Drip Cap (Rain Rail)

A drip cap, also known as a rain rail, is an exterior protective element integrated into the window frame design. While the seals between the window sash and frame already provide resistance against water and wind infiltration, the drip cap adds an extra layer of defense against the elements.

Mounted at the bottom of the window frame, the drip cap slightly overlaps the sash by a few millimeters. It is positioned just in front of the sash and frame, creating a barrier that shields the window from wind-driven rain. Water running down the exterior of the window is directed to flow between the drip cap and the sash/frame, preventing moisture from seeping into vulnerable areas.

This zone behind the drip cap is particularly sensitive to weather exposure, making the drip cap especially valuable in protecting against heavy rain, wind, and even hail.