Roofing Slate Headlap
Slates fixed in accordance with the details given in this guide will have adequate resistance to wind loads, wind uplift and rain penetration under most conditions.
The tables below give minimum recommended laps according to exposure, roof pitch and slate size. Detailed guidance on wind load calculations is given in BS 5534 and BS EN 1991.
The recommendations for minimum pitches and laps for slate apply to normal situations. In general, the recommendations apply to rafter lengths of not more than 9m in moderate driving rain exposures and 6m in severe driving rain exposures.
Specifiers should take account of any abnormal condition that might apply and may need to specify greater values than the recommended minima. If it is necessary to use pitches lower than the recommended minima please contact Welsh Slate technical department.
Headlap Tables for Natural Slate BS5534
Once you have determined the degree of exposure of your site, use these tables to confirm the minimum headlap for your natural slate roof pitch, or see the range of roof pitches that would comply with the Standard, and which headlap minimum would be required for each.
Moderate Exposure Less Than 56.5l/m2/spell
|
|
Minimum Rafter Pitch |
20 |
22.5 |
25 |
27.5 |
30 |
35 |
40 |
45 to 75 |
85+ |
| Slate Size | ||||||||||
|
600x350 |
|
115 * |
105 * |
95 * |
85 * |
80 * |
70 * |
60 * |
55 * |
45 * |
|
600x300 |
|
190 * |
130 * |
95 * |
85 * |
80 * |
70 * |
60 * |
55 * |
45 * |
|
550x300 |
|
135 * |
105 * |
95 * |
85 * |
80 * |
70 * |
60 * |
55 * |
45 * |
|
500x300 |
|
115 * |
105 * |
95 * |
85 * |
80 * |
70 * |
60 * |
55 * |
45 * |
|
500x250 |
|
|
125 * |
95 * |
85 * |
80 * |
70 * |
60 * |
55 * |
45 * |
|
455x250 |
|
|
105 * |
95 * |
85 * |
80 * |
70 * |
60 * |
55 * |
45 * |
|
400x250 |
|
|
|
|
85 |
80 |
70 |
60 |
55 |
45 |
|
400x200 |
|
|
|
|
85 |
80 |
70 |
60 |
55 |
45 |
|
350x300 |
|
|
|
|
85 * |
80 * |
70 * |
60 * |
55 * |
45 * |
|
350x250 |
|
|
|
|
85 |
80 |
70 |
60 |
55 |
45 |
|
350x200 |
|
|
|
|
85 |
80 |
70 |
60 |
55 |
45 |
|
300x200 |
|
|
|
|
85 |
80 |
70 |
60 |
55 |
45 |
|
270x180 |
|
|
|
|
85 |
80 |
70 |
60 |
55 |
45 |
|
250x150 |
|
|
|
|
85 |
80 |
70 |
60 |
55 |
45 |
Severe Exposure 56.5l or greater/m2/spell
|
|
Roof Pitch |
20 |
22.5 |
25 |
27.5 |
30 |
35 |
40 |
45 to 75 |
85+ |
| Slate Size | ||||||||||
|
600x350 |
|
150 * |
130 * |
120 * |
110 * |
100 * |
85 * |
80 * |
70 * |
50 * |
|
600x300 |
|
|
165 * |
120 * |
110 * |
100 * |
85 * |
80 * |
70 * |
65 * |
|
550x300 |
|
180 * |
130 * |
120 * |
110 * |
100 * |
85 * |
80 * |
70 * |
50 * |
|
500x300 |
|
|
130 * |
120 * |
110 * |
100 * |
85 * |
80 * |
70 * |
50 * |
|
500x250 |
|
|
150 * |
125 * |
110 * |
100 * |
85 * |
80 * |
70 * |
70 * |
|
455x250 |
|
|
|
120 * |
110 * |
100 * |
85 * |
80 * |
70 * |
50 * |
|
400x250 |
|
|
|
|
|
100 |
85 |
80 |
70 |
50 |
|
400x200 |
|
|
|
|
|
100 |
85 |
80 |
80 |
80 |
|
350x300 |
|
|
|
|
|
100 * |
85 * |
80 * |
70 * |
50 * |
|
350x250 |
|
|
|
|
|
100 |
85 |
80 |
70 |
50 |
|
350x200 |
|
|
|
|
|
100 |
85 |
80 |
70 |
50 |
|
300x200 |
|
|
|
|
|
100 |
85 |
80 |
70 |
50 |
|
270x180 |
|
|
|
|
|
100 |
85 |
80 |
70 |
50 |
|
250x150 |
|
|
|
|
|
100 |
85 |
80 |
70 |
50 |
* Marked items may require longer or improved ring shank nails or increase slate thickness laps etc in areas likely to be exposed to very high winds. Project specific calculations can be carried out.
These tables give a range of sizes for your information.
Traditional sizes that are not listed above and random diminishing slates can be made to special order, please contact us for more information. BS 5534:2014 is the code of Practice for Slating and Tiling and describes the means of installing slates (nailing or hook fixings), plus the “headlaps” or “lap” required to ensure that the roof remains watertight, even at pitches as low as 20 degrees.
Download our Roofing Brochure for a Comprehensive Guide to Technical Requirements and Standards
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