How to Install a Prehung Exterior Door
Prepare the rough opening, flash the sill, set the prehung unit in sealant, shim the frame plumb and square, adjust margins, and anchor firmly into wall framing.
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🧰 Required Tools & Equipment
- ✓ 4-foot or 6-foot level
- ✓ Cordless drill and driver bits
- ✓ Hammer
- ✓ Caulk gun
- ✓ Utility knife
- ✓ Tape measure
📦 Materials & Supplies
- ✓ Prehung exterior door unit
- ✓ Composite or cedar door shims
- ✓ Exterior-grade waterproof silicone caulk
- ✓ Self-adhering sill flashing tape
- ✓ 3-inch exterior wood screws
- ✓ 2-1/2-inch exterior casing nails
⚠️ Safety Checkpoints & Warnings
- • Wear safety glasses when driving long fasteners, cutting shims, or using power tools.
- • Prehung doors are heavy and front-heavy when unlatched; keep a helper nearby or brace the slab to prevent it from swinging out unexpectedly.
- • Check for live electrical wiring inside framing before drilling into the rough opening studs.
📋 Step-by-Step Guide (5 Steps)
Inspect and Flash the Rough Sill
Check the subfloor sill with a 4-foot level to ensure it is flat and level, shimming underneath if severely sloped. Apply self-adhering flashing tape across the sill, running it at least 6 inches up both rough jambs and folding it over the exterior wall. Lay three generous, continuous beads of exterior silicone caulk across the prepared sill surface.
- • Flashing tape creates a watertight basin turned 6 inches up each vertical stud.
- • Three parallel, unbroken caulk lines run from side to side across the sill.
- • Failing to level the subfloor before flashing, forcing the door to sit out of square.
- • Leaving breaks in the caulk line where water can seep underneath.
Set the Prehung Unit into the Opening
With the door slab still secured in its frame via the factory shipping plug, tilt the bottom sill of the unit into the rough opening first. Push the top of the frame inward until the exterior brickmould or flange rests tight against the exterior sheathing. Keep the unit centered horizontally with roughly equal 3/8-inch gaps on either side of the jambs.
- • Door sill is fully embedded into the caulk on the subfloor.
- • Even spacing of approximately 3/8-inch visible between rough studs and jambs on both left and right sides.
- • Removing the transport clip holding the slab closed before the frame is anchored.
- • Dropping the door straight down rather than pivoting from the sill, smearing away the sill caulk.
Plumb and Shim the Hinge Jamb
Place a long level against the interior face and edge of the hinge-side jamb. Insert pairs of opposing shims behind each hinge location between the jamb and the rough stud to bring the jamb dead plumb in both directions. Drive a temporary 3-inch screw through the hinge jamb and shims near the top hinge, leaving it slightly proud.
- • Level bubble is centered when held against both the inside face and edge of the hinge jamb.
- • Opposing shims sit flat directly behind top, middle, and bottom hinge locations.
- • Placing single wedge shims instead of pairs, which twists the jamb profile.
- • Over-driving screws and bowing the hinge jamb inward.
Align the Latch Jamb and Set Reveals
Remove the transport clip and open/close the door to inspect the margin around the slab. Insert shim pairs along the latch jamb at the strike plate and top/bottom corners until the gap (reveal) between slab and jamb is uniform (about 1/8 inch) along top and side. Ensure the door slab makes uniform contact with the weatherstripping all the way around when latched.
- • A consistent 1/8-inch margin runs along the top head jamb and down the latch jamb.
- • The door slab compresses weatherstripping evenly without catching or rattling.
- • Ignoring weatherstripping contact, leaving top or bottom corners open to drafts.
- • Shimming the latch jamb too tightly, causing the door slab to bind against the frame.
Fasten Frame and Secure Hinges into Framing
Replace one factory screw in each hinge with a 3-inch screw driven through the jamb, through the shims, and at least 1-1/2 inches into the wall framing stud. Secure the latch jamb by driving 3-inch screws through the jamb behind the weatherstripping and strike plate into the rough stud. Cut protruding shim ends flush with the drywall using a utility knife or flush-cut saw.
- • Long 3-inch screws driven flush through hinge plates directly into structural framing.
- • All shims cut clean and flush with the indoor and outdoor edges of the door jamb.
- • Relying solely on short 1-inch factory hinge screws, allowing the heavy door to sag over time.
- • Breaking shims by snapping them by hand, which splinters the wood and disturbs alignment.
Credit: inspired by an original tutorial by Lowe's Home Improvement — watch the original on YouTube.
Don’t have everything?
- No Self-adhering sill flashing tape? Pre-formed rigid PVC sill pan
- No Composite shims? Cedar wood shims