How to Install Z Flashing Above an Exterior Door

Measure the width of the doorway using a tape measure. Make sure you measure the entire width of the door casing above the door, as you’ll need to cover the casing with the flashing for it to be effective. Add 2 inches to the measurement so that you’ll have enough of the flashing to cap the ends of the casing.

Cut the Z-flashing using the adjusted measurement with a pair of tin snips. Cut along the bottom seam of the Z-flashing, the one along the joint between the top of your door casing and the front of the door casing, 1 inch from each end of the flashing to create the material needed to cap the side of the door casing.

Make a 45-degree angled cut in the house wrap above the door casing with a utility knife. Start the cut at the corner of the casing and then angle it away from the casing and upward, about an inch to allow you to slip the top of the flashing beneath the wrap. Fold the wrap upward against the wall at the cut to reveal the wooden cladding beneath. Tap the folded wrap in place with masking tape.

Place the flashing against the wall above the door casing so that the bottom of the flashing overhangs the front of the casing while the top panel of the flashing lies flush against the wall. When in place, it will look like a horizontal “Z.” Make certain the flashing is centered on the casing, with the two cuts in the seam extending to both sides of the casing ends.

Tap downward with a hammer on the cut piece of flashing extending over the top of both sides of the door, so that the pieces fold over the edges of the casing. The cut seam should allow you to hammer it down without affecting the positioning of the rest of the flashing. There will be a small piece of the now-bent flashing extending forward from the casing side. Hammer it over the side of the casing so that it overlaps the front of the door casing, creating a small cap.

Nail the top of the Z-flashing to the wood sheathe around the structure. Place the nails about 2 inches above the casing, through the flashing and into the sheathing. Place a nail every 6 inches along the flashing.

Remove the masking tape and lower the building wrap back into place. Place a bead of caulking at the angled cut beneath the wrap to hold it in place and seal the cut. Smooth the caulk with your thumb.

Cover the cuts with self-adhesive building tape to complete the seal. You can begin installing the wall cladding overlapping the flashing after installation.