How to Install Flashing on Windows with Vinyl Siding

Dormer windows
  • 6-40 hours
  • Intermediate
  • 0-300
What You'll Need
Window with vinyl siding around
Self-adhesive flashing strips
Felt or building paper
Tin snips
Pry bar
Old rags
Drip cap
Measuring tape
Exterior grade sealant

Protect your windows vinyl siding with flashing. Follow these simple steps to help the installation process go smoothly.

Step 1 - Prepare

Speak with someone in the building department in your town to make sure the flashing on the windows with vinyl siding is up to code.You will also want to try as best as you can to plan this project during a two to three day period where rain or snow is not expected as the caulk will need to set without getting wet. If this is not possible then attaching some sort of guard or tarp over while it is setting is also a possibility.

Step 2 - Materials

Since you are working with a vinyl siding around the window you will want to be using drip-cap flashing over the window or over a top trim that is installed. You will have to measure the width of the window to make sure you get the correct size drip cap.

Step 3 - Install the Drip Cap

Tan house with white trim around peak and windows

Using a pry bar you will need to remove a layer of siding from above the window you want to install the drip cap on. Use an old rag to remove any dirt or debris that may be there. Cut the drip cap to the correct size for your window. Attach the flashing tape above the window and then slip the drip cap into the siding and attach to the tape. Using a hammer, nail the cap into the siding. You want to make sure you are sloping the cap away from the window so that any water will run off. Then you can caulk all of the edges so water does not get in.

Use the tin snips to make two flaps on the edges so you can fold them in and keep the wind from blowing it. Apply the sealant and let it dry for 24 to 48 hours. Once you are finished you can re-attach the siding and caulk the edges, allowing that to dry for another 24 hours.

Step 4 - Install the Adhesive

Once you have the top finished with the drip cap you are able to get the sides. You can use self-adhesive flashing strips along both sides and the bottom. Before you attach them you will want to make sure the area is completely clean and dry so they stick as well as possible.

When you are done with this project you will want to try to allow the window to sit for a day or so without getting wet. If rain is expected, then place a tarp over to cover as much of the window and flashing as possible.