How To Hang Pre-Hung French Doors

Measure the door opening to ensure you have a correctly sized door. Use a tape measure to measure the width and the height. Add 2 1/2 inches to the height measurement and 2 inches to the width measurement to allow for doorjambs and framing.

Remove the new French door from its packaging. Use box cutters to cut the strips on top of the cardboard surrounding the doors edges. To prevent damage to the door, take care not to cut too deep into the cardboard.

Run a line of caulking in the center of the bottom of the door opening where the threshold is to be installed. Press the tube of the caulk gun on to the floor and apply even pressure on the handle as you move the gun in a straight line across the floor opening.

Set the bottom of the door frame into the opening first. Push the door up into place. Have a helper stand on the other side of the door frame to prevent the door from falling through. Have him hold the door into place during installation.

Install shim pieces under the center of the door frame. Slide the tapered side of the shim under the door frame on the hinge side. Using a hammer, gently tap the shims into place between the bottom of the door frame and the floor. Install shims about every 6 to 8 inches to prevent sagging.

Place a level on top of the door frame at the floor. Adjust the shims if necessary. Hammer the shims on one side or another until the door is level. Measure the gaps at the top and bottom of the door to ensure the door is even in the opening. Install shims on both sides of the door frame.

Hammer three shims on each side of the door. Shim between the wall and the frame. Install one shim in the center of the frame, one in the top third and one in the bottom third. Divide the measurement of the door height by 3 to find the exact distance to leave between each shim.

Tap the shims into place. Hold a level on the side of the frame to ensure the frame is centered in the frame. Adjust the shims as necessary. Install shims on both sides of the door frame.

Insert 3-inch drywall screws into the frame at each of the shims. Install the screws from inside the door frame into the door opening.

Press insulation between the gap in the door frame and the opening to prevent any air from entering.

Nail the door trim into place on both sides of the door. Place a level on the trim to ensure it is level before nailing it into place. Use 2 1/2-inch finishing nails placed 4 to 6 inches apart.

Run a thin line of caulk along the top of the door frame next to the opening to seal the frame.