Prehung doors are a simple and efficient way of installing a doorway. They are easily bought in a large variety of styles and sizes. A home improvement store or hardware store has numerous prehung doors in stock. Typical prehung doors come in 30, 32, and 36 inch sizes, but there are many sizes for special order doors to be made. When selecting a door, measure the opening and subtract two inches for the door size, For example if you have a 32 inch wide rough opening for your doorway, then a 30 inch door is the correct size you will need.
There aren’t a lot of tools required for hanging a door. You need finish nails, a hammer, a nail set, level, and shims. If you’re hanging a prehung door for the exterior, you will need to use a caulk gun and caulk for under the threshold.
First, level the rough opening on both sides as well as the top. Adjust the sides and top as needed to make sure the rough opening is as level as possible. Level the header best that you can also. Place the level on the floor too, just to get an idea of how it will react to the door. Most interior floors are level, but doors near plumbing fixtures or other penetrations in the slab tend to be slightly unleveled.
Pull the door apart at the jambs. Usually a small nail or staples hold the jamb in place, so care is required when removing them, so as not to damage the casing around the door. Remove the door nut which hold the door in place from swinging out during shipping. It is usually in the striker hole and is screwed into place through the handle hole. In some doors there is a screw inserted through the frame into the door. Make sure the door swings freely before you insert it into the rough opening. After you remove the case from the door and make sure it opens properly, put the door half into the rough opening taking care to ensure it swings the proper way. Center the door into the rough opening. Insert any shims under the door case to counter any of the slab floor that may be out of level.
Shim the door way with five sets of shims along each side of the opening. One set of shims above each hinge and one set at each end of the door, top and bottom. If more than one shim is required make sure the shims are flat in the door and stacked alternate to each other. Insert a finish nail into each corner of the hinge side of the door. Close the door almost all the way and place a level on the door it self, not the case. Shim the hinge side until the door is level. Close the door entirely and check for reveal. If the reveal is the same around the hinge side of the door, then nail through the shims with a finish nail into the rough opening. Make any adjustments to the shims before nailing. Repeat the process on the other side by closing the door and checking the reveal is the same the entire length. Make sure the door jamb is flush with the drywall or finished wall exterior.
Once the door is secure, place the other half of the case into its provided slots and squeeze until its tight against the walls surface. Attach with finish nails into the wall. Check the door to make sure it closes and opens properly. Set all the nails with a nail set. Use wood putty to fill any holes left from the nail set and paint or stain as needed.