Traditional slate names and sizes (mm) †
Empress (^650) ¾ 400 Wide Viscountess (^460) ¾ 255
Princess (^610) ¾ 355 Viscountess (^460) ¾ 230
Duchess (^610) ¾ 305 Wide Ladies (^405) ¾ 255
Small Duchess (^560) ¾ 305 Broad Ladies (^405) ¾ 230
Marchioness (^560) ¾ 280 Ladies (^405) ¾ 205
Wide Countess (^510) ¾ 305 Wide Headers (^355) ¾ 305
Countess (^510) ¾ 255 Headers (^355) ¾ 255
.. .. .. .. (^510) ¾ 230 Small Ladies (^355) ¾ 203
.. .. .. .. (^460) ¾ 305 Narrow Ladies (^355) ¾ 180
Sizes can also be cut to special order.
Generally, the larger the slate, the lower the roof may be pitched.
Also, the lower the roof pitch, the greater the head lap.
See also:
BS EN 12326-1: Slate and stone products for discontinuous
roofing and cladding. Product specification.
Slate producers' catalogues.
BS 5534: Code of practice for slating and tiling.
Slate quality Thickness (mm) Weight at 75 mm
headlap (kg/m^2 )
Best 4 26
Medium strong 5 Thereafter in propotion
Heavy 6 to thickness
Extra heavy 9Roof pitch (degrees) Min. head lap (mm)
20 115
25 85
35 75
45 65Roof Slating