How to Set a Prehung Door: Shim, Level & Secure the Frame
By WholesaleDoorHub Team · May 2026
Direct answer: Installing a prehung interior door takes 20–40 minutes for an experienced installer. The critical steps are: set the unit, shim at hinges and strike, fasten through jamb, check reveal, and install casing.
Step-by-Step: Setting, Shimming & Fastening a Prehung Door
Tools Required
| Tool | Purpose |
|---|---|
| Level (4-foot) | Plumb check |
| Drill + 3" screws | Fasten jamb |
| Shims (cedar) | Fill gaps |
| Utility knife | Score shims |
| Finish nailer | Install casing |
| Tape measure | Check reveal |
Step 1: Prepare the Rough Opening
Check the rough opening for plumb and square. If the rough opening is out of plumb by more than 1/2", correct before proceeding. A plumb rough opening makes installation significantly faster.
Step 2: Set the Unit
Remove the shipping straps. Set the prehung unit in the rough opening. Center it side-to-side, leaving equal gaps on each side.
Step 3: Shim at Hinge Locations
Place shims at each hinge location on the hinge jamb. Drive a single 3" screw through the hinge jamb at each shim. Check plumb after each screw.
Critical: The hinge jamb must be plumb. All other adjustments depend on this.
Step 4: Shim the Strike Jamb
Close the door. Check the reveal (gap between door and jamb) — it should be consistent at 1/8" from top to bottom. Shim and fasten the strike jamb to achieve this.
Step 5: Fasten the Head Jamb
With both side jambs fastened, check the head jamb. It should be level and the reveal at the top of the door should be consistent. Shim and fasten as needed.
Step 6: Check Door Operation
Open and close the door. It should swing freely without binding. The latch should engage cleanly. If the door rubs at the top, the strike jamb needs adjustment.
Step 7: Install Casing
Score and snap protruding shims flush. Install casing on both sides with a consistent 3/16" reveal on the jamb.
Common Prehung Door Installation Mistakes
| Mistake | Result | Fix |
|---|---|---|
| Hinge jamb not plumb | Door swings on its own | Re-shim and re-fasten |
| Screws without shims | Jamb bows | Always shim before fastening |
| Reveal inconsistent | Door rubs frame | Adjust strike jamb |
| Casing nailed to door | Door won't open | Nail casing to jamb and wall, not door |
FAQ
Q: How long does it take to install a prehung door?
A: 20–40 minutes for an experienced installer. First-time installers should budget 45–75 minutes.
Q: Do prehung doors need to be shimmed?
A: Yes. Shims are essential for transferring load and achieving plumb. Never fasten through the jamb without shims.
Q: Can prehung doors be installed in out-of-plumb walls?
A: Yes. Shims compensate for walls that are out of plumb. The door unit itself can be plumb even if the wall is not.
Get Wholesale Pricing
48-hour quote turnaround. No minimum order on in-stock items.