Pre-hung doors come as complete packages that contain the frame, hinges and casing for installation. Doing it yourself usually doesn’t take too much skill or patience – just be sure to use a level to ensure both door and frame remain level!
Begin by applying shims to the hinge side of the jamb and checking that the carpenter’s level bubble is centered.
Measure the Opening
Installing a pre-hung door requires it to be level and plumb; otherwise, its swing may scrape against walls when opened and closed. To properly measure a rough opening (the frame that holds hinges and latch), remove door molding (commonly known as trim) with a pry bar so you can see its true size, measure height from jamb edge to floor by taking measurements at center and both ends, then begin installing.
Make use of a level or plumb bob to check that both walls and trimmer studs are plumb, then shim the head jamb until it meets with the wall level; adjust side jambs as necessary until all are plumb; finally shim latch side jambs such that half of their shim lies above hinge point.
Shim the Jambs
As soon as you’re ready to install your new door, position it in its opening and use a level to make sure it is plumb. If it isn’t, adjust its side jambs with wood shims until they are level with each other and close to meeting up with the top of its rough opening.
Start on the hinge side and tack a shim to the wall behind each jack stud (interior stud that supports door frames on either side) using double-face tape. Check your level against this shim to make sure it is level; if not, move it until it is.
Repeat this process on the latch side until it is also plumb, then nail in place your final shim on the strike side – directly across from hinge side shims – using your level. Check for plumb with your level and nail into place.
Install the Door
Prehung doors differ from slab doors by being assembled as one piece, meaning both door and jambs are connected so they’re ready to swing open or closed with near-perfect alignment. Furthermore, this makes installing hardware such as new doorknobs, locksets and strike plates much simpler.
Once your door arrives, be sure to inspect its size against your opening. If it seems too tall for its intended space, use wood shims to raise its side jamb height so the door fits securely within its rough opening.
Position the door in its frame and use shims to nail it to the studs through shims, before trimming exposed shims and painting or staining as desired. A trained carpenter typically completes this project within one hour; novice carpenters or exterior doors with unpredictable elements could take longer, which makes having someone assist an especially good idea when dealing with large exterior doors.
Finishing Touches
Now that your door has been installed, it is time to complete its trim around its edges and install a lockset and doorknob (if applicable).
Before embarking on any project, ensure you have all of the appropriate tools in hand. A carpenter’s level and hammer will both come in handy; having someone around to help lift heavy objects could also prove helpful.
Assuming you already have an opening measured, begin by measuring with a carpenter’s level and writing down any small measurements you find. Accurate measurements ensure your new prehung door fits the frame properly.
After you have determined the size and shape of your opening, adjust its jambs so they are flush with both walls and level with one another. Be sure to first shim on hinge side, followed by latch side.