With careful planning and the help of some quality tools, it should be possible to install a pre-hung door in one day. Gather materials such as wood shims, 4d and 6d finish nails, trim to match existing casing, etc. before starting this task.
Center the frame in your rough opening and secure it by shimming its hinge side shim. Additionally, adjust any required head jamb adjustments and use a level to check alignment.
Measure the Rough Opening
Before installing a prehung door, it’s essential that its frame fits precisely. To do this, measure the rough opening – that area on which the new door will go into – which includes existing wall framing that will receive it.
To determine the rough opening dimensions, use a carpenter’s level to check each jamb’s height. If one hinge side is lower than another, slip shims under each jamb until the bubble of your level is centered before tacking them in place with finish nails.
Measure the Door
Before installing your pre-hung door, double check its dimensions are accurate. Use a tape measure to get measurements for width and height – using stud to stud measurements for width measurement as well as top of frame to floor surface measurement for height.
Check your frame with a carpenter’s level to ensure it’s level and plumb, if not, use shims as necessary to shim it so your door hangs correctly and clears any flooring you might be installing.
Measure the Jambs
Once your shims have been installed, use your level to confirm that the jamb’s strike side is square with itself. If it isn’t, add more shims on both the middle and lower areas until your bubble on your level has settled into its center position.
Add shims to the latch side of each jamb jam, directly across from each hinge, securing them using finish nails.
Cut the Jambs
Once your door has been aligned precisely as desired with its jambs and side stops have been secured with nails, use a utility knife to trim away any remaining shims and prepare your head stop and jambs for casing.
Use a level to ensure the hinge-side jamb is plumb (or vertical). Shim above it as needed until its bubble centers on your level; repeat for latch-side jamb. Fasten frame to rough opening at each shim location.
Install the Jambs
Once both side stops are in place, door jambs are ready for casing installation. Shim the hinge side against the wall using wooden shims while using your level to ensure plumbness.
Apply the same process when working on the latch side of a jamb. Continue adding shims until your frame is square and plumb; if necessary, replace one factory screw per hinge with longer screws for optimal results; cover nail heads with putty to keep your finished product looking professional.
Install the Door
Your doorknob and lockset, along with some trim designed specifically to match it will all be needed for assembly.
Working together, position the doorframe against the rough opening and use shims between it and studs at hinge locations and from top to bottom on latch side for adjustment.
Attach the top hinge-side bracket first and use a level to mark where its drawn line crosses through an alignment notch on the second bracket.
Install the Hardware
Once your door is installed and its shims tacked down, the next step should be installing any required hardware such as hinges, locksets, panic devices and closers. In addition, consider picking up trim and door stops at this time as well.
Put a 4-foot level across your doorway and adjust the casing until it is level and plumb, using finish nails driven into studs through its casing to secure it. Caulk any seams between frame and trim as necessary to finish off this project successfully.
Finishing Touches
After you have installed your drywall, inspect each hinge location of the casing to see if it rests flush against the wall. If not, shim it and nail through to trimmer stud to secure. Use putty to hide nail heads.
Installing interior doors is a do-it-yourself-friendly project that can transform living spaces. Even though pre-hung doors may be simpler to install than slab ones, careful adjustment for proper fit must still be performed for proper functioning. If in doubt, seek professional assistance.