Tools & Materials 
Level
Hammer
Handsaw
Prehung interior door
Wood shims
8d casing nails
Protective equipment
Install prehung interior doors after the framing work is complete and the wallboard has been installed. If the rough opening for the door has been framed accurately, installing the door takes about an hour.
Standard prehung doors have 4 1/2-inch-wide jambs and are sized to fit walls with 2 × 4 construction and 1/2" wallboard. If you have 2 × 6 construction or thicker wall surface material, you can special-order a door to match, or you can add jamb extensions to a standard-sized door (see Tip, next page).
Tools & Materials
Level
Hammer
Handsaw
Prehung interior door
Wood shims
8d casing nails
Protective equipment
Prehung doors save you time and effort during installation because the jamb is already installed on the door.
HOW TO INSTALL A PREHUNG INTERIOR DOOR
Slide the door unit into the framed opening so the edges of the jambs are flush with the wall surface and the hinge-side jamb is plumb.
Insert pairs of wood shims driven from opposite directions into the gap between the framing members and the hinge-side jamb, spaced every 12". Check the hinge-side jamb to make sure it is still plumb and does not bow.
Anchor the hinge-side jamb with 8d casing nails driven through the jamb and shims and into the jack stud. You may want to predrill the nail holes to prevent splitting the shims.
Insert pairs of shims in the gap between the framing members and the latch-side jamb and top jamb, spaced every 12". With the door closed, adjust the shims so the gap between the door edge and jamb is 1/8" wide. Drive 8d casing nails through the jambs and shims into the framing members.
Cut the shims flush with the wall surface using a handsaw. Hold the saw vertically to prevent damage to the door jamb or wall. Finish the door and install the lockset as directed by the manufacturer. Install trim.
Tip 
If your walls are built with 2 × 6 studs, you’ll need to extend the jambs by attaching 1"-thick wood strips to the edges of the jamb after the door is installed. Use glue and 4d casing nails when attaching jamb extensions. Make the strips from the same wood as the jamb.
