How to Frame a Door Opening
Framing a rough opening for an interior or exterior door — sizing the opening correctly, building the header, and installing king and trimmer studs.
Step-by-Step
- 1
Determine rough opening size
The rough opening (RO) for a door is the door unit size plus clearance for shimming. Standard rule: RO width = door width + 2 inches; RO height = door height + 2.5 inches. For a 3/0 × 6/8 door, the RO is 38 inches wide by 82.5 inches tall. Verify with the door manufacturer's spec sheet.
- 2
Mark king stud locations
Mark the king stud locations on the top and bottom plates. King studs run full height from bottom plate to top plate on each side of the opening. They support the header and anchor the trimmer studs.
- 3
Install king studs
Nail king studs to both plates. Use a level to verify they are plumb. King studs must be straight and crown-free — set the crown toward the inside of the opening so the trimmer studs bear squarely.
- 4
Build the header
Build the header from doubled 2× lumber with a 1/2-inch OSB or plywood spacer between them to match the 3.5-inch wall width (in 2×6 walls, use three 2× members or an LVL). Nail the header assembly together with 16d nails every 16 inches. Header size is determined by span and load — verify with a span table or structural engineer.
- 5
Install trimmer studs
Cut trimmer studs to the height of the rough opening bottom. Nail them to the king studs on each side. The trimmer studs carry the header load from above to the bottom plate.
- 6
Set the header
Lift the header and rest it on the trimmer studs. Nail through the king stud into the header end with three 16d nails per side. The top of the header should align with the top of the rough opening.
- 7
Install cripple studs
Fill the space above the header with cripple studs at the same OC spacing as the wall studs. Toenail cripples to the top plate and face-nail or toenail to the header. Cripples maintain the regular stud spacing for sheathing nailing.
- 8
Remove the bottom plate
For door openings, cut out the bottom plate between the trimmer studs with a circular saw. Set the blade depth to just cut the plate without cutting into the subfloor. Make two cuts, remove the middle, and clean up the edges with a chisel.
Pro Tips
- → Mark and cut the rough opening 1/4 inch wider than calculated — doors are much easier to install with a little extra room to shim.
- → Double-check RO dimensions with the actual door unit before framing — catalog dimensions and actual unit dimensions sometimes differ.
- → Use a straightedge to check that king studs, trimmers, and the header all align in the same plane before nailing.
Watch Out
- ! Do not remove a stud in a bearing wall without installing a proper header first — the load above redistributes immediately.
- ! In bearing walls, never use a flat 2×4 as a header regardless of opening size.