Things You'll Need
When replacing doors in your home you might find you want to install taller pre-hung doors. This requires you to make the doorway taller to accommodate the new door. Although a homeowner shouldn't attempt to enlarge an exterior doorway, it's within the scope of the homeowner to make an interior doorway taller. Most interior doorways use standard 2-by-4-inch framing. The key to successfully making a doorway taller is to provide support for the ceiling while you remove the current door header, once you remove the old door and door casing.
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Prepare the Existing Opening
Measure the distance between the floor and ceiling with a tape measure and subtract 1 3/4 inches. Cut a pair of 2-by-4-inch boards to the measurement with a circular saw. Measure the width of the door opening and add 36 inches. Cut another 2-by-4-inch board to that measurement.
Nail the width board to the top of the two height boards with 16d nails. Stand the frame up with the width board against the ceiling and the two height boards evenly spaced around the opening. This serves as a temporary support for the ceiling while you're moving the header.
Pry the jack studs away from the door opening with a crow bar. The jack studs are the trim boards that mount to each door jamb.
Cut the drywall above the door opening even with the rough frame jamb studs and to the ceiling with a utility knife. Remove the drywall in a single piece if possible to reuse once you frame the opening
Remove the header board with a pry bar and hammer. The header board is the horizontal board across the opening. Most interior door frames have a pair of 2-by-4-inch boards on top of each other as header boards.
Pull out the cripple boards with the pry bar and hammer. The cripple boards attach between the header and the ceiling's top plate.
Frame New Opening Height
Add 2 inches to your new finished opening height and cut a pair of 2-by-4-inch boards to the length with a circular saw. For example, if your finished door height is 86 inches the rough door height should be 88 inches. This accommodates for the finished door casing.
Nail one board to the studs on each side of the opening with 12d nails and a hammer. These are your new jack studs. Measure between the two studs above the new jack studs. Cut two, 2-by-4-inch boards to the measurement.
Position one header board on top of the jack studs and between wall studs. Toe-nail the header board to the wall studs with 12d nails. Drive nails through the face of the header board and into the top of the jack studs.
Place the second header board on top of the first. Nail the second board to the first and into the wall studs.
Measure the distance between the top of the header board and the ceiling's top plate. Cut four pieces of 2-by-4-inch board to the measurement. These are your new cripple boards.
Stand one board in between the header board and top plate 1/2 inch away from the wall stud. Toe-nail the board into both the header and top plate. Repeat for the opposite side.
Space the remaining two cripple boards evenly between the first two and toe-nail them into the top plate and header. Remove the temporary support.
Before making the doorway taller, ensure there is enough room on both sides of the doorway for the additional height. Look for low hanging ceiling lights or fixtures before making the decision to install a taller door.
Patch the area between the top of the door frame and ceiling with drywall.
Exterior doorway frame adjustments should be performed by a licensed professional contractor.