How to Replace an Exterior Prehung Door

Having selected and ordered the new exterior prehung door and purchased tools and the necessary materials, you are ready to remove the existing door.

1. Use a utility knife to cut a line in the 90° corner between the interior door casing and wall. This separates the paint and helps to ensure a clean removal of the door casing from the wall.

2. Using a pry bar, gently remove the door casing from the wall. Repeat for any exterior trim (brick mould).

3. Unscrew door hinges and remove the existing door slab from the door frame.

4. Using a pry bar, separate the door frame from the rough opening lumber and remove it from the opening.

Most prehung doors, interior or exterior, are installed in a very similar manner. Exterior prehung doors, unlike interior doors, will come with a set of installation instructions. Be sure to read and follow those installation instructions. Failure to do so will result in voiding the manufacturer's warranty on your new door. (Refer to How to Replace a Prehung Interior Door for help with installation of your exterior prehung door.)

Installing an Exterior Prehung Door

Unlike an interior door, exterior doors need to stand up to the outdoor elements and be weather tight. Prior to installing the new door you need to prepare the rough opening.

1. Ensure that the floor under the door threshold is the correct height. This can be raised, if necessary, by using treated wood materials cut to size.

2. The top and bottom corners and the sill of the rough opening should be shielded from moisture with building paper or self-adhering waterproof membrane.

3. Drip edge flashing, slid between the exterior finish and weather barrier, should be long enough to extend over the top of any exterior trim and cut to fit the width of the opening.

4. After positioning the door in place and securing it, install the exterior door lockset. (For installation directions refer to the manufacturer's instructions and How to Replace a Prehung Interior Door.)

5. On the interior of the door, cut back shims, fill voids between the door frame and rough opening framing with low expansion foam or fiberglass insulation, and install interior door casing.

6. On the exterior of the door you should run a bead of silicone caulk around the door frame, under the threshold, and between all joints or adjacent material transitions. Depending on the width of the exterior gaps, you may need to insert a caulk backer in the gaps, prior to running a bead of caulk. This will seal the gaps on the exterior of your home and prevent moisture intrusion.