While looking for doors, you will find two completely different styles: slab doors and prehung (pre-hung) doors. This difference mostly goes to light as you plan to buy and install the door by yourself, without calling specialists. In fact, if you purchase not the proper door type, it will not suit your doorway.
A prehung door is a door slab with frame, which is already connected by hinges to a doorframe and ready to be installed into a doorway. Manufacturers usually sell it as a full and complete package. However, the customer can add some features and accessories later.
A prehung door is usually more expensive than a slab doors that features a self-contained piece with a frame that can be installed in a prepared doorway.
Before selling, pre-hung door is properly packaged and tightened to the frames. Usually, a polyester tension straps used for packaging. Plastic spacers also prevent the doors from twisting and damaging in time of delivery.
Prehung door installation is a demanding and sometimes difficult process. It is even more difficult with the entry pre-hung doors, as they need a precise tightness due to extreme weather conditions. Entry doors are usually heavy to transport, move and install into prepared doorway. Today, you can find modern and retro style exterior and interior door models come in a format of pre-hung door.
Please note: If you already have an installed doorframe you need a door slab. The exception can only be if you plan to remove it to the bare studs.
Door opening
Prehung doors are made to fit rough openings 2 to 2 1⁄2 inches bigger than the corresponding dimensions of the jamb. The jamb’s depth should match the thickness of the wall, including the plaster or drywall. If the opening already exists, check that the trimmers are plumb, parallel, and square to the wall and the header.
The swing direction
Before ordering you have to know which way you want the door to swing, and/or left-hand or a right-hand door you need. In other words, which side you want the knob to be on when opening the door toward you.
Installation
Check the rough opening - place a level on the floor in the doorway. If the hinge side is lower than the latch side, slip shims under the level nearest the hinge jamb. Adjust until the level's bubble is centered. Check the walls and the trimmer studs for plumb using a level or plumb bob. Also, check the trimmers' faces with a framing square to see if they are square to the wall. Check that the trimmers are parallel by measuring between them at the top, bottom, and middle of the opening.
Shim the trimmers - on the hinge jamb, measure from the bottom of the jamb to the center of each hinge. Mark the hinge locations on the hinge-side trimmer by measuring up from the floor.
Fit door into opening - lift the door into the rough opening and push the hinge jamb tight against the shims tacked to the trimmers.
Adjust the gap between the door - check the horizontal gap, or "reveal," between the top of the door and the head jamb. It should be uniform from left to right and 1/8- to 3/16-inch wide. Open and close the door to check that its leading edge, the one that rests against the stop, clears the jamb by a consistent 1/8 inch.
Anchor the jamb - slip a pair of shims between main jamb on the latch side and the trimmer, near the top of the door opening. When they are just touching the back of the jamb without putting any pressure on it, nail them to the trimmer with finish nails. Nail additional pairs of shims a few inches above the base of this jamb, as well as just above and below the strike plate.
Replace hinge screw - remove the center screw from the top hinge leaf and replace it with a screw that's long enough to penetrate the trimmer. This prevents the door from sagging and binding.
Attach the split jamb - from the bottom part, gently push the edge of the split jamb into the groove in the main jamb. Tap the two jambs together using both hands.
Mount the latch hardware.
Pros of prehung doors
Prehung option makes the newly installed unit work simple and quick. In case if the planned area for the door is exposed and open, you are going to find it simple for installing a pre-hung door. As its package is already complete – with its own frame. In case, you were considering a purchase of a slab door, you would need to complete all the framing work by yourself. While it is not really a difficult task, you will spend more time and effort for the entire project.
Cons of prehung doors
A prehung door can weight from 40 to 120 lbs. so, they are heavy and difficult to install. The pre-hung door with a hollow core – the lightest pre-hung door you can purchase. In case if the weight is not a problem for you, a pre-hung door is usually big and inconvenient to move. Usually, two workers are required to install such a unit. The other problem is the size of a transportation vehicle. You must have enough room to place a whole slab with framings. The installation process is simple itself, but it also can be difficult to position the door correctly.
Tips:
During the installation of a pre-hung door, don’t unwrap the packaging materials, including tensions straps, till the unit is already installed. We also recommend to keep the pre-hanging clips so the door does not open when you are installing it
Use 8d finishing nails through the frame, through the shims and into the studs