The UK has been supplied with its own slate resources from
quarries in Wales, Cornwall and Westermorland. Imported slate is
also available from Spain, Argentina and parts of the Far East.e.g. Countess slate, 510¾255 mm laid to a 30° pitch with 75 mm
head lap.Batten gauge = (slate length † lap)... 2
= (510 † 75)...2 = 218 mm.Holing gauge = batten gauge+head lap+8 to 15 mm,= 218+ (^75) +(8 to 15 mm) = 301 to 308 mm.
Side lap = 255...2 = 127 mm.
Margin = batten gauge of 218 mm.
Eaves course length = head lap+margin = 293 mm.
Roof Slating