Without the use of drip caps, when it rains water can run down in between the window sills and ledges and the walls of your home. This can lead to mold, rotting, staining and other damages. This damage can be easily prevented by the addition of window drip caps. They are very inexpensive and easy to install.
The first thing you need to do is measure all of the windows. Measure each window separately. Even if they are supposed to be the same size there could be a small difference. You will need to add some length to each drip cap. A few inches extra on each side should be enough.
You can buy preformed drip caps made from aluminum. There are also vinyl drip caps available. You can also purchase a sheet of aluminum and bend it and cut it with tin snips to make your own drip caps.
Check for Wood Rot
Gently pry up the layer of siding that is directly above the window. Examine the entire area. Look for any signs of rot, mold or decay. If there is none present you can continue to install the drip cap. If there are signs of decay you will need to fix this before continuing.
Remove as much rotten wood as possible. Use a chisel or screwdriver and remove the wood slightly beyond the end of the rotted wood. Let the wood dry out completely before proceeding.
Treat the wood with a chemical such as borate. Borates are derived from boron, which is a naturally occurring chemical that is non-toxic. It has been used to treat wood rot for a long time. When wet borates move through the wood they kill fungi and prevent future rotting.
Apply an epoxy resin. This will seep into the wood and harden it. It is dry when it no longer feels tacky. Use as much epoxy resin as necessary to fill in the place where the rotten wood was removed. After the epoxy has completely hardened, you can then sand the area to make it even. Finally, apply an acrylic primer and several coats of acrylic paint.
Even if there was no rot you should still clean the area thoroughly. Remove any organic material and wipe it down. Then let the area dry completely and proceed to the next step.
Cut the drip cap slightly longer than the window. Apply flashing tape to the area above the window. Then insert the drip cap up against the tape and under the siding. Center the cap above the window.
Secure the Drip Cap in Place
Next you will nail the drip cap in place. You should use galvanized nails. A galvanized nail has gone through a process which covers them with a zinc coating. This coating protects them from rust and corrosion.
Nail the drip cap in place. Make sure that the cap slopes away from the window. After the drip cap has been firmly secured, you will need to cover the exposed nails with roofing tar. You can use roofing felt instead of tar if you prefer. Apply caulk to the top edge of the drip cap.
Next you will need to cut both sides of the drip cap where the edges extend over the length of the window. Fold them in to prevent severe wind and rain from forcing water under the drip cap. Then you should apply caulk to both ends of the drip cap where they meet the house.
Apply an exterior grade sealant to the entire area where the drip cap meets the exterior of the house. Finally reattach the siding. Make sure the drip cap extends at least a quarter inch over the window to keep the rain from seeping up under the siding.
Photo by pasukaru76, Creative Commons Attribution License