|Basics of Concrete Roofing Elements (SKAT)|
A most important part
The importance of the supporting structure of a roof is often underestimated. Most damages to concrete roofing elements on roofs can be tracked down to faults in the roof structure and in the way the elements were placed and fixed.
Be aware of wind suction
In many cases the wind suction is higher than the wind pressure on the roof. If the roof structure is not designed to these strong uplift forces, heavy winds may destroy the whole root. This fact has to be considered in any kind of roof. be it covered with corrugated iron sheets, clay tiles or concrete elements.
The design of the roof for tiles and sheets should be simple The minimum pitch should be 22° in moderate climatic areas, whereas 30° are recommended for areas where torrential driving rains occur. The span of the rafters should not exceed 3,5 metres for lean-to roofs and 6 metres for gable roofs. For wider buildings, triangular trusses provide an economical solution up to a Limit of around 10 metres width.
Rigid timber structures
Good quality timber is desirable for the roof substructure though wood is getting scarce and expensive. Tiles and in particular pantiles are more adaptive to uneven substructures than semi-sheets and sheets. Pantiles may even be used on carefully selected poles. The timber consumption of a correctly dimensioned substructure is about equal for concrete tiles, semi-sheets or sheets as well as for a corrugated iron sheet roof. A clay tile roof normally requires more timber.
The installation of the substructure and the laying of the sheets should be done by a team of specialized carpenters and tilemakers. The tiles are fixed to the laths with special wire loops or fixing bolts.
Shape and size of the tiles may be adapted to the local needs