Minimum Headlap Pitch
Minimum Recommended Headlaps – Natural Roofing Slate
Headlap is the amount of overlap each roof slate has with the slates two courses below. The headlap is one of the most of important factors in making the roof watertight. In the Isle of Man, the minimum headlap is calculated using the SEVERE EXPOSURE table (56.5 l/m2 or greater per spell).
Minimum Rafter Pitch
20" x 10"(500mm x 250mm) Roofing Slate with 110mm headlap has a minimum rafter pitch of 27.5º.
20" x 12"(500mm x 300mm) Roofing Slate with 130mm headlap has a minimum rafter pitch of 22.5º.
When purchasing pre holed roofing slates with a 100mm headlap
20" x 10"(500mm x 250mm) Roofing Slate with 100mm headlap has a minimum rafter pitch of 30º.
20" x 12"(500mm x 300mm) Roofing Slate with 100mm headlap has a minimum rafter pitch of 30º.
It should be mentioned that under no circumstances should these slates be layed below 30º as this may result in water ingress. DON'T BE TEMPTED.
(Based on BS 5534: 2003 - All headlaps have been rounded up to the nearest 5mm increment)
Welsh Slate Limited click here
Minimum Recommended Headlaps – Natural Roofing Slate
Headlap is the amount of overlap each roof slate has with the slates two courses below. The headlap is one of the most of important factors in making the roof watertight. In the Isle of Man, the minimum headlap is calculated using the SEVERE EXPOSURE table (56.5 l/m2 or greater per spell).
Minimum Rafter Pitch
20" x 10"(500mm x 250mm) Roofing Slate with 110mm headlap has a minimum rafter pitch of 27.5º.
20" x 12"(500mm x 300mm) Roofing Slate with 130mm headlap has a minimum rafter pitch of 22.5º.
When purchasing pre holed roofing slates with a 100mm headlap
20" x 10"(500mm x 250mm) Roofing Slate with 100mm headlap has a minimum rafter pitch of 30º.
20" x 12"(500mm x 300mm) Roofing Slate with 100mm headlap has a minimum rafter pitch of 30º.
It should be mentioned that under no circumstances should these slates be layed below 30º as this may result in water ingress. DON'T BE TEMPTED.
(Based on BS 5534: 2003 - All headlaps have been rounded up to the nearest 5mm increment)
Welsh Slate Limited click here