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Slate Manual – Page 10

Slate Laps, Sizes and Covering Capacities

Slate Laps for Varying Pitches

 

Minimum recommended lap for different roof pitches in mm
Normal Exposure Severe Exposure
Type Slate Size Minimum Roof Pitch Minimum Roof Pitch
mm in. 20° 22½° 25° 30° 35° 40° 45° 85° 22½° 25° 30° 35° 40° 45° 85°
Princess 610 x 355 24 x 14 115 105 90 75 75 65 65 * 125 105 90 75 75 65 *
Duchess 610 x 305 24 x 12 * 115 90 75 75 65 65 * * * 110 90 80 70 *
Small Duchess 560 x 305 22 x 12 115 105 75 75 75 65 65 * 120 105 90 75 75 65 *
Marchioness 560 x 280 22 x 11 * 110 90 75 75 65 65 * * 110 105 85 75 65 *
Wide Countess 510 x 305 20 x 12 115 105 90 75 75 75 65 * * 100 85 75 75 65 *
Countess 510 x 255 20 x 10 * 110 90 75 75 75 65 50 * 115 100 90 75 65 65
460 x 305 18 x 12 115 105 90 75 75 65 65 50 * 110 85 75 75 65 65
Wide Viscountess 460 x 255 18 x 10 * 110 90 75 75 65 65 50 * 115 100 85 75 65 65
Viscountess 460 x 230 18 x 9 * * 100 75 75 65 65 50 * * * 105 85 65 65
405 x 305 16 x 12 * * * 75 75 65 65 50 * * 90 80 75 65 65
Wide Ladies 405 x 255 16 x 10 * * * 75 75 65 65 50 * * 100 95 75 65 65
Broad Ladies 405 x 230 16 x 9 * * * 75 75 65 65 50 * * 100 100 85 65 65
Ladies 405 x 205 16 x 8 * * * 75 75 65 65 50 * * 105 100 90 65 65
Headers 355 x 255 14 x 10 * * * 75 75 65 65 50 * * 80 75 75 65 65
Small Ladies 355 x 205 14 x 8 * * * 75 75 65 65 50 * * 90 85 75 65 65
Narrow Ladies 355 x 180 14 x 7 * * * 75 75 65 65 50 * * 95 90 80 65 65
Slate Sizes and Covering Capacities

 

50mm Lap 75mm Lap 100mm Lap
Type Slate Size No of Slates per m² Battening Gauge in mm Batten Length per m² in mm Eave Slate Length in mm Holing Gauge in mm No of Slates per m² Battening Gauge in mm Batten Length per m² in mm Eave Slate Length in mm Holing Gauge in mm No of Slates per m² Battening Gauge in mm Batten Length per m² in mm Eave Slate Length in mm Holing Gauge in mm
mm in.
Princess 610×355 24×14 10.06 280 3.57 330 345 10.55 267 3.75 342 357 11.05 255 3.92 355 370
Duchess 610×305 24×12 11.71 280 3.57 330 345 12.28 267 3.75 342 357 12.86 255 3.92 355 370
Small Duchess 560×305 22×12 12.86 255 3.92 305 320 13.55 242 4.13 327 342 14.26 230 4.35 330 345
Marchioness 560×280 22×11 14.01 255 3.92 305 320 14.76 242 4.13 327 342 15.53 230 4.35 330 345
Wide Countess 510×305 20×12 14.26 230 4.35 280 295 15.11 217 4.61 292 307 15.99 205 4.80 305 320
Countess 510×255 20×10 17.05 230 4.35 280 295 18.07 217 4.61 292 307 19.13 205 4.80 305 320
460×305 18×12 15.99 205 4.88 255 270 17.08 192 5.21 267 282 18.21 180 5.56 280 295
Wide Viscountess 460×255 18×10 19.13 205 4.88 255 270 20.42 192 5.21 267 282 21.78 180 5.56 280 295
Viscountess 460×230 18×9 21.21 205 4.88 255 270 22.64 192 5.21 267 282 24.15 180 5.56 280 295
405×305 16×12 18.52 177 5.65 227 242 19.87 165 6.06 240 255 21.57 152 6.58 252 267
Wide Ladies 405×255 16×10 22.16 177 5.65 227 242 23.77 165 6.06 240 255 25.80 152 6.58 252 267
Broad Ladies 405×230 16×9 24.56 177 5.65 227 242 26.35 165 6.06 240 255 28.60 152 6.58 252 267
Ladies 405×205 16×8 27.56 177 5.65 227 242 29.56 165 6.06 240 255 32.09 152 6.58 252 267
Headers 355×255 14×10 25.8 152 6.58 202 217 28.01 140 7.14 215 230 30.88 127 7.87 227 242
Small Ladies 355×205 14×8 32.09 152 6.58 202 217 34.84 140 7.14 215 230 38.41 127 7.87 227 242
Narrow Ladies 355×180 14×7 36.55 152 6.58 202 217 39.68 140 7.14 215 230 43.74 127 7.87 227 242