Wood Shingle and Stone Slab Roofing

The honest answer is that it depends on three things, and none of them is the quality of the shingle. The first is exposure: a north-facing slope, which dries slowly and stays damp, has a noticeably shorter life than a south-facing one, on the same roof and in the same material, and it is normal to find historic roofs where the two slopes were renewed at different times. The second is ventilation: a covering that dries from both faces lasts far longer than one laid on a closed substrate, and this is the difference the designer can actually govern. The third is the timber species and how the shingle was produced, because a shingle split along the grain behaves much better than a sawn one, where the cut severs the fibres and opens a path for water. Put these conditions together and you commonly speak of decades, with maintenance replacing individual elements along the way. But a well-made covering on the wrong roof will not reach half that time.

Generally no, and the reason is worth understanding because it applies to all exposed timber. Any film-forming treatment, meaning one that leaves a surface skin, makes things worse rather than better on a discontinuous covering: the film slows evaporation without really stopping water entering at the edges and joints, so moisture stays inside the element longer. The film also ages and flakes unevenly, and renewing it would mean treating a whole roof element by element, which nobody ever does. The correct strategy is the opposite and simpler: choose a naturally durable species, guarantee ventilation on both faces, and accept that the covering will go grey. That grey is not decay, it is the surface layer oxidised by ultraviolet light, and it is the natural protection of the timber beneath. If the client does not want the grey, the problem is not the treatment: it is that they probably do not want a timber roof.

No, and the reason is almost always structural before it is technical. Stone weighs many times more than a clay covering and still more than a metal one, so the first step is not choosing the stone but verifying that the structure can carry it, including the snow load, which in the places where stone slabs are traditional is never negligible. In refurbishment there is a further fact often taken for granted: that the roof originally had stone slabs does not prove it can carry them today, because the structure has worked for decades, the beam ends at their bearings are the most degraded point, and the sizes of that time were not calculated as we calculate now. Then there is a geometric condition: stone slabs need generous pitches, because their head lap cannot grow indefinitely and their irregular surface slows the run-off. On a flat roof plane a stone covering does not behave as it should, and no laying technique recovers the pitch that is missing.

Very little, but not none, and the difference between the two is the entire service life of the roof. The useful inspection is annual, preferably after winter, and consists of three simple things. Look at the covering from outside for split, slipped or missing elements, which should be replaced individually and at once, because while they are few the repair is trivial. Clear gutters and valleys of leaves and needles, which accumulate on these roofs more than elsewhere because of the irregular surface. And above all go up into the roof space with a torch on a sunny day and look upwards: points of daylight visible from inside and dark stains on the structure tell you in minutes what cannot be seen from outside. The client should also be left a stock of elements from the same batch, because years later they can no longer be matched for colour and format, and a repair made with different material shows forever.