How To Install a Prehung Exterior Door

Installing a new exterior door can dramatically improve your home’s curb appeal and energy efficiency. While requiring some skill, this project is within the scope of most DIYers.

In this guide and the video above, This Old House general contractor Tom Silva will show you how to upgrade a prehung exterior door, from removing the old door to securing and weatherproofing the new one.

Preparing for Exterior Door Installation

This project involves replacing an existing exterior door with a new prehung door, meaning a door that already includes a jamb and hardware. It doesn’t require specialty tools, though, in the video, Silva needed a hammer drill to drive screws into masonry.

Tools and Materials Needed

First things first—gather the following tools and materials:

• Caulk gun
• Combination countersink drill bit
• Drill/driver
• Flat pry bar
• Hammer
• Hammer drill
• Ladder
• Level
• Low-expansion foam insulation
• Masonry bit (3/16-inch)
• Prehung exterior door
• Screws
• Shims
• Socket and hex-shank adapter
• Spade bit (1/2-inch)
• Utility knife
• Z-flashing

Measuring and Purchasing

Before purchasing your new prehung door, carefully measure the existing door opening. Measure the width at the frame’s top, middle, and bottom, as well as the height on both sides and in the center. Use the smallest measurements to ensure a proper fit. 

When buying the new door, choose one slightly smaller than the rough opening to allow for adjustments during installation. As you can see in the video, you’ll use shims to ensure a proper fit.

Removing the Old Door

The first step in the installation process is removing the existing door. Here’s how to do it:

1. Remove the hinge pins and take the door off the frame.
2. Unscrew or pry off any interior trim.
3. Remove any screws or nails holding the old frame in place.
4. Carefully pry the old frame out of the opening.

Installing the New Prehung Exterior Door

With the old door removed, you’re ready to install the new prehung unit. Follow the step-by-step process outlined below.

Step 1: Preparing the Opening

Before setting the new door in place, prepare the opening by doing the following:

1. Clean the opening thoroughly, removing any debris or old caulk.
2. Check that the subsill is level and adjust if necessary.
3. Install a drip cap or Z-flashing above the opening. The top leg should slide up behind the house wrap or tar paper behind the siding.
4. Apply a bead of high-quality exterior caulk along the exposed framing where the new door’s exterior trim will meet the wall and across the floor where the door’s threshold will sit.

Step 2: Setting the Door in Place

With the opening prepared, it’s time to set the new door in place. This step often requires an extra set of hands. Here’s how to do it:

1. With a helper, lift the new door unit (i.e., the door and jamb together) and tilt it into the opening, top first.
2. Slide the exterior molding up beneath the Z-flashing.
3. Press the unit firmly into place, ensuring it beds tightly in the caulk.

Step 3: Leveling and Shimming

Proper leveling and shimming are crucial for the door to operate correctly. Follow these steps:

1. Use a level to check the threshold. If it’s not level, use shims underneath to adjust.
2. Temporarily secure the unit with a screw near the top of the jamb’s hinge side.
3. Check that the gaps between the door and its frame are even. If necessary, use shims behind the hinges.
4. Shim the lock side of the frame, adjusting until the gap between the door and jamb is consistent.

Step 4: Fastening the Frame

Properly fastening the frame is crucial for the door’s long-term stability and operation. If you need to drill into masonry, you can rent a hammer drill for the task. Here’s how to fasten your door frame:

1. Remove the weatherstripping temporarily to access the pre-drilled screw holes in the jamb.
2. Drive screws through the jamb into the framing, being careful not to over-tighten and distort the frame.
3. If fastening into masonry, use a hammer drill with a masonry bit to create pilot holes, then use masonry screws.

Step 5: Insulating and Sealing

Proper insulation and sealing greatly improve energy efficiency and prevent drafts, keeping your home more comfortable. Do the following to insulate and seal your new door:

1. Use low-expansion foam insulation to fill gaps between the frame and rough opening.
2. Allow the foam to cure, then trim any excess with a utility knife.
3. Replace the weatherstripping.
4. Apply exterior-grade caulk around the outside of the door frame where it meets the siding.

Step 6: Installing Hardware

Finally, install the hardware on your prehung door with these steps:

1. Install the lockset according to the manufacturer’s instructions.
2. Attach the strike plate to the door frame.
3. Install any additional hardware, such as a door sweep or storm door.
4. Check that the door opens smoothly and the lock engages properly. Make any necessary adjustments.

Maintenance Tips for Exterior Door Longevity

Regular maintenance keeps your new exterior door looking great and operating efficiently. We strongly recommend performing the following maintenance tasks on your door:

• Annual inspection: Check the door and its components yearly for signs of wear or damage. Address any issues promptly to prevent further deterioration.
• Re-caulking and re-painting: Over time, caulk can crack, and paint can chip. Reapply caulk around the door frame and touch up the paint as needed to maintain weatherproofing and aesthetic appeal.
• Regular cleaning: Clean the door surface and hardware regularly to remove dirt and grime. This helps maintain the door’s appearance and the hardware’s functionality.

Addressing Common Issues

Even with proper maintenance, you might encounter some of these issues as your exterior door ages:

• Drafts: If you feel drafts, inspect the weatherstripping and replace it if it’s worn out. Ensure caulking is intact.
• Squeaky hinges: Lubricate hinges with a silicone-based spray to eliminate squeaks. This should be part of your regular maintenance routine.
• Sticking doors: If your door sticks, it may be due to humidity changes or settling. Adjust the hinges or plane the door edges for a better fit.

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