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How to Install a Frost King Adjustable Threshold

Paul Massey

Frost King is a leading manufacturer of door and window weatherstripping, and produces adjustable exterior door thresholds designed to be an effective barrier to drafts, dust and insects.

They are a viable replacement where a standard door drip cap will not seal the gap under the door, or for new door installations in which an improved weather seal is desired.

  1. Clean the door’s threshold area of any dirt or debris.

  2. Measure the width of the door opening at the floor between the face of the vertical jamb on both sides. Mark this dimension on the threshold and use a hand square to extend the mark. If more than 1 inch needs to be trimmed from the threshold, measure the dimension from the center of the threshold and cut an equal amount off of each end.

  3. Cut the threshold to length with a hacksaw. Complete the final cut with a utility knife.

  4. Insert the threshold into place with the door open and verify the correct fit. Each end of the threshold should fit tightly to the jamb. The weatherstrip should be centered beneath the door, with the front edge aligned with the door stops on both sides. Remove the threshold from the door opening.

  5. Run a continuous 1/2-inch bead of silicone caulking across the door opening, aligned with the front edge line of the door jamb.

  6. Open the door and slide the threshold evenly into position, raising the front edge slightly to clear the silicone caulking. Lower it to spread the caulking for a complete seal. Insert the threshold to where the adjustable vinyl strip is centered beneath the closed door position. Trim the door stop if it impedes the proper positioning of the threshold.

  7. Secure the threshold to the floor of the door opening with the screws provided. Insert one screw at each of the predrilled holes and tighten them until the threshold is held firmly to the floor. Wipe away any excess silicone caulking that squeezes from beneath the threshold.

  8. Adjust the weatherstrip by turning the adjustment screws, as necessary, to seal the gap beneath the door. Turn the adjustment screws counterclockwise to raise the weatherstrip or clockwise to lower it until the weatherstrip presses firmly against the door bottom when the door is closed.