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In this video, Ask This Old House carpenter Nathan Gilbert shows how to close the gap caused by a new floor in an older home with a new threshold.

Steps for Retrofitting a Threshold

  1. Add ⅛-inch to the height of the threshold material, and set a pair of scribes to this measurement. Use the scribes to mark the door on each edge to create a cutline.
  2. Remove the hinge pins from the hinges to remove the door from the jamb. Lay the door flat on a pair of sawhorses.
  3. Using a circular saw, cut the door to the new length using the scribed marks as the cutline. Seal the bottom of the door to prevent the newly exposed grain from absorbing moisture. Rehang the door once it’s dry.
  4. Mark the threshold material to length by holding it in place, butted up against the inside of the door casing on one end, and marking it at the casing on the other end. Cut it to length with a miter saw.
  5. Find the width of the threshold by measuring from the leading edge of where it will sit to the depth of the door casing. Cut it to width on a table saw.
  6. Ease the transition by beveling the top edges of the threshold. Tilt the table saw’s blade to 45 degrees, move the fence toward the blade slightly, and pass the threshold through to bevel one edge. Flip the threshold to bevel the other edge.
  7. If necessary, cut a rabbet in the underside of the threshold with a table saw so that it may overlap the existing flooring.
  8. Hold the threshold in place and use a pencil to mark the cuts for a perfect fit. Do this on both ends of the threshold and cut them out with a jigsaw.
  9. Sand the threshold to make it smooth and apply a coat of sealer to prevent water damage.
  10. Squeeze a small bead of construction adhesive onto the door sill where the threshold will sit. Predrill holes in the threshold 3 inches from either end and one in the middle. Nail the threshold in place.
  11. Close the door to assess the gap under the door. Attach a door sweep to the front of the door with screws to close the gap for a tight seal.

Resources

To bridge the awkward gap between the original threshold and the new flooring, Nathan cut to size a piece of ¾” oak stock lumber, which can be found at any home center.

To cut the board to size, Nathan used a combination of saws, including a TS 55 circular track saw, which is manufactured by Festool and a sliding compound miter saw, which is manufactured by Dewalt.

Nathan secured the threshold to the floor using Gorilla Glue construction adhesive and brad nails.

To help the new threshold blend in with the oak flooring, Nathan applied a polyurethane finish. While most finishes will do the trick, Nathan decided to use a Varathane Clear Semi-Gloss Polyurethane Spray, which is manufactured by Rust-Oleum.

The weatherstripping Nathan used was KC500 1-¼” x 84” Gray Triangular Gasket and Aluminum Screw On Door Weather Strip, which is manufactured by Simply Conserve.


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