How to Flash Under a Door Sill

Wood is a sturdy and long-lasting building material frequently used in residential home construction. Wood, however, has its weaknesses, and moisture is one of them. According to State Farm Insurance, water damage can contribute to mold growth or rot out your home's sub-floor. Installing flashing underneath your exterior door sills helps prevent moisture damage by stopping exterior moisture from coming into contact with the sub-floor and damaging it over time.

Hammer
Screwdriver
Measuring tape
Self-adhesive flashing
Utility knife

Instructions

- 1
  Close the door. Tap the door's hinge pins loose with a hammer then pull the hinge pins out of the door's hinges. Lift the door away from its hinges. Lay the door flat on the floor or prop it up against a nearby wall.
- 2
  Unscrew and remove the door sill at the base of the door frame.
- 3
  Measure the base of the door frame. Cut three pieces of self-adhesive flashing 6 inches longer than the base of the door frame with a utility knife.
- 4
  Align the first piece of flashing with the interior edge of the door frame. Stick the flashing to the door frame, ensuring that the flashing overlaps enough to cover the interior edge of the door sill. The excess flashing should extend 3 inches beyond the door's threshold on either side.
- 5
  Align the second piece of flashing with the exterior edge of the door frame and repeat the process. The flashing should cover the exterior edge of the threshold to prevent water entry and be 3 inches up on either side of the door frame.
- 6
  Lay the last piece of flashing in the center of the threshold. The final piece of flashing should overlap both the interior and exterior pieces. Smooth out all three pieces of flashing by hand.
- 7
  Cut two 3-inch squares of flashing. Align each square up with the exterior corner of the door frame. Fold each square over the base of the door frame. Smooth out both areas by hand.
- 8
  Examine the door frame. Cover any exposed areas on the door's threshold with flashing. Once the flashing is securely in place, you can re-install the door sill and exterior door.

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