What happens when you replace a door

Door replacement means removing an old door and frame from the opening and installing a new one in its place. The job involves taking out the old door, hinges, and frame; measuring the opening; fitting a new pre-hung door unit (frame and door together) or installing a slab door into an existing frame; and sealing gaps with caulk and trim. Most interior doors take two to four hours. Exterior doors take longer because they need weatherproofing and may require adjustments to the threshold.

You will need basic tools: a hammer, pry bar, level, drill, saw, measuring tape, and a utility knife. The most common mistake is not checking whether the opening is square before you start—a crooked opening means the new door will stick or not close properly. The second mistake is forcing a door that does not fit instead of shimming it into place.

Key Takeaways

  • Measure the opening width, height, and depth before you buy a door, because openings are often not perfectly square and doors come in standard sizes.
  • A pre-hung door (frame and door together) is easier for a first-timer than a slab door, because you do not have to hang hinges yourself.
  • Use shims—thin wooden wedges—to keep the frame level and plumb while the caulk and fasteners set, rather than forcing the door to fit.
  • Interior and exterior doors need different installation steps: exterior doors require a threshold, weatherstripping, and caulk to keep water out.
  • If the opening is damaged or out of square by more than one-quarter inch, you may need to repair the frame before the new door will close properly.

Measuring the opening and choosing the right door

Before you buy anything, measure the opening three times: width at the top, middle, and bottom; height on both sides and in the middle; and the depth of the frame from inside to outside. Write down the smallest width and height—that is what the door has to fit into. Standard interior doors are 32 inches wide by 80 inches tall; standard exterior doors are 36 inches wide by 80 inches tall. If your opening is smaller or larger, you will need a custom door or you will have to adjust the opening itself.

Check whether the opening is square by measuring diagonally from corner to corner. Both diagonal measurements should be the same. If they differ by more than one-quarter inch, the opening is out of square and you will need to shim the new frame to make the door close properly. Take a photo of the opening and the measurements with you when you shop, so the staff can confirm the door will fit.

Decide between a pre-hung door and a slab door. A pre-hung door comes with the frame and hinges already attached—you just set it in the opening and shim it level. A slab door is just the door panel; you install it into an existing frame or build a new frame yourself. Pre-hung doors cost more but are much faster for a first-timer.

Removing the old door and frame

Close the door and remove the hinges by unscrewing them from the frame. If the screws are stuck, spray them with penetrating oil and wait 15 minutes. Once the hinges are off, lift the door out and set it aside. If the door is heavy, have someone help you—a standard door weighs 30 to 50 pounds.

Next, remove the trim (the molding around the frame on both sides). Use a pry bar to gently lift the trim away from the wall, starting at the middle and working toward the corners. Work slowly so you do not crack the trim or damage the wall. If you want to reuse the trim, be extra careful.

Once the trim is off, you can see the frame nails. Use the pry bar to pull the frame out of the opening. Start at the bottom and work your way up. The frame may be caulked or nailed in place, so you may need to cut through caulk with a utility knife first. Once the frame is out, clean out any old caulk, nails, or debris from the opening.

Installing a pre-hung door in the opening

Set the new pre-hung door unit in the opening. Do not nail it yet. Place a level against the frame on the hinge side (the side where the hinges are). If the frame is not plumb (perfectly vertical), use shims—thin wooden wedges—under the bottom of the frame to raise it until it is level. Tap the shims in gently with a hammer. Check the level again after each tap.

Once the hinge side is plumb, check the top of the frame with a level to make sure it is level (horizontal). If it is not, add or remove shims at the bottom until the top is level. Then check the latch side (the side opposite the hinges) and shim that side plumb as well.

When the frame is level and plumb on all sides, drill pilot holes through the frame into the studs (the wooden posts behind the wall) and drive screws through the frame into the studs. Use at least two screws on each side, one near the top and one near the bottom. Do not use nails—screws hold better and are easier to remove if you need to adjust.

