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  • JRC Natural Slate Terminology

    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 laid.

    Head

    The upper edge of the width of the slate when laid.

    Angle of creep

    The angle of the spread of water beneath a butt joint.

    Pitch

    The angle of the roof slope.

    Margin

    The area of exposed slate when laid on the roof.

    Lap

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

    Bond or side lap

    The horizontal distance between the side of a slate and the side of the slate immediately above it. The bond should never be less than the lap.

    Gauge

    The vertical distance between the tail of one slate and the tail of the slate immediately above it. This can be calculated as follows:
    Gauge= length of slate – lap
    2

    Holing gauge

    The distance between the tail of the slate and the nail hole. This can be calculated as follows:
    Holing gauge= Gauge + lap + 15mm

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