Things You'll Need
Wood pine, oak or plywood strip
Sandpaper, medium to fine grit
Circular saw and table
If you have an interior wood door that is too short and lets in drafts, lengthen it with a simple method that will take a few hours. Determine what kind of wood your door is made of, then match it at your local home improvement store in the lumber department. If your door is wood stained, then you can buy stain and varnish there also, or repaint or restain the entire door. Lengthening a short wood door will save on your energy bill, too.
Measure where the door meets the floor when it is closed. Check all the way across, in case one area is uneven in measurement. If there is carpet flooring, remove a 1/4-inch space from the total measurement for easement from the carpet to the door bottom. If the floor surface is flat, remove 1/8-inch space from the measurement for easement. Measure the door width and its thickness, then cut your wood strip to size on the table saw.
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Remove your door by popping out the hinge posts and lay the floor on a table or the floor. If your door bottom is uneven, saw it so it is squared off. If you have a hollow wood door, you won't be able to do this part. Lightly sand the bottom of the door, then wipe with a rag or sponge to remove any residue.
Spread wood glue on both the bottom of the door and on your wood addition. Let it dry for one minute, then gently place together so the pieces match exactly. Your addition should look like part of the door. Screw in four screws evenly across through the bottom piece into the door. Countersink the screws so the heads don't stick out and catch the floor or carpet.
Stain your wood addition to match the door wood as close as possible. If the addition is of significant size, you may need to sand down the whole door and re-stain it so it all looks uniform. If your door is painted, then repaint the whole door so you can't see the new addition. Let the door dry for as long as needed, possibly one day.
Reset the door onto the hinges and set the pins into the hinges to hold the door. Hammer lightly on each pin to sink it properly into place. Test your door by opening and closing it to make sure the installation is even and does not catch anywhere on the floor.
If you know you have to cut your door, then do this before cutting your wood addition.
Always use gloves, eye and ear protection when sawing wood.