Sealing and finishing an interior door

Once the frame is screwed in place, remove the shims and fill the gaps between the frame and the wall with caulk. Use paintable caulk so you can paint over it to match the wall. Run a bead of caulk along the inside edge of the frame where it meets the wall. Smooth it with a wet finger or a caulk tool. Let the caulk dry according to the package directions—usually one to three hours.

Install the trim back on both sides of the door. If you removed the old trim carefully, you can nail it back in place with finishing nails. If the trim is damaged, buy new trim that matches the style and width of the trim in the rest of the room. Nail the trim to the frame, not to the wall, so it moves with the door frame if the house settles.

Once the trim is on and the caulk is dry, paint or stain the frame and trim to match the rest of the room. The door itself usually comes pre-finished, but check the package to be sure.

Sealing and finishing an exterior door

Exterior doors need extra steps to keep water out. After the frame is screwed in place and before you install trim, explore weatherstripping around the inside of the frame. Weatherstripping is a foam or rubber seal that compresses when the door closes, blocking drafts and water. Most weatherstripping comes with adhesive on the back—peel and stick it to the frame where the door will touch it when closed.

Check the threshold (the piece at the bottom of the door). If the old threshold is damaged, remove it and install a new one. The threshold should slope slightly toward the outside so water runs away from the house. Caulk around the threshold where it meets the frame and the floor.

explore caulk around the outside of the frame where it meets the wall and the siding. Use exterior-grade caulk that can expand and contract with temperature changes. Smooth it with a wet finger. Once the caulk is dry, install the exterior trim and paint or stain it to match the house.

Testing the door and fixing common problems

Close the door and check that it closes smoothly without sticking or rubbing. If it sticks at the top, the frame may not be plumb—use shims to adjust it. If it sticks at the bottom, the threshold may be too high—you can sand it down slightly or shim the frame up a little. If the door does not close all the way, the frame may be too wide—remove the shims and re-shim more carefully.

Check that the door latches properly and that the deadbolt (if there is one) lines up with the strike plate on the frame. If the latch does not catch, the strike plate may need to move up or down slightly. Loosen the screws on the strike plate and slide it into the correct position, then tighten the screws.

If the door swings open or closed on its own, the frame is not level. Use a level to check again and adjust the shims. This is a safety issue—a door that swings on its own can pinch fingers or cause someone to trip.

Frequently Asked Questions

Do I need to remove the old frame or can I install a new door in the existing frame?

You can install a slab door in an existing frame if the frame is in good condition and the opening is the right size. If the frame is damaged, warped, or out of square, replacing the frame with a pre-hung door is faster and gives better results. Replacing the frame also lets you upgrade to a better-insulated frame if you are replacing an exterior door.

What if the opening is larger than the standard door size?

If the opening is wider than a standard door, you can build out the frame with additional studs and trim to make the opening smaller, or you can order a custom-sized door. Building out the frame is cheaper but takes more time. Custom doors cost more but fit perfectly. For heights, you can add trim above the door to fill the gap, or order a custom height.

Can I install a door by myself or do I need help?

You can install an interior door by yourself—it is a one-person job. For an exterior door, having a second person to help hold the frame level while you shim and screw it in place makes the work faster and easier, but it is not required. The hardest part is holding the frame steady while you work, so a helper is useful but not essential.

How long does it take to replace a door?

An interior door takes two to four hours from start to finish, including removing the old door, installing the new one, caulking, and installing trim. An exterior door takes four to six hours because of the extra weatherproofing steps. If the opening needs repair or the frame is out of square, add another two to four hours.

What is the difference between interior and exterior door installation?

Exterior doors need weatherstripping, a threshold, and exterior caulk to keep water and drafts out. Interior doors do not. Exterior doors are also thicker and heavier, and the frame is usually deeper to accommodate insulation. The basic installation steps are the same, but exterior doors require more sealing and finishing work.