Technical Terms

Face – The upper side of the slate when laid.

Bed – The underside of the slate when laid.

Tail – The lower edge of the width of the slate when fixed on the roof.

Head – The upper edge of the width of the slate when fixed on the roof.

Pitch – The angle of the roof slope between the ceiling joist and the rafter.

Margin – The area of exposed slate when laid on the roof.

Lap – The distance by which the tails of the slates in one course overlap the heads of the slates in the next course but one below.

Bond – The horizontal distance between the side of a slate and the side of the slate immediately above it.

Gauge – The vertical distance between the tail of one slate and the tail of the slate in the course immediately above it. This can be calculated by the formula: Gauge = (length of slate – lap) / 2

Holing Gauge – The distance between the tail of the slate and the nail hole. This can be calculated by the formula: Holing Gauge = Gauge + lap + 15mm