From 
Image 1 of 14
1. Rip narrow strips for the cove, base and casing
using the setup shown. Leave blade guard in place and use the push block to
complete the cut.
Image 2 of 14
2. Plane the cut edges to remove saw marks. Then
plane some of the strips to 1/2 in. thick as needed.
Image 3 of 14
3. Position and predrill the window stool. Then
add glue and nail it to the window frame. Snug the 1x4 apron up under to the
stool and nail it in place.
Image 4 of 14
4. Mark the jambs to allow a 3/16-in. reveal. Cut
side casings about 1/2 in. too long and fit them to the sill. Then mark and cut
the top of the casings and tack them in place.
Image 5 of 14
5. Measure to the outside edges of the side
casings and cut the top casing to this length. Add 1 in. for the cap and fillet
and nail these pieces to the top and bottom of the casing.
Image 6 of 14
6. Center the completed assembly in place over the
side casings. Predrill 5/64-in. holes through the fillet and nail it to the
window frame with 2-in. finish nails. Nail along the top of the 1x4 into the
wall framing with 2-1/2 in. finish nails.
Image 7 of 14
7. Butt the baseboard at inside corners. Adjust
for a tight fit by scribing a line and cutting to it. Nail the 1x4 to the wall
studs, the lower cap to the 1x4 and the cap to the wall.
Image 8 of 14
8. Notch the lower cap to overlap the casing by
1-1/4 in. Cut the notches a little undersized with a handsaw and file and sand
to the lines.
Image 9 of 14
9. Hold outside corner pieces in place, mark and
miter them. Complete the baseboard by cutting the baseshoe and nailing it to
the baseboard.
Image 10 of 14
10. Mark the studs, then