How to Install a Prehung Exterior Door
Amp up your curb appeal with a new exterior door. We'll show you how to install a prehung door in just four hours.
An exterior door is heavy, so have it delivered unless you have a truck, and enlist one or two assistants to help you move it into place.
You may need to wait a week or two for delivery of the door that's just right for you. Measure the width of an existing doorjamb or measure the thickness of your rough opening to be sure the jamb is the correct width for your wall; the front interior jamb edges should be flush with your drywall or plaster.
Many prehungs come with brick molding for the exterior, but you may choose to install your own moldings.
Start with a rough opening that is correctly sized and reasonably square, level, and plumb.
What You Need
- Prehung exterior door
- Metal drip edge
- Exterior brick molding
- Interior casing
- Casing nails
- Finishing nails
- Composite shims
- Exterior caulk
- Wood filler
- Fiberglass or foam insulation
- Tape measure
- Tin snips
- Circular saw
- Caulk gun
- Nail set
- Reciprocating saw
- Utility knife
Step 1: Prep Door
Place the door on a smooth surface and remove the hinge and corner guards. If there are plastic inserts or blocks holding the door closed, do not remove them until you set the door in the opening.
Step 2: Level Floor
Check the floor for level and shim if needed. Place a pair of shims — one facing each way, so the surface will be level — every 8 inches or so and nail them in place.
Step 3: Level Door
Uncrate the door and set it in the opening. Check for level and plumb, and shim as needed. Tack (partially drive) nails or screws to hold it in place temporarily.
If a prehung is out of square — that is, if the gap between the door and the jamb is wider on one side — you can usually straighten it. Tilt it so it rests on one bottom corner and pull down as needed.
If a prehung is out of square -- that is, if the gap between the door and the jamb is wider on one side -- you can usually straighten it. Tilt it so it rests on one bottom corner and pull down as needed. If a prehung is out of square -- that is, if the gap between the door and the jamb is wider on one side -- you can usually straighten it. Tilt it so it rests on one bottom corner and pull down as needed. If a prehung is out of square -- that is, if the gap between the door and the jamb is wider on one side -- you can usually straighten it. Tilt it so it rests on one bottom corner and pull down as needed. If a prehung is out of square -- that is, if the gap between the door and the jamb is wider on one side -- you can usually straighten it. Tilt it so it rests on one bottom corner and pull down as needed.
Step 4: Test Door
Check that the door operates smoothly and that the gap between the door and the jambs is consistent all around. To be sure, you may want to install the lockset at this time.
Step 5: Cut Siding
Mark around the door's brick molding for cutting the siding. Or hold the molding you will use in place and mark. Use a handsaw to finish the cuts at the bottom if a circular saw can't complete the cut. Use a chisel at the corners.
Step 6: Attach Felt
Slightly pry away the siding all around and use a reciprocating saw to cut through any nails within 6 inches of the opening. Slip in strips of roofing felt or building paper, wrap them around the framing, and attach with staples.
Step 7: Install Drip Edge
Cut a piece of metal drip edge flashing and slip it up behind the roofing felt. Use a scrap of trim to confirm that you've allowed enough space. The drip edge should incline slightly to direct water away from the house.
Drip Cap Arrangement
Some prehung doors come with a plastic or wood drip cap at the top that is sloped to allow water to flow easily away from the house. If your unit does not have a drip cap, install one. The drip edge flashing fits over the drip cap and slips under the roofing felt or building paper.
Step 8: Caulk
Apply three beads of caulk at the sill plate before you set the door into place. If you have installed shims, apply extra-thick beads to ensure that the threshold will be sealed at all points.
Step 9: Position Door
With a helper, lift the door's threshold onto the caulk (avoid sliding, which would weaken the caulk seal) and tilt the door into the opening. Make sure the brick molding seats against the sheathing.
Step 10: Insert Jambs
Tap in shims as needed all around and check the sides for plumb. Also check that the door operates smoothly and there is a consistent gap between door and jambs all around.
Step 11: Attach Frame
Attach the hinge-side jamb first, using 10d casing nails. If possible, drive the nails where they will be covered with stop molding. Drive nails near the shims and check that the jamb has not become bent.
Step 12: Finish Securing Jamb
Nail the latch side in the same way, constantly checking for a consistent gap between door and jamb -- a piece of cardboard from a note pad makes a good gauge. Nail the header jamb as well.
Step 13: Replace Screws
At each hinge remove two screws and drive in 3-inch screws with the same size heads. These screws add considerable strength and stability to a door.
Step 14: Attach Threshold
Attach the threshold by driving screws into the sheathing. Wipe away any caulking that oozes out. If the threshold has a rubber gasket, install it.
Step 15: Casing Nails
Drive casing nails to attach the brick molding. Use a nail set to drive the heads slightly below the wood surface. Fill the holes with wood filler and sand smooth.
Step 16: Cut Shims
Cut the shims inside. You can often score them with a utility knife and break them off. Or cut them with a handsaw. Cut them flush with the jamb edges, but take care not to mar the jambs.
Step 17: Fill With Foam
Spray nonexpanding foam or gently insert pieces of fiberglass insulation between the jambs and the framing.
Step 18: Kick Board
If siding is exposed below the door, it will be vulnerable to damage by foot traffic. Cut out and replace the siding with a 1x kick board or install the kick board over the siding.