Replace Windows With a Door

You might not consider installing a patio door to be a DIY project. The prospect of opening up a hole (even temporarily) in the side of your house should incite some sense of caution. But in many situations, this is a project that a homeowner can confidently attempt and successfully complete in a weekend.

The key factor that separates an “entry-level” patio-door installation from one that requires more experience or a contractor to complete is the amount of structural or rough framing that must be modified. In general, the less framing that you have to change, the easier the installation. For example, the most manageable installation is simply replacing an old patio door with a new one.


Replacing this set of double-hung windows with a sliding patio door created a new connection between the inside and outside spaces of my house. In addition, the improved view and additional light that the new door provides have transformed the room, making it a much more pleasant and popular place to spend time.

Typically, all you have to do is order one that is the same size, remove the old door and follow the manufacturer’s instructions.

Replacing a set of windows with a door is more challenging, but not much. As long as the windows are framed in a rough opening that is tall and wide enough to accommodate a door, the only added work is removing the framing under the window. The same installation techniques apply whether you are replacing a single window with a single swinging patio door, a pair of windows with a sliding patio door or a larger set of windows with a set of in-swing French doors that feature a third panel of fixed glass on one side.

Will a door fit?
The first step in replacing a window with a door is to determine whether a door will fit within the existing framing. Measure the window rough-opening width and the distance from the bottom of the window header to the subfloor (see ”Key Measurements,” in PDF below). The headers for a home’s windows and doors often line up, so there’s a good chance that the header will be high enough for your new door.

Measuring and determining the correct door size is second nature for an experienced contractor, but for the rest of us, deciphering the size charts in most window and door catalogs can be like cracking a secret code. The best way to ensure that you get the right door is to take your measurements to the store and let the retailer help you determine the specific size that you need.

If the existing rough opening is more than an inch taller or wider than the recommended rough-opening dimensions for a standard door, you will have to modify the opening size or combine the door with other door components to fit the opening. You can add framing under the header or to the studs to make the opening fit a standard-size door and then cover any exposed framing around the door with wider trim or drywall on the inside and with siding on the outside.

In cases where the opening has a lot of extra height or width (at least 16 in. in either direction), you can install a transom window over the door or a sidelight next to the door to fill the extra space.

What's in the way?
Fixtures and utilities such as electrical lines and ductwork that are located inside the wall under the window must be removed or relocated to make room for the door. You also don’t want a heating and cooling vent in the floor to be in the path of the new door.

Visible fixtures are easy to identify, but you must also know what’s inside the wall. If you’re not sure, cut small holes between the studs to investigate. You’ll have to decide whether moving each obstacle is an easy fix or a major challenge that is not worth undertaking.

TIP: Consider hiring a specialized contractor to relocate utilities. Once the space under the window is clear, you can complete the rest of the door installation yourself.

Prep the opening
Once you’ve determined how to deal with any mechanical obstructions, you’re ready to order the door and apply for a permit from your local building-code authority. The next step is to remove the old windows and wall under the window (see “Converting the Rough Opening,” below). To minimize the amount of dust that spreads into house, hang plastic from floor to ceiling around the window and leave the window in place until after you’ve cut the exterior siding; you’ll cut the interior wall after you’ve removed the window.

Many homes built in the past 30 years do not have exterior window casing, and the siding butts up against the window frame. In these cases you have two choices. You can remove the siding on the sides and under the window and then recut and install the siding after the installation is complete, or you can cut back a few inches of siding on the sides and above the window and install new casing boards to fill the gap after the installation. Removing the siding exposes some of the sheathing around the rough opening, making it easier to remove the old window (especially if it was secured with a nailing fin) and allowing you to fasten the new door’s nailing fin and properly seal around the door.

After you’ve removed the window and wall, prepare the new rough opening. Install additional framing as necessary to modify the rough opening size and make the opening plumb and square. Finish the opening by applying flashing to the sill and sides of the framing.

Converting the rough opening


The first step in removing my windows and the wall below them was to determine where to cut the exterior stucco siding. We started by cutting a hole in the interior wall under the window to expose the bottom plate. Then we measured the distance from the top of the windowsill to the top of the bottom plate (photo 1) and transferred that measurement onto the siding (photo 2). Finally, we added the thickness of the bottom plate and the thickness of the sill-support nosing (a sill extension piece required to support the front edge of the manufactured doorsill) to determine where the bottom cut would be.


After closing the windows to prevent dust from entering the house, we used an abrasive cutting wheel and angle grinder to cut through the stucco (photo 3). The width of the opening did not change, so the side cuts were in line with the outside of the exterior window trim.


The horizontal bottom cut was just below where we intended to install the sill support. We pried the cut stucco siding off of the wall. Then we cut the nails that secured the windows in the opening and carefully removed the windows (photo 4).


Next, we cut through the exterior sheathing, framing and interior finished-wall material, following the vertical sides of the window opening down to the floor. Then we pried out the wall below the window opening (photo 5).


To create the correct size of rough opening, we installed a 2x4 on each side. We applied adhesive flashing, starting with the bottom piece that covers the sill (subfloor) and extends 6 in. up each side. Then we installed the required sill-support nosing (photo 6).

Install the door
Most door manufacturers include very specific, detailed instructions for a new-construction installation. The steps are very similar for a retrofit installation (see “Installation Overview," below). In addition to the instructions, many manufacturers also feature additional support information on their Web sites. Carefully follow the manufacturer’s instructions for installing and sealing the door.

The final steps are to fill the interior gaps with insulation and attach the interior and exterior trim. Low-expansion spray-foam insulation works best to fill gaps without putting pressure on the door frame.

Installation overview
First we had to test the fit of the door. We installed it without adhesive, checking to be sure the nailing fins overlapped the top and side framing and that the door fully seated in the opening.


Then we removed the door and applied silicone adhesive across the top of the sill and on the sheathing around the perimeter of the rough opening. We tilted the door into the opening (photo 1), being careful not to slide the door and push out the adhesive under the door.


Next, we used shims to center and adjust the door so it was plumb and square. We secured the door by driving nails through the nailing fins (photo 2) and screws through the manufacturer’s pilot holes in the frame.

My house is clad with stucco siding, and the doors and windows are trimmed with brick edge. I had only about a 1-1/2-in. gap to work with between the edge of the stucco and the door frame. Because I intended to use the same trim, I didn’t want to cut back the siding. Instead, I carefully tucked flexible adhesive flashing under the stucco, covering the entire nailing fin. I finished the exterior by attaching brick mold.

In most cases a rigid drip cap must be installed above any trim that extends beyond the siding plane. I didn’t install a drip cap because the door is protected under a deep (30-in.) soffit that is just above the door. The base of the door barely gets wet when it rains

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above the door. The base of the door barely gets wet when it rains. Once the exterior work was complete, we filled the interior gaps between the door frame and the rough opening framing with insulation (photo 3). Then we finished the interior to match the rest of the room’s trim.

Looking back to the day my friend inspired me to replace two windows with a sliding patio door, I’m amazed at how this simple switch has improved the way we use our home. Now I can’t imagine the house without that door. And I can’t figure out why I didn’t think of the project myself.