Roof tiling and slating in Wisbech

The coverings, and how each behaves in wind

Clay pantile

The regional covering, and on the older buildings around the Brinks and the Market Place it is part of what the town looks like. A pantile is a single lap tile: it interlocks with its neighbour sideways and laps the course below, so a square metre of roof takes far fewer tiles than a plain tile roof does. Clay holds its colour indefinitely where concrete fades, and a sound pantile will outlast several sets of the fixings holding it down.

The exposure question is simple arithmetic. Fewer, larger units each covering more area means each one carries more wind load, and a nib-hung tile with no clip is held by weight and interlock alone, which on an exposed roof is not enough. Old hand made pantiles are also irregular, so they bed differently from modern machine made ones and mixing the two on a visible slope shows badly.

Concrete interlocking tile

Cheap per square metre, quick to lay and heavy, and the weight is genuinely useful in wind. Commonly quoted at 40 to 60 years. Its real weakness is the surface rather than the strength: the coloured coating weathers off, the concrete beneath is porous, and moss gets a grip on it. Colour fade is cosmetic. Delamination, where the surface flakes and the aggregate shows through, is the end of the tile.

Clay and concrete plain tile

Small format, double lapped and a far better looking roof than interlocking. Clay outlasts concrete comfortably and keeps its colour. The penalty is quantity: around six times as many tiles per square metre, so the labour line climbs sharply before the material does. In wind terms it is a very large number of small units each fixed to specification, which is robust when that specification is followed and quick to unravel when it is not.

Natural slate

The longest lived of the mainstream coverings. A well laid slate roof outlives the nails holding it, which is why the classic end of life is nail sickness rather than worn out slate. Not all slate is equal: Welsh slate and good imported Spanish slate are different products at different prices, and cheap imported slate with a high pyrite content can rust and split within a couple of decades, so ask for the source and the grade in writing rather than accepting the word slate.

On an exposed roof the head lap matters as much as the slate itself. Too little lap and driving rain gets past it regardless of how good the material is.

Reconstituted and fibre cement slate

Manufactured to look like slate for considerably less money, and lighter and easier to lay than the real thing, so uplift resistance rests entirely on the fixing. Read the guarantee properly, because its length and what it actually covers are two different questions. In a conservation area or on a listed building these are usually not acceptable, so check before the price makes your mind up for you.

The fixing specification is the argument that matters here

If you take one thing from this page, take this. On flat, open ground the difference between a roof that lasts and a roof that starts shedding tiles in its second decade is very rarely the tile. It is how the tiles, and particularly the ones at the edges, are held down.

Traditionally ridge, hip and verge tiles were bedded in sand and cement. Mortar is a bedding, not a fixing. It cracks with frost and thermal movement, and once a ridge or verge tile is loose at one end the wind has something to pull on. The current British Standard for slating and tiling reflects that: ridge and hip tiles are expected to be mechanically fixed rather than held by mortar alone, and the fixing schedule for the roof as a whole is meant to be calculated from wind loading, site exposure and the geometry of the building rather than carried over from the last job.

That calculation is what makes an exposed fen site different on paper as well as in practice. Uplift on the perimeter and corner zones is markedly higher than in the middle of a slope, so a properly specified roof is fixed more heavily at the verges, eaves and ridge, and on a very exposed roof every tile may need clipping rather than every second or third one. It costs more on the day and it is the most effective thing you can spend the money on here.

Dry fix

The industry's answer is dry fix. A dry ridge system clamps or screws each ridge tile onto a ventilated roll rather than sticking it down, and dry verge units clip over the gable end tiles. No mortar to crack, no repointing in fifteen years, and the roll ventilates the roof space.

• Ask whether the quote uses mortar or dry fix, because it is a genuine price difference and a genuine performance difference
• Mechanical fixing at ridge and hip is not optional under the current standard, whatever a quote implies
• Ask what the tile fixing schedule is, and whether perimeter and corner zones are treated differently from the middle of the slope
• A dry ridge roll ventilates at the ridge as well, which helps a cold roof space considerably

One caution, and it is a real one in this town. Plastic dry verge units clipped along the gable of a Georgian house look exactly like what they are, and on a listed building or in a conservation area they will usually not be accepted. The right answer there is mortar bedding with proper mechanical fixing behind it, which gets the performance without the appearance. A firm offering only one of those options has not thought about your building, and how to choose a roofer covers how to tell in a conversation.