What is drip edge for windows, and do you need it?
Short answer. Window drip edge, usually called a drip cap or head flashing, is a small metal or vinyl profile installed over the top of a window or door trim so water running down the wall is kicked out past the trim instead of soaking in behind it. It matters most on windows without a protective overhang, especially with wood trim.
How it works
Rain running down siding hits the flat top of window or door trim and can sit there or wick behind it. A drip cap covers that top edge, slopes outward and ends in a small lip that throws water clear of the trim. Behind it, the cap tucks up under the siding and the house wrap so water cannot get behind the cap itself.
How it is installed correctly
- The window is flashed into the wall with flashing tape, with the head flashing applied last.
- The drip cap sits on top of the head trim, extending slightly past each side.
- The house wrap above lays down over the cap's vertical flange, like shingles, never tucked behind it.
- Siding goes on over the cap with a small gap so water drains off.
Signs yours is missing or failing
- Peeling paint or soft wood along the top of the window trim.
- Water stains on the interior wall above or beside the window.
- Caulk being used as the only seal at the top of the trim.
When the roof is the real culprit
Where a roof meets a wall just above a window, water can run off the roof edge and down the wall behind the siding. A missing kickout flashing at the bottom of that roof-to-wall joint is a common cause of rot around windows below it. More in roof flashing explained and common causes of roof leaks.