In this video, Ask This Old House general contractor Tom Silva is in Salem, MA, to help install a bookshelf that doubles as a door.
1. Remove current door from its hinges by popping up the pins with a hammer and nailset.
2. Remove the old jamb and casing with a pry bar.
3. To level the jamb, place a piece of poplar on the floor and make it level. Set your scribes the overall width of the filler and drag the scribes along the piece of poplar.
4. After marking the poplar, cut it with the circular saw, following the scribe line you traced.
5. Using wood glue, glue the poplar filler piece to the underside of the doorjamb to fill the gap.
6. Repeat the same steps to fill the back side of the jamb.
7. Move the jamb from the door kit into place. Using a 6-foot level, check that it's plumb; if it needs adjusting, place shims between the jamb and the wall studs until the jamb is plumb. Drill through the jamb and shims, and secure with screws.
8. Using a utility knife and a hammer, remove the excess shims on either side.
9. Lift up the bookshelf and place in the pre-fashioned pivot-point pinholes on the top and bottom of the jamb.
10. Glue trim to the jamb and secure with finishing nails.