Although it seems a more daunting project than hanging a slab door, installing a prehung door is actually the easier route to go. Because the door comes already attached to its hinges and fitting in the jamb, the hard work is done. It's a straightforward job that can be done single-handedly, although it is easier with a helper.
Installation of an exterior door takes more expertise and may be too difficult for a beginniner. Here, we'll refer only to interior doors. Check out About.com's Home Renovation channel for information on the difference between prehung and slab doors.
Before You Install a Prehung Door
Measure carefully so you only have to make one trip to the store. You'll need the length and width of the raw door opening as well as the thickness of the wall. Check the labels for the door that matches your specifications.
You'll also need:
- A 4-foot level
- Wood shims
- 4d and 8d finish nails
- Coping saw
- Lockset (door handle and hardware)
- Safety glasses
How to Install a Prehung Door
- A prehung door comes packaged in wood bracing; remove those and all the packing material.
- Stand the closed door and frame assembly in the center of the opening and hold the level vertically against the casing on the hinge side.
- Start inserting shim pieces between the jamb and the rough opening on the hinge side of the door until the jam is plumb, or absolutely vertical, according to your level. Do not just match the jamb to the rough opening, because you'll only cause trouble for yourself later in the project. Place overlapped shims at the hinge locations to give the screws a good grip, and anywhere else you need to keep the level's bubble between the lines.
- When you've got the hinge-side jamb plumb, drive an 8d nail into the doorframe close to the topmost hinge, through the jamb as well as the shim. Repeat the process for the other two hinge areas. Then check again for plumb on the hinge-side jamb.
- Do the same thing on the other jamb; check it with a level, insert shims where needed and nail through them. If there's an appreciable gap between the top of your doorframe and the rough opening, shim that and nail through as well.
- Check again for plumb and level on all three sides; don't brush off a slight discrepancy, because it will cause you trouble down the road. It's better to pull out nails and rearrange shims now, rather than to have a door that won't shut properly.
- Once the assembly is level and plumb, nail around the frame every 18 inches with 4d nails. Tap the nailheads into the surface with a nailset. Most professionals will remove the center screw form each jamb hinge and replace it with a longer screw to provide more holding power and keep the door from sagging.
- Install the lockset according to package directions in the precut openings. You may find that the precut mortises may need a little tweaking to fit your hardware; if that's the case, scribe the outline with a sharp utility knife and chisel out the waste to the same depth as the existing mortise.
- If you saved the molding from the old door, reuse it to trim the new door. Otherwise, measure carefully and use a miter saw or handsaw and miter box to cut 45-degree angles on the new trim. Test for proper fit around the doorway, then secure with finish nails. Set with the nailset.
- Finally, go back and fill in all the nail holes with putty. When dry, sand carefully, then stain or paint the wood.
- Don't rush the job; getting the frame plumb and level is absolutely key. An off-kilter frame will make a door swing open or keep it from closing altogether.
- Measure the doorknob opening as well as the door's thickness before you buy the new lockset, and check the lockset packaging for compatibility.