What is a drip edge?
A drip edge (or weatherbar) is a projecting edge or profile at the bottom of a window frame, window, or window sill that directs rainwater away from the facade. Without a drip edge, water runs along the frame into the wall, causing moisture damage, algae growth, and rotting of the frame timber.
How does it work?
The drip edge protrudes a few centimetres from the facade. On the underside there is a drip groove (drip nose): a small channel that causes the water to detach and drip downward instead of running back along the wall.
The principle: water always follows the surface (capillary action). The drip groove breaks this — the water “drips off” at the lowest point.
Where are drip edges found?
- Under the window frame — The sill or a separate drip edge profile
- On the window sill — The external sill slopes downward and projects outward
- Above windows and doors — Sometimes a drip edge in the upper masonry
- On the fascia board — Drip edge at the top of the fascia board (on a flat roof)
Materials
| Material | Application |
|---|---|
| Aluminium profile | Under window frames, on fascia boards |
| Natural stone | Window sills |
| Concrete | Cast sills |
| Wood (profiled) | Part of a wooden window frame |
| Plastic | For plastic window frames |
Common mistakes
- No drip edge on the frame — Water enters the cavity or runs down the facade
- Drip edge mounted flat — Must always slope slightly outward (away from the building)
- No drip groove — Without a drip nose, water runs back along the wall
- Sealant over the drip edge — The sealant must not bridge the drip edge, otherwise it will not work
Related terms
- Window frame
- Plinth
- Fascia board
- Joint