Perhaps you have a lovely sun-room that requires more access, so you decide to install a pair of bi-fold french doors. It is often the case that a large window may be the only place to install your bi-fold french doors. This way, a minimal amount of wall cutting will need to be done. This is the idea installation method because the window already has a header in place and of course a large cutout already exists.
Assessment and Measurements
You need to look at your current window and figure out how much of the window cutout you can use for your new bi-fold french doors. You will want to measure the height and width. Also measure the window's location on the wall compared to where you will place your door.
You will then need to remove the trim around the window and some of the drywall above it, so you can inspect the header condition and placement. Determine whether or not the header will need to be moved or replaced.
Once you have evaluated the situation with your window, then you can begin demolition work. You will need to remove the window from the opening using the Sawzall and cutting the frame out or by using a screw-gun to remove all the perimeter screws. The window should then be pulled out by one or two people, depending on the size.
You must first find out if the wall your working on is considered a "load bearing" wall, which means that it generally can't be modified unless you use floor jacks as supports. Consult an inspector or contractor to find out more.
If you have to re-frame the opening, you will need to use a hammer or sledgehammer and remove the studs that are in the way. Once all of the necessary studs have been removed, then you may need to work on the header. Is it in the right location? Does it need to be replaced? Perhaps it needs to be re-sized? These are important elements to look at to make sure the header is just right for your new bi-fold french door.
Re-framing the Opening
Now it's time to frame the opening to accept your bi-fold french doors. Use your table saw or skill saw to make any cuts. Make sure you have your Shop Vac plugged in to limit the amount of dust and wear your eye, ear, hand and mouth protection.
Doors require double king studs, which means that two sets of studs are on each side of the door. Your finish measurement with drywall in place should match the standard size of bi-fold french doors that are commonly available. Standard sizes are 60x80, 72x80, or 96x80.
Installing the Bi-fold French Doors
Once the framing and drywall is complete, then it's time to install your bi-fold french doors. You will need to purchase two sets that equal your finished opening height x width. For example, say you have a finished opening size of 72x80, then buy two sets of doors that are 36x80 and install them side by side according to the instructions.
That's it. Converting an existing window into a door opening with bi-fold french doors is something that will take preparation and time to do, but the end result will be fabulous.