Plywood stiffener. A great way to reinforce the split-stud wall is to install a ripped piece of 3/4-inch plywood between the studs.
First, fasten the top of the plywood to the header frame (23). Then drill 1/8-inch pilot holes through split-stud slots and fasten the split studs to the plywood with 2 1/2-inch screws.
It's a good idea to position these holes near the top or the bottom of the slot, so as to leave as much room as possible for fastening the split jamb to the split stud later. When using a plywood stiffener, I install the second (midspan) split-stud pair after the plywood is attached to the first split stud; I secure the second split stud to the header, then to the plywood, then to the floor.
Hanging the Door
Cut the bottom of the door to clear carpet or other flooring. To measure the necessary door height, install the carriages in the track, suspend a carriage hanger from one carriage, then measure from the bottom of the hanger to the floor. Subtract for carpet or other finish flooring, plus allow at least 1/4-inch clearance.
This is one case where cutting a little too much off the door is better than not cutting enough: If you don't cut enough, you may have to remove the door after all the trim is painted. We've all had to do that at least once. What's even worse, though, is if a tile floor is installed, you may not be able to get the door out of the pocket. Don't ask how I know this.
Center the carriage hanger on the door, approximately 3 1/2 inches from the edge. It's best to avoid mounting hanger screws into the end grain of door stiles, but on narrow doors there's little choice. When I'm working with a heavy door and have to install hanger screws into end grain, I mortise out a section of the top stile with a plunge router and a template jig, then glue a solid block of wood into the mortise.
Always predrill pilot holes for every screw you put into a door (26). Fasten the hangers with 1 1/2-inch mounting screws. It helps a lot if on the first try you position the hangers with the bolt slots facing the front of the door. If you haven't done so already, insert the carriages into the track.
Hanging heavy doors alone isn't hard. Start by angling the back of the door into the frame opening, then tip it up on the front edge and slip the rear hanger plate over the carriage-wheel bolt. Slide the door into the pocket a little bit, then raise the front edge of the door and slip the front hanger over the front carriage-wheel bolt. Don't bother adjusting the height of the hangers until the strike jamb is installed.
Installing the Trim
Install the strike jamb, plumb and straight, and fasten it securely to the trimmer. Then adjust the carriage-wheel bolts to align the door parallel with the strike jamb.
I always attach split jambs with screws, locating the screws in the split-jamb legs so they center on the cutouts in the aluminum frames. To position the split jambs properly, use a spacer the same thickness as the drywall or other finish wall material.
Attach the split-jamb heads last. To make life easier for the next guy, I use screws in both jambs, because replacing the door sometimes requires the removal of both of the top split jambs. Remember that the door stop will cover all the screws.
I install the door guide next. Holding the guide near the bottom of the door, I center the door in the pocket opening, then drive a nail partially into the slots on each side of the guide. I adjust the guide up or down while sliding the door in and out of the pocket, checking that the bottom of the door isn't rubbing.
To make sure it's centered, I open and close the door several times; once I'm positive everything is sweet, I stand up and double-check the whole thing one more time, then kneel down and drive two more nails into the holes on each side of the guide plate.
There are several types of door guides available; for custom doors, I prefer a floor-mounted guide. I cut a kerf in the bottom of the door with a router and slot-cutter, wax the kerf with a candle, then mount the guide to the floor, centered in the pocket opening.
I install the door stop using as few 1-inch brad nails as possible. To allow for seasonal movement, as well as for a latch, I make the gap between the door stop and the door about 3/16 inch.
Nail door stop on the legs of the split jambs, too, covering the door-guide plate. I accommodate the thickness of the plate by carving out the back of the door stop slightly. Again, you should use as few nails as possible so the stop can be removed easily if the door ever needs adjustment. And if you can help it, don't caulk the door stop to the split jambs! Also, I don't install stop on the strike jamb unless the client insists; it looks silly and gets scarred every time the door is closed.
Finally, install the rubber bumper on the rear jack stud. If you're not hanging the door before drywall, don't forget to get that bumper in while the cavity is still open. Use a properly sized spacer block to ensure that the front edge of the door is flush with the door stop at the face of the split jambs when the door is fully retracted into the pocket. (Make sure to allow for the thickness of both the split jambs and the stop.)
Now wait for the drywallers to finish the wall, then install the casing. One last note of advice: Use 1 1/4-inch nails to fasten the casing to the pocket wall. Do the same for the baseboard. And don't ask me how I know this.
Gary Katz moderates the JLC Online finish-carpentry forum and is a frequent contributor to JLC.