Things You'll Need:
- Prebent metal flashing strips
- Tool to measure
- Pencil
- Metal snips
- Straight edge
- Cleaning rags and materials
- Aluminum trim nails
- Caulk
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Step 1
Use the aluminum strips that you already bent for the window trim. Metal flashing for window trimming needs to have two bends in it. One bend is for the side of the window facing outward and a bend on each side so that the metal covers the entire wood frame that shows.
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Step 2
Measure on the outside of the window. Since the top corners are 45-degree angles, the inside is shorter than the outside. Always measure for the largest side and cut back if necessary. Push down slightly on the bottom sill when you measure the sides. Remember, measure twice and cut once.
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Step 3
Cut the strip of aluminum metal flashing the length of the window trimming. Now inspect the frame of the window for indentations and angles. The top interior of the frame board meets the top board at a 45-degree angle. Put the metal flashing up against the side board and clip the metal on the interior at the point that the top and side boards meet.
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Step 4
Draw a line using a straight edge from the lower point where you clipped to the top of the trim and use metal snips to cut on the line. This gives the top metal trim the appropriate angle at the top.
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Step 5
Check the bottom sill. The window trimming usually has a cutout where the sill meets the side board. Take the measurements and cut that from the metal flashing.
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Step 6
Clean away any dirt and debris from the existing sill. Clean in the cracks also. Fit the metal flashing to the window trimming. It should snug up nicely. If you are satisfied with the fit, use two or three 1 1/4-inch aluminum trim nails in the appropriate color to attach the flashing.
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Step 7
Follow the same steps for all sides and when done, caulk the corners and seams of the metal flashing.
