How To Replace a Door With a Window

Turning a doorway into a window can dramatically change the look and feel of a room. This project requires moderate carpentry skills but can be completed in a day or two with the right tools. In this guide, we’ll walk you through the process of replacing a door with a window, from removing the existing door to installing the new window and finishing the surrounding area. This Old House general contractor Tom Silva demonstrates the proper techniques for installing a new window into an oversized doorway opening in the video above.

Replace Door With Window: Permitting and Structural Considerations

Before beginning your project, you’ll need to take care of the following:

• Load-bearing walls: Determine if the wall where the doorway is located is load-bearing. A load-bearing wall supports the structure above, such as the roof or upper floors. If it is load-bearing, you’ll need to install a header (a horizontal beam) above the new window to distribute the load properly. Consult a structural engineer or a contractor for this assessment.
• Framing adjustments: The doorway’s framing will likely need to be adjusted to accommodate the window size. This typically involves adding a sill, jack studs, and potentially modifying the existing header.
• Permits and inspections: Depending on your location, you may need a building permit to undertake this project. Check with your local building authority to determine the requirements and ensure that the work complies with local building codes. Inspections may also be necessary to verify that the work is done correctly and safely.

Tools and Materials Needed To Replace a Door With a Window

You’ll need the following tools and materials for the project:

• 1/2-inch moisture-resistant plywood
• 2-by-6 lumber
• Caulk gun
• Circular saw
• Cordless framing nailer
• Drill/driver
• Flat pry bar
• Insulation
• Level
• Minimal-expanding foam insulation
• Roofing nails
• Self-adhesive flashing
• Staple gun
• Table saw
• Tarpaper
• Utility knife
• Vapor barrier
• Window (sized to fit the opening)

You should also wear proper safety gear, such as protective goggles and footwear.

Measuring and Planning To Replace a Door

Take your time to get accurate and precise measurements for your door-to-window conversion. Measure the existing doorway’s width and height, including the frame. Choose a window that fits within these dimensions, leaving room for framing and insulation. Think about the window style that best suits your needs and complements your home’s architecture.

Removing the Existing Door

The first step in replacing a door with a window is to remove the existing door and frame. This process requires care to avoid damaging the surrounding wall and floor.

Removing the Door

Remove any hardware from the door, such as knobs and hinges. Lift the door off its hinges and set it aside. Use a pry bar to carefully remove the door frame, starting with the trim pieces.

Preparing the Opening

Once the door and frame are removed, you’ll need to prepare the opening for the new window. Inspect the rough opening for any rot and damage and repair as necessary. Remove any nails or screws left in the framing, and clean the opening thoroughly to ensure a smooth surface for the new construction.

Framing the New Opening

With the door removed, you’ll need to frame the opening to accommodate the new window. 

Building the Short Wall

Silva demonstrates in the video how to construct a short wall to span the opening below the window. Here are the key steps:

1. Cut a 2-by-6 bottom plate to fit the width of the opening, using a table saw to create a rabbet cut if necessary to fit over existing flooring.
2. Fasten the bottom plate across the bottom of the opening with 3 1/2-inch nails.
3. Cut four 2-by-6 cripple studs to length and nail them to the jack studs and bottom plate.
4. Install a double 2-by-6 sill plate on top of the cripple studs to provide support for the window.

Installing Sheathing and Flashing

To ensure proper moisture protection, cover the outside of the wall frame with 1/2-inch, moisture-resistant plywood. Apply 4-inch-wide self-adhesive flashing around the perimeter of the plywood sheathing. Then, install tarpaper on the vertical sides of the window opening, overlapping the flashing on the plywood sheathing.

Installing the New Window

With the framing complete, you’re ready to install the new window. This process requires precision to ensure a weathertight seal and proper operation.

Before setting the window in place, apply a thick bead of adhesive caulk along the front of the window’s upper nailing flange. Run caulk along the exterior sides and bottom of the window opening.

Set the window into the opening, sliding the upper nailing flange underneath the existing siding. Center the window in the opening and check for plumb using a level. If necessary, use a pry bar to adjust the window until it’s perfectly plumb. Secure the window by nailing through the slots in the nailing flange, spacing nails about 6 inches apart.

Replace a Door With a Window: Insulating and Finishing

Proper insulation and finishing make a big difference in both energy efficiency and the final look.

Insulating Around the Window

To ensure the window is energy-efficient, use minimal-expanding foam insulation to fill the gap between the window and wall framing. Install fiberglass insulation between the cripple studs below the window. Staple a vapor barrier over the insulation.

Interior and Exterior Finishing

Complete the interior look, install drywall around the new window opening. Cut and install casing around the inside of the window to match your existing trim.

To complete the exterior, install new siding over the exposed nailing flanges and plywood sheathing. Caulk around the window to ensure a weathertight seal. Paint or finish the exterior to match your home’s existing look.

Benefits of a Professional Window Installation

While this guide provides an overview of how to replace a door with a window, hiring a professional can offer several benefits. Professionals bring expertise, tools, and efficiency to the project, potentially saving time and avoiding common pitfalls. They also ensure that the job meets local building codes and standards. Investing in professional help may be especially valuable for those lacking experience or time.

Energy efficiency and avoiding damage to your home should be your main priorities. We recommend hiring a professional if you’re not completely confident in your skills, even if it means a higher investment. The window’s energy efficiency may actually save you money in the long run.