Clay roofing tile
| Clay roofing tile | |
| Standard | BS EN 1304:2013 |
|---|---|
| Material | Fired clay |
| Surface | Natural or engobe/glazed finish |
| Cleaning consideration | Surface finish is not renewable |
A clay roofing tile is a roof covering unit formed from fired clay. Product definitions and specifications for clay roofing tiles and fittings are given in BS EN 1304:2013.[1] Clay tiles are found on United Kingdom roofs in a wide range of ages, and their condition when a roof is cleaned depends far more on that age and on exposure than on the material itself.
Surface and weathering[edit]
Clay tiles may be left with a natural fired surface or finished with an engobe or glaze. That surface is formed in manufacture and cannot be restored on the roof: once it is worn or removed, what is exposed is the body of the tile beneath, which is more porous than the surface was.
This is the fact that governs cleaning. A more porous surface holds water for longer and gives growth a better hold, so a clean that removes surface material makes the roof more prone to regrowth than it was, not less. The effect is invisible on the day and appears over the following seasons.
Age and frost[edit]
Older clay tiles vary enormously in quality, and hand-made tiles from the nineteenth and early twentieth centuries are not comparable with modern extruded product. Water absorbed into a porous tile and then frozen is a well-recognised mechanism of failure, and a tile already spalling or delaminating at its edges is not a candidate for aggressive cleaning of any kind.
Assessment before work is therefore a question about this roof rather than about clay tiles in general.
Cleaning considerations[edit]
Because the surface is not renewable, methods that abrade it carry a permanent cost. Pressure sufficient to strip lichen from a fired clay surface will generally remove some of that surface. Chemical treatment leaves the surface untouched but works slowly, which is the trade-off in most clay roof cleaning decisions.
Walking a clay roof is its own question: individual tiles crack under point loading, and cracked tiles found after a clean are frequently attributed to the cleaning method when the cause was access.
See also
References
- ^BS EN 1304:2013: Clay roofing tiles and fittings. Product definitions and specifications. BSI. Retrieved 2026-09-05