roofs have them bedded in mortar, which cracks over decades, admits water and eventually lets the tiles work loose. Mortar is still permitted as bedding but no longer counts as a means of fixing, so mechanical fixing is required either way — and on vernacular property it is worth asking which system, because they differ considerably in how conspicuous they are.
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 what your roof was built for and what it will sensibly carry.
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