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

 

Roof Pitch

20

22.5

25

27.5

30

35

40

45 to 75

85+

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+

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

* Market 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.

 

 

 

 

 

Sales Office
Penrhyn Quarry
Bethesda
Bangor
Gwynedd
LL57 4YG

+44 (0) 1248 600656
enquiries@welshslate.com

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