What is a drip edge?
A drip edge (also called a drip mould or drip groove) is a projecting profile, ledge or groove that prevents rainwater from running down a facade or other building element. The water — literally — drips off below the edge instead of wetting the underlying surface.
How does a drip edge work?
Water tends, through surface tension, to travel along a smooth surface. A drip edge interrupts this capillary action. Water collects on the underside of the moulding and falls off, rather than soiling or wetting the facade or wall.
The drip edge can take two forms:
- Projecting moulding — a physical, protruding ledge
- Drip groove — a routed groove or notch on the underside
Applications
Drip edges are found on:
- Window sills — to lead water away from window frames
- Cornices — at the top of a facade as the wall’s termination
- Window heads — to limit dirt staining below windows
- Balcony edges — to keep water away from the facade
- Chimney caps — on top of masonry chimneys
- Stringcourses and bandings — horizontal mouldings in brick facades
Materials
- Natural stone — granite, hardstone, often on representative facades
- Concrete — for concrete window sills and drip stones
- Zinc, lead or aluminium — as flashing or apron
- Plastic or aluminium profiles — on modern frames
- Wood — on timber frames, often with a routed drip groove
Detail
A good drip edge projects at least 30–50 mm from the facade and has a sharp edge or groove on its underside. A moulding without a drip groove will eventually lead to leaks and staining.
Related terms
- Sill
- Cornice
- Window head
- Drip
- Flashing
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