Installing Interior Pre-Hung Doors

Basic interior doors (like a bedroom, bathroom, or closet door) are among the simplest installations when it comes to door hanging.  A well-installed door closes tightly, operates smoothly and quietly, and does not swing open on its own.  In addition, your door should be plumb and straight.  This means that a trim is left next to the jamb that is just under ½" wide – which makes measuring and trimming the door prior to installation a must.  The mortises on the door (which are the recesses in which the hinges sit or in which the lockset slides) must also be carefully cut out in order for the door to perform properly – which can be easily accomplished with a keen eye and a sharp chisel.

Trimming the Door to Fit

Determining the door size needed is easy – simply subtract ¼" from the height and the width of the opening for the door.  Measure the door to determine if it must be trimmed.  For trim requirements that are less than ½", planing is advisable; if you're going to be trimming more than ½", use a circular saw for the job.  For trimming the height, trim from the thicker bottom of the door; trimming the width should involve taking an even amount from both sides.  If you're using a circular saw to trim the door, affix painter's tape along the line that will be cut – and mark the line to be cut.  Brace the saw against a cutting guide and trim.

Marking the Hardware Location

Marking the correct hardware location for the door is important. To do this, place the door in the opening and shim until centered.  Check for tight spots and plane or cut as necessary.  Mark the point where the door meets the existing hinge mortises on the door jamb.  Mark the point where the latch hold for the existing strike plate is located (this will be helpful for placing the door knob).

Chiseling Out the Hinge Mortises

Remove the door and position it with the "hinge" side facing upwards.  Using one half of a disassembled hinge, line the hinge up with the hinge mark that you made in the previous step – straight side around ½" from the edge of the door.  Using a pencil, trace the hinge on the door and then hold the hinge's edge against the face of the door.  Draw a line under the hinge.  This will show you how deep you will need to chisel the mortise.  Use a utility knife to score through these lines, being careful to not cut deeper than the guide that's outlined.  Make a series of careful cuts between the lines that you have scored with a mallet and chisel.  Chisel out the wood from the mortise.  Turn the chisel over to where the bevel is facing upwards, and then scrape the mortise until it is smooth and clean.  Use a hinge leaf to check the mortise depth.  Repeat the procedure for remaining mortises.

Drilling a Hole for the Mortise

You will drill a series of holes and then use a chisel to remove the material between them in order to make a pocket for the lockset.  To do this, you can make a guide for your drill using scrap wood.  Clamp the guide in place and use the lock's template to establish the location of the mortise holes. Make the holes with a nail in the center and drill the holes using an auger bit.  You can then chisel a shallow recess for the lock plate.

Hanging the Door

Position one hinge half in the appropriate mortise and then screw the hinge leaf to the door.  Repeat.  Hang the door by attaching the hinges in their slots and slipping in the pins that will hold the door into position.  Install the lockset.