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Roof Slate Chart
Moderate Exposure (less than 56.5 l/m2 per spell)

Pitch Slate Length Slate Width Min Headlap Slates Batten Guage Hole Guage Ave Weight
deg. mm mm mm no./m2 mm mm kg/m2
45 508 280 54 15.73 227 291 27.7
45 508 254 54 17.34 227 291 27.7
45 457 254 54 19.54 202 266 28.1
45 406 254 54 22.37 176 240 28.6
45 406 203 54 27.99 176 240 28.6
40 508 280 60 15.94 224 294 28.1
40 508 254 60 17.58 224 294 28.1
40 457 254 60 19.83 199 269 28.5
40 406 254 60 22.76 173 243 28.6
40 406 203 60 28.47 173 243 28.6
35 508 280 67 16.20 221 298 28.6
35 508 254 67 17.85 221 298 28.6
35 457 254 67 20.19 195 272 29.1
35 406 254 67 23.23 170 247 29.7
35 406 203 67 29.06 170 247 29.7
30 508 280 77 16.57 216 303 29.2
30 508 254 77 18.27 216 303 29.2
30 457 254 77 20.72 190 277 29.8
30 406 254 77 23.93 165 252 30.6
30 406 203 77 29.95 165 252 30.6
27.5 508 280 83 16.81 213 306 29.6
27.5 508 254 83 18.53 213 306 29.6
27.5 457 254 83 21.05 187 280 30.3
25 508 280 91 17.13 209 310 30.2
25 508 254 91 18.88 209 310 30.2
25 457 254 91 21.51 183 284 31.0
22.5 508 280 101 17.55 204 315 30.9
22.5 508 254 101 22.12 178 289 31.8
20 508 254 125 20.56 192 327 34.7
20 457 254 125 23.72 166 301 36.0
20 457 220 130 27.80 164 304 36.6

The above recommendations apply to rafter lengths of not more than 9m.		 Severe Exposure (equal to or more than 56.5 l/m2 per spell)

Pitch Slate Length Slate Width Min Headlap Slates Batten Guage Hole Guage Ave Weight
deg. mm mm mm no./m2 mm mm kg/m2
45 508 280 69 16.27 220 299 28.7
45 508 254 69 17.94 220 299 28.7
45 457 254 69 20.29 194 273 29.2
45 406 254 69 23.37 169 248 29.9
45 406 203 69 29.24 169 248 29.9
40 508 280 76 16.53 216 302 29.2
40 508 254 76 18.23 216 302 29.2
40 457 254 76 20.67 191 277 29.7
40 406 254 76 23.86 165 251 30.5
40 406 203 76 29.86 165 251 30.5
35 508 280 86 16.93 211 307 29.8
35 508 254 86 18.66 211 307 29.8
35 457 254 86 21.22 186 282 30.5
35 406 254 86 24.61 160 256 31.5
35 406 203 86 30.79 160 256 31.5
30 508 280 98 17.42 205 313 30.7
30 508 254 98 19.20 205 313 30.7
30 457 254 98 21.93 180 288 31.6
30 406 254 98 25.56 154 262 32.7
30 406 203 98 31.99 154 622 32.7
27.5 508 280 106 17.77 201 317 31.3
27.5 508 254 106 22.43 176 292 32.3
25 508 280 116 18.22 196 322 32.1
25 508 254 116 23.09 171 297 33.2
22.5 508 280 128 18.80 190 328 33.1

The above recommendations apply to rafter lengths of not more than 6m.
It should be noted that, whilst the above figures apply in general terms for most modern slates, these charts do not apply to heavier types such as Burlington slates.
In addition, any abnormal conditions that might apply should also be taken into account.
Burlington Roofing Design Guide (pdf)
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