What is a fish-scale slate roof?
A fish-scale slate roof is a slate roof in which each slate has a rounded, semicircular bottom edge. Because the exposed tail of every slate is curved, the finished roof looks like the scales of a fish. In Dutch it is called a rensdak or schubbendak. The slates are often described as scalloped or fish-scale slates.
Characteristics
- Rounded slates: the visible lower edge of each slate is curved.
- Rising courses: in the Dutch and German tradition (Rijndekking, German slating) the slates are laid in diagonally rising lines rather than in the horizontal courses used with rectangular slates.
- Uniform or graduated sizes: in the German tradition, a roof of identical scale-shaped slates is a scale covering (Schuppendeckung). The Old German pattern (Altdeutsche Deckung) uses slates of different sizes, with the largest and thickest at the eaves and smaller ones towards the ridge, giving a lively roofscape.
Application
Smaller slates with a rounded tail follow curved surfaces better than wide rectangular slates. That is why fish-scale slating is common on spires, turrets, domes and curved roofs, and on churches and historic buildings. It is also used in decorative bands within an otherwise rectangular slate roof.
Practical tips
- Repair like for like. Patching a fish-scale roof with rectangular or fibre cement slates changes its appearance. On listed buildings this generally needs consent.
- Use a specialist slater. Graduated patterns in particular require slates to be sized and dressed on the roof.
- Don’t walk on the slates. Slate breaks under point loads. Use a roof ladder with a ridge hook or a proper walkway.
- Inspect regularly for slipped, cracked or missing slates and check the leadwork at abutments.
Related terms
- Slate roof
- Roof slate
- Slate
- Slate hook
- Diamond slate roof
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