Order your doors at least three weeks ahead of installation. You'll need to decide between in-swing (Image 1) and out-swing (Image 2) doors. In this project, we installed in-swing doors.
Be sure to order the new doors based on rough opening size and not on unit size. Because you have to order the doors in advance, you will need to create a rough opening in your walls to accommodate the dimensions of the pre-hung French doors you ordered.
Locate the wall studs by tapping the walls with a light hammer tap, or use a studfinder.
Use a hammer to knock a hole in the wall between each of the studs you're removing, then tear away enough of the wall so you can see inside, checking for electrical wiring and plumbing.
Continue knocking holes in the wall until you can tear off all of the old wallboard. Remove any insulation.
Remove the trim around the old door, as well as any baseboards, chair rails and crown molding within the marked area.
Before continuing, move any electrical switches, wiring or junction boxes. Turn off the main breaker, remove the electrical box, cap the wires, and tuck them up into a rafter or a wall cavity to get them out of the way. Do not forget to place this electrical hardware in a more appropriate place before you finish this project.
Once the wallboards are off on one side of the wall, you can attack the other side of the wall. If it's an interior wall and it's wallboard on the other side, repeat the process you just completed.
If the other side of the wall is an exterior surface, first check outside to make sure you won't cut anything you're not supposed to. On this project the exterior wall is wood. When you're sure that it is safe to cut, make a plunge cut through the wall with the reciprocating saw (Image 1) and a standard bi-metal blade. Make a cut from top to bottom along the studs in each stud cavity.
After cutting through the boards, just push the wall out from one side. Work the boards free as well as any excess pieces nailed directly to the studs. Be careful not to cut any electrical wires or boxes (Image 2).
You will also need to remove drywall from the ceiling area where the new header supports the ceiling rafters. Use a utility knife to score the drywall and use either a keyhole saw or a reciprocating saw to cut away the drywall. You may need to get into the attic space to insure you won't be hitting any electrical wires in the attic.
Remove the old door and its hinges from the old door frame (Image 1).
Use a reciprocating saw with a standard bi-metal blade to cut through the nails holding the old frame in place (Image 2). Remove the door frame.
First, mark the "king" stud (the existing stud from the old doorframe which runs all the way from the bottom plate to the top plate. Do not cut this stud.
Use the reciprocating saw to cut through the other studs that are now standing in the new rough opening, which in this project is 5' 6" wide, including a 1/2" addition on each side to accommodate the insulation and any adjustments to ensure that everything is plumb.
The opening for the new French doors requires a header that spans the opening and carries the weight of the rafters above it. The header is supported on both ends by two shorter studs called "trimmers" or "jack studs" (see illustration), which are placed inside the "king" studs (see image).
A header for a 5' 6" opening can be built out of 2" x 10" lumber with a piece of 1/2" plywood sandwiched between, but such site-constructed headers are considered not as strong as LVL (laminated veneer lumber) beams, which you can purchase at the lumber yard. In his project the contractor is installing two LVL beams side-by-side as a header.
Determine the width of the header. Then measure and cut two "jack studs," which carry the header flush to the ceiling members above. Use 16 penny nails to nail one of the jack studs to the king stud and the other jack stud to its fellow jack stud.
Use a level to check to make sure your framing is plumb.
Measure across the opening to place the other king stud and jack studs (the distance is equal to the length of the header). Nail in a new king stud, top plate-to-bottom plate, on the opposite side, and install two jack studs (as in the previous step) to hold up the other end of the header. Doublecheck your measurements before you nail. Check for plumb.
Set the first header beam on top of the jack studs. Check that it's level, and shim it up if it's not. Nail it into place as shown in the image.
Note: The lambeams that come from lumber yards are often not square because they are cut with a chain saw. To make sure they're square, use a framing square to even the ends.
Set the second header beam in right next to the first one and attach it with nails to the first header. The two header beams together should be the same width as the stud wall.
Once the header beams are in place, use the reciprocating saw to cut through the bottom plate and dig it out with a pry bar or cat's paw.
The safety braces which were installed in the previous step of this project can be removed at this point.
Fish the electrical wiring through the wall to re-route it to the new switch box, out of the way of the new rough opening. Use wire nuts to tie off any loose wires. Never bury an electrical box inside a wall.
The new rough opening is ready for the installation of pre-hung French doors.