Plain and overlapping (mechanical) tiles
So-called ‘plain’ tiles are much smaller than canal tiles; they are rectangular and effectively flat, but have nibs underneath and are usually provided with nail holes so that they can be hooked over and nailed to timber battens. Traditional handmade plain clay tiles are still used throughout many parts of France.
Overlapping (or ‘mechanical’) tiles almost always have nibs underneath. They can be flat or ribbed and are manufactured to a profile such that they overlap or interlock with each other on their longer, inclined, edges and usually on their horizontal edges as well; this is intended to hold the tiles in place and to prevent rain from getting blown underneath them.
The main problems with plain or overlapping clay tiles are cracking and breaking, as a result of very high or very low temperatures. Another issue is ‘delamination’, which is where the surface gradually flakes away over the years – generally exacerbated by frost damage – until the tiles become porous.
It is usually possible to replace broken tiles on an individual basis but when delamination occurs it is often found to be widespread, particularly in the case of the thin interlocking type clay tiles that were used extensively about 60-70 years ago. So if this happens the entire roof covering might then need to be renewed.
A closer look
If you’re buying a house with a tiled roof I suggest you have the roof surfaces closely examined, ideally before making the purchase. It might be feasible to do this either yourself or with professional assistance from ground level, using binoculars, but if the roof has a low pitch and you can’t get far enough away to see it you might need to employ a contractor to get onto the roof using long ladders.
If it looks as though the roof is sagging, the structure itself may be at fault. Many older structures were not built to today’s standards and excessive deflection in the timbers can occur with age. This problem can arise if an old roof covering is renewed with heavier materials (slates being replaced with concrete tiles, for example); if you’re thinking of changing the roof covering with a different kind of material you should first have the structure itself checked.
It may well be possible to build in additional timbers to strengthen an otherwise weak or inadequate roof structure, but advice on this should be obtained from a properly qualified professional to ensure that alterations to the structure do not transfer the weight incorrectly.
A solid framework
Whereas pitched roofs have traditionally been built with a timber framework, there was a period some 40-50 years ago when steel trusses were incorporated, or the structure of pitched roofs was built wholly of steel members or concrete, particularly in areas of France where termites were a potential problem.
Flat roofs can be built wholly of timber, with a deck of timber boarding or, say, plywood panels over timber joists or beams, or steel or concrete beams can be incorporated. Alternatively the structure can be all concrete, perhaps using prefabricated sections that are simply dropped into place and covered with a thin cement screed.
A form of construction for flat roofs, terraces and internal floors, often found in French houses built 80-100 years ago, consists of steel beams typically spaced 500mm apart with vaulted/arched masonry of bricks or hollow clay blocks ( briques) in between, supporting a thickness of concrete above. It is unfortunate that in this kind of construction the concrete finish was mostly considered to be sufficiently dense, and it was not standard practice to provide a weatherproof finish. But over time, moisture can penetrate the concrete due to fine cracks or simply age. The problems I have commonly found are that the steel beams have corroded, and the brick arches in between have disintegrated. Obviously you need to be able to get underneath the structure to check for damage of this kind.
Sometimes it is feasible to provide a new weatherproof surface and simply clean up or reinstate the supporting structure, but other times the deterioration is so bad that I have to recommend complete or partial renewal of this kind of construction.
A similar situation frequently arises in the case of older flat roofs and terraces made of reinforced concrete where, due to a poor or non-existent weatherproof finish, moisture has penetrated the structure over the years such that the reinforcing steel inside has corroded and caused the relatively thin layer of concrete between the steel and the surface underneath to crack or even break away.
Older flat roofs that are not intended to be used as terraces may be covered with lead or zinc sheets. The best kind of surface for a flat roof is invariably asphalt, but it is expensive and normally found only on commercial buildings. Domestic flat roofs are usually covered with roofing felt or modern high-performance membranes that are made almost entirely of synthetic materials.
If a flat roof is to be used as an outdoor terrace it ought to be covered with tiles of some kind to protect the weatherproof surface underneath it. Flat roofs are not intended to be completely flat but should have a gradient (ideally not less than 1 in 60) sloping towards one or more rainwater outlets. Problems can arise where flat roofs have inadequate gradients. Unfortunately, it is usually a complicated and expensive job to improve the gradient of an existing flat roof.
If leaks occur in a flat roof you should check the condition of the ‘deck’ to which the roof covering is fixed before simply repairing or renewing the roof covering. Wood chipboard and certain other types of panels used for roof decks can be permanently damaged, and will not regain their original strength once they have become saturated.
Sad to say flat roofs in the drier parts of France are often constructed to a standard found to be lacking when a good downpour occurs so be warned!
All roofs that contain insulation should be adequately ventilated – something which is frequently overlooked when insulation is installed in a previously unventilated roof. Unventilated roofs can attract condensation, and this can have a harmful effect, particularly in roofs of timber construction.
Left: These mechanical (interlocking) tiles are probably getting on for 80 years old and will soon need to be renewed on a piecemeal basis or in their entirety
Right: The underside of a flat roof formed with vaulted brickwork between small section steel joists. Water penetration over the years has caused the components to deteriorate