Drip groove
Drip groove refers to a carpentry or stonemasonry detail on the underside of plates, sections, blocks or mouldings. This is where a thin groove is cut into the length of an element between 5 and 20 mm away from the front edge on its underside, to help prevent water from running back on the underside and instead dripping down.
It is a detail that is commonly used on the underside of window and door cills to encourage water away from the timber to wall connection, discourage water ingress and reduce the risk of damage. It may also be a feature of stonemasonry such as coping stones to prevent water running down the surface of a wall, creating staining or damage. It may also be referred to as a kerf (groove or cut) because the width of the groove is often defined by the size of the blade used to cut it.
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