A prehung door is already hung in a frame. Such doors are mounted on the jambs, so that you do not have to put the hinges, or go through the whole process of squaring the door.
While installing the usual door, you need to buy all the door parts separately and assemble the door before installing it. Prehung door installation is comparatively less complicated, and also helps you achieve a finished and professional look for the room.
- Check the Rough Opening: Start with checking the rough opening of the door with the help of a level. Place the level on the doorway floor and see if the surface is leveled. If not, adjust the level by putting the shims.
- Take the Measurements: Take the measurements of the door opening and note it down on a piece of paper. Go to the local dealer and buy a prehung door that will fit in the door opening appropriately. Make sure that the door design is compatible with the decor of the room.
- Fit the Door in the Opening: After shimming the trimmers, lift the door and place it in the opening. Now push the hinge jamb tight against the shims, so that the door is placed and held well in the opening.
- Adjust the Door: Using the carpenter's square and shims, adjust the door so that it is placed well. Make sure that the door is plumb before you move on to the next step. This is the most important step, because if the door is not well-placed, it may leave unwanted gaps between the door and the opening.
- Adjust the Horizontal Gap: The horizontal gap, also known as reveal, needs to be adjusted well. You have to push or pull the head jamb or head casing to adjust the gap from the top of the door. Also adjust the gap between the door and the jamb on the latch side. Close the door and check if the gaps are even from all the sides.
- Fix the Jamb: Now you have to anchor the jamb. Add some shims between the main jamb and the trimmer near the top of the door opening, and nail them to the trimmer with the 8d finish nails. You also have to nail the shims near the base and the strike place.
- Replace the Hinge Screw: It is important to save the door from sagging, and you must fix it tightly. For this, remove one of the screws from the hinge of the door, and replace it with a big crew that is long enough to penetrate the trimmer.
- Attach the Split Jamb: Now, attach a split jamb. Attach both the jambs together using the 8d finish nails. Cover the joint between the two jambs with the stop molding. Make sure that the nails pass through the stop and trimmers. Fill the holes with the wood putty.
Attach the door hardware such as door knobs, latch, locks, and handles, to give a finished look to the door. Once the installation is complete you can paint or polish the door as you like. The procedure for interior and exterior prehung door installation is almost the same, though not exact, and needs a lot of precision.