Installing a prehung door these days is easier than its
ever been. In the days before prehung doors, it took more tools
and knowledge to hang a door than it does now.
Imagine getting a door slab, an unassembled door jamb,
hinges and door hardware and having to do all the mortising,
drilling, rabbeting on site. No longer do you need an array of
tools such as a drill, a mortising jig for hinges, strikes, and
bolt plate. No jig for drilling the backset for the doorknob
and bolt. Nowadays all you need is a hammer and hard trim nails
or a finish nail gun and some shims.
The first thing you need to do is check the opening you'll
be hanging the door in for the correct size. It should be 2"
bigger than the door size. Even though it's a rough opening it
should be reasonably plumb and square.
If the opening was framed by someone else, you may want to
break out your level and framing square and check this also.
Drywallers sometimes believe the rough opening was meant for
them and will let the drywall run into the opening. If this is
the case use a drywall saw or sawzall to cut it back.
Once all the vitals have been checked your ready to hang a
door. Prehung doors come assembled a couple different ways.
They can be bought with trim already mitered and nailed on to
one side and without trim. If there is no trim installed, I
like to put it on before I put the door in the opening. The
trim is installed on the hinge side.
Most doors open into a room and against a wall. When putting
the door into the opening, try to put the door in the center of
the opening. The door jamb should be able to move to the left
and right in the opening. The gap between the door and jamb on
the hinge side is usually about an 1/8" of an inch. This
dictates the gap or space you should have all around the door.
Move the door jamb to the left or right until you have that
same space at the top. You then nail the trim on the top hinge
side and the bottom hinge side. Then nail the strike side on
the top making sure you still have an equal space. Nail off the
rest of the hinge side with 3 or 4 more nails. The 2 nails
already in the top are all I usually put in. Now nail the rest
of the strike side starting at the top and working your way
down, maintaining the same space as the top and hinge side.
Once the prehung door is nailed into the opening on the
inside, it's time to shim the door jamb. First, pull the door
closed to make sure it hits the door stop evenly on the strike
side. If it is hitting only at the top pull the hinge side
toward you till it hits even. If it hits only at the bottom,
push the hinge side jamb away from you till it hits evenly.
Once you get the jamb aligned put shims between the jamb and
stud opening, being careful not to bow the jamb into the
opening. If need be use a straight edge to keep it
straight. I put shims behind every hinge and the strike and
also at the top and bottom of the strike side. I nail these
shims in with two nails, one on each side of the
The next step is to apply the door casing to the outside of
the door. Once this is done, your ready for the door hardware.
If everything went right, the bolt should engage the strike
plate and the door should fit snuggly against the