Prehung or split jamb doors come apart so that each side of the trim sandwiches the drywall between the two leaving a seamless installation ready to go with minimal effort. You know you re in great shape if the gap along the hinge side of the door and the top of the door are the consistent one eighth inch.
The height and width must be 1 2 inch greater than the door.
How to install a prehung door. When you set out to install a prehung door begin by measuring the rough opening into which you are placing it. It is best to install shims at the same height as the door hinges. The measurements should match or be no more than 1 4 inch apart.
Use wood shims with the level and tack the shims against the jamb until the level is perfectly plumb. Prehung doors hang on a jamb that is split into two pieces. The opening should be square check this by measuring both diagonals.
The split jamb has a groove under the stop so it can slide over the edge of the main jamb. The opening should be one or two inches larger than the door itself. Typically both jambs are furnished with casings already attached.
Remove the trim molding. Position the prehung door into the rough opening slide it up against the shims and see how things look. To measure the rough opening accurately strip off the old door.
Install prehung door steps. Prehung doors are generally sold by the rough opening the size of the hole in your wall as described later. How to install a prehung interior door parts of a prehung door.
To hang a pre hung door begin by fitting the door into the opening in the wall and making sure the casing around the door is perpendicular to the floor. The rough door opening should be correctly built for prehung door installation. The door is attached to the main jamb which is installed first.
Then anchor the door jamb where you want it by slipping thin wooden shims between the jamb and the top of the door. Pull the door apart while it s lying flat on the ground and set the trim portion aside.