How to Fit a New Door into an Old Opening
Replacing a door isn't difficult—but it will require a little reconfiguring. We'll show you the easiest way to add a new door while using the old door's opening.
If an existing door is damaged or worn, you can put a new door into the doorway. Often the easiest way is to remove the existing jambs and casing and install a prehung door. However, if the doorway is square or if the existing trim is difficult to replace, you can keep the doorway and replace the door.
Unless your house is very old, you'll have little problem finding doors to fit. The most common door height is 80 inches, although most are available 78 inches tall as well. Common interior door widths are 24, 28, 30, 32, and 36 inches. Height and width are often stated in feet and inches: 2-6 for 30 inches or 3-0 for 36 inches, for instance.
Before you begin, remove the old door and check that the doorway is square. If not, scribe and plane the door. If the doorway is well out of square, remove the casing, cut through the nails holding the jambs, and reattach the jambs so they are square.