Tiles are lost in gales for one of two reasons: they were never fixed to the right specification, or the ridge and verge were relying on mortar. Both are avoidable.
A tiled re-roof on the Wirral is priced on the same things as anywhere — area and shape, the tile chosen, the state of the timbers, access — with one additional input that matters more here than inland.
Wind uplift. It decides how the roof is held down, and it is the difference between a roof that shrugs off a gale and one that loses units.
Three separate things do the work, and they fail in different ways.
Nails, and on exposed sites clips as well. Under BS 5534 the pattern is calculated for the address rather than chosen by habit, using distance from the sea, altitude, terrain, building height, roof pitch and the tested resistance of the specific tile.
| Covering | Minimum fixing requirement |
|---|---|
| Single-lap interlocking tiles | Every tile mechanically fixed, plus clips where the calculation requires |
| Double-lap plain tiles | Every fifth course twice-nailed, plus all perimeter tiles twice-fixed |
| All perimeter tiles | Two fixings minimum |
Perimeter tiles matter disproportionately, because uplift is highest at the edges and corners of a roof rather than in the middle. That is where a gale starts, and it is why the standard singles them out.
The traditional method was to bed them in mortar. Mortar is rigid, the roof moves, and over decades the bed cracks, admits water and lets the tiles work loose. On a hip that means they can slide.
Since the revision to BS 5534, mortar no longer counts as a means of fixing. Ridge and hip tiles must be mechanically fixed whether or not mortar is also used. In practice that usually means a dry ridge or dry hip system to BS 8612.
The edge of the roof at a gable, and another place uplift concentrates. Verge tiles are perimeter tiles and must be fixed at least twice.
Less than people expect. More nails, sometimes clips, a dry ridge and verge system instead of a bag of mortar, and the labour to fit them. It is a modest uplift on a whole-roof price.
Against that, set the cost of a scaffold, a call-out and a repair every time a gale takes a few tiles — and the fact that each of those visits pays for access, site set-up and disposal in full regardless of how small the repair is.
| Concrete interlocking | Clay interlocking | Plain tile | |
|---|---|---|---|
| Material cost | Lowest | Higher | Highest in clay |
| 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 in clay |
Two constraints sit above preference. Pitch: every tile has a manufacturer's minimum below which it is not warranted, because below that angle wind-driven rain gets pushed back up under the lap faster than the tile sheds it. Weight: concrete tile is the heaviest common covering, and on older property framed for slate that is a question to answer rather than assume.
There is also a headlap point specific to exposure. A more exposed roof needs a greater lap, which means more tiles per square metre for the same area. That is a real cost and it is also somewhere a quotation can be quietly trimmed.
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 the tile, the pitch, the headlap and the fixing specification for your address.
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