How to Install a Window Trim Drip Cap

  • 2-4 hours
  • Intermediate
  • 500-750
What You'll Need
Galvanized Nails
Preformed Drip Cap (plastic or aluminum)
Exterior Sealant

Any window trim that has the potential to be exposed to moisture—either from inside or outside—has the potential to succumb to wood rot. A window trim drip cap can help avoid this costly problem by directing moisture away from the window from the top down. Preformed window trim drip caps are easy to find and install as a quick and easy project that will pay dividends in window maintenance costs down the road.

Step 1: Measuring Window

Since the window trim drip cap will serve as a sort of awning over the top of your window, the main measure that must be taken is the width of the window. While measuring, be sure to check to see whether wood rot is already present in your windows. If this is the case, the compromised wood will need to be replaced immediately. Once measurements have been taken, purchase preformed window trim drip caps from a home improvement center.

Step 2: Prepare Window and Begin Installation

Clear away any obstructions from the top of the window sill. Usually, this will mean removing the row of siding immediately above the window you are working on. Cut the drip cap you have purchased to a length slightly longer than the window you are protecting. Just about the window, apply flashing tape, then slide the drip cap against the flashing tape and under the siding above it.

Step 3: Secure Cap to Siding

Next, secure the drip cap to your siding using galvanized nails. Be sure that when you do this, the cap itself slopes away from the window downwards, forming an awning over the window. Apply caulk along the top edge of the drip cap. Using roofing tar or felt, cover the exposed nail heads.

Step 4: Cut Drip Cap To Secure Sides

In order to prevent rain from blowing in sideways and harming the window, you will need to create flaps out of the drip cap. To do this, cut lengthwise along the edges of the drip cap and fold the resulting piece in towards the window to create wind-resistant sides.

Step 5: Apply Finishing Touches

Finally, using any brand of sealant graded for external use, seal the top edge of each window trim drip cap in order to ensure that no water will be able to seep under the cap. Next, reattach siding. Caulk both sides of the drip cap. At this point, you are finished, and you should be left with a window that is secured against the elements and wood rot.