Installing interior doors is a manageable DIY project with the right tools, materials, and step-by-step approach—whether you’re replacing an old door or installing a new one in a framed opening. Proper installation ensures the door operates smoothly, closes securely, and aligns with the frame, preventing gaps that cause drafts or noise. This guide covers the key steps for installing a pre-hung interior door (the most common type for DIYers, as it comes with a frame and hinges attached), though the process can be adapted for slab doors (which require attaching hinges to the frame and door).

Step 1: Gather Tools and Materials

You’ll need: a pre-hung door unit (door, frame, hinges), a level (2-foot or 4-foot), a tape measure, a pencil, a drill with drill bits, wood shims (thin wedges), screws (2.5-3 inches long), a hammer, a utility knife, a saw (circular or handsaw, for trimming the door if needed), and a caulk gun with acrylic caulk. Ensure the door unit matches the opening size—measure the rough opening (width, height, depth) before purchasing to avoid gaps.

Step 2: Prepare the Opening

Remove the old door (if replacing) by unscrewing the hinges from the frame and lifting the door out. Take off the old frame if it’s damaged or uneven—use a pry bar to remove nails and trim, being careful not to damage the surrounding wall. Clean the opening, removing debris and old caulk. Check the floor for level: if the floor slopes, mark the highest point, as this will guide shimming to keep the door level.

Step 3: Install the Pre-Hung Door Frame

Lift the pre-hung door unit into the rough opening, ensuring the hinge side of the frame is flush with the wall. Use a level to check if the frame is plumb (vertical) on the hinge side—adjust with wood shims placed between the frame and the wall studs, tapping them gently with a hammer until the level shows no tilt. Secure the hinge side frame to the wall studs using 3-inch screws, driving them through the frame’s pre-drilled holes and into the studs (space screws 12-16 inches apart). Next, check the top of the frame for level—add shims to the top corners if needed—and secure the top frame with screws. Finally, plumb the latch side of the frame, adding shims between the frame and studs to ensure the door closes evenly, and secure with screws.

Step 4: Adjust the Door and Test Operation

Close the door to check for gaps: the door should fit snugly against the frame without rubbing. If the door sticks, adjust the shims—add shims to the hinge side to push the door outward, or to the latch side to pull it inward. Trim excess shims with a utility knife, cutting them flush with the frame. Install the door latch and strike plate: mark the position of the latch on the frame using the door’s edge as a guide, drill a hole for the latch, and attach the strike plate with screws. Test the door again, ensuring it opens and closes smoothly, and the latch engages securely.

Step 5: Finish with Trim and Caulk

Install door trim (casings) around the frame to cover gaps between the frame and wall. Cut trim pieces at 45-degree angles for mitered corners, attach them to the frame with finish nails, and fill nail holes with wood putty. Apply a bead of acrylic caulk along the top of the trim where it meets the wall, and along the bottom of the trim where it meets the floor, smoothing the caulk with a damp finger for a clean finish. Allow the caulk to dry completely (24 hours), then paint or stain the trim to match the door and wall.

By following these steps, you’ll achieve a professional-looking interior door installation that is durable, functional, and aesthetically pleasing. For slab doors, additional steps include attaching hinges to the door and frame (using a hinge template for precision) and routing a hole for the latch—though pre-hung doors are recommended for DIYers due to their simplicity.