How to Replace the Gasket on a Bottom Exterior Door

Remove the screws from the existing door sweep. If the sweep is flat, it will fall off when you remove the screws. If it is U-shaped, open the door and slide off the sweep. Take the old sweep with you to purchase a new one. Choose a replacement with screw holes that match up with the holes in the old one.

Measure across the bottom of the door. Transfer that measurement to the new door sweep and make a mark with a marker. Cut the metal strip of a flat sweep at the mark with metal shears. Complete the cut through the rubber fin at the bottom of the strip with a sharp utility knife. Cut a U-shaped sweep to the correct length with metal shears. Rub a metal file or rasp along the cut metal to dull any sharp edges.

Align the screw holes of a flat sweep with the holes in the door and insert one screw through any hole on the strip. Twist the screw clockwise by hand. Insert the remaining screws loosely with the screwdriver. Open and close the door. If the rubber fin touches the threshold but does not get caught on it, tighten the screws on the sweep.

Open the door and slide a U-shaped door sweep onto the bottom of the door to install it. Align the screw holes and insert the screws loosely. Close the door to check the fit. Slide the sweep up or down to adjust it. Trimming the short fins of a U-shaped sweep is not advisable.

Adjust a flat sweep if it prevents the door from moving properly. Slide it up or down to adjust it then tighten the screws to hold it in place. If adjusting does not help shorten it, remove the sweep. Trim a small amount of rubber off the bottom of the fin with the utility knife then reinstall the sweep.