How to Install Metal Flashing for Window Trimming

  • 2-8 hours
  • Beginner
  • 50-250
What You'll Need
Straight edge
Caulking gun
Metal flashing strips
Tape measure
Metal snips
Aluminum trim nails
Rag or cloth
Cleaning supplies

Metal flashing is a great addition to your home windows. This is an especially great installation if you have water coming in through your windows and need to prevent more from getting in. If you find yourself in this situation, here are a few tools and materials you will need, along with some quick steps to guide you through the process.

Step 1 - Measure

Measuring a few times for the metal flashing is the best idea. You need to make sure that you have everything right. You will want to measure both the inside and the outside, but make sure to take the larger number to work with. Keep in mind that this type of window has a 45 degree angle at the corners, so the in and out sides are going to be different sizes. It is much easier to cut for the longer size and make it smaller than it is to do it the other way around.

Step 2 - Cut

Use the metal snips to cut the metal flashing to the size of the window that you just measured out. Use the metal flashing piece that you just cut out and hold it up to the window to make sure that it fits properly. You may need someone to help you with this step so that you get everything fitting properly. Keep in mind that you want to take your time while measuring and fitting because flashing that doesn't fit won't work at all and it will just be a waste of your time to do it incorrectly.

Step 3 - Mark

Draw a line from the top of the top of the trim to the lower point where you clipped with a straight edge. This way you will be able to portray that angle on the top with the metal flashing as well.

Step 4 - Check and Clean

Once you are finished with that, you can check the side board and the sill. You want to be sure that everything is lining up properly. Use a rag or cloth and cleaning supplies to clean the area that you plan on attaching the metal flashing to. This is important because if your window is already damaged or dirty, it may just get worse from installing the flashing without cleaning it up. This dirt can end up getting hidden for a long time. Once everything has been spruced up, be sure that everything will be even and then attach the metal flashing. You again may want to have a partner help you with this step. Hold it up evenly and then use the aluminum nails with a hammer to put them up.

Be sure that you are consulting your village to make sure that you can install metal flashing on the window before you begin the actual project.