Last Updated: , Created: Friday, December 7th, 2001

Should I always use a drip cap over windows?

Bill from Paradise, Newfoundland writes: "I need to settle a bet between a buddy and myself. When you put in a vinyl window should a drip cap always be used? My buddy never uses one, and claims water never gets in under the window."

Well Bill, you win. Yes you should always put a flashing over the top of a window, called a Drip Cap. If you rely on caulking to prevent water from coming into this joint, it will eventually leak, sooner if the window sticks slight out beyond the siding as it usually does. Why? Because water will sit on that ledge and degrade the caulking. Critical joints like this one that could create a serious water leak must be flashed. That means that the flashing will shed the water, whether the caulking holds or not. We are relying on the overlapping to shed the water, just like we do with roof shingles. Caulking exposed to sunlight are used for minor joints, like along the side of the window, but anyplace where there is constant water flow, like over the top of the window, requires flashing.

Not only is it a good idea to use a drip cap -- it is code required. One important code detail often missed is that the drip cap, or headder cap flashing, must have a slope of a mininum of 6 degrees towards the outside.  Flat flashings collect water.   In fact in 2007 the Canadian code got even more strict and began to demand that the drip cap was made in a very special way with "end dams". For a full explanation, and even a video on how to do this, follow Header Flashing End Dams.


Keywords: Vinyl, Water, Flashings, Caulking, Joints, Siding, Codes, Windows, Leaking, Drip Cap

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