Concave and convex roof tiles are tiles with a curved shape: the concave tile lies with its concave side facing up and catches the water, while the convex tile lies over it with its convex side facing up and covers the joint. Together they form a watertight roof skin. The best-known example is the monk-and-nun system, in which a wide concave under-tile (nun) and a narrower convex cover-tile (monk) alternate.
How it works
The concave tiles form gutters that drain the rainwater to the eaves. The convex tiles lie over the adjoining edges of two concave tiles and so keep the joints closed. Because the tiles lie loosely over one another (sometimes bedded in mortar), the roof can breathe and the underlying timber stays dry.
Application
- Monks and nuns — historic and heritage roofs, monasteries and churches
- Curved tiles such as the pantile — modern variants with an undulating profile
- Restoration — when replacing, the concave and convex tiles must match each other and the batten gauge in size and profile
On a tiled roof, always pay attention to the correct batten gauge and to the closure of the tiles, so that driving rain cannot blow in.
Related terms
- Roof tile
- Concave tile
- Monk and nun
- Under-tile
- Cover-tile
- Batten gauge
- Roof covering
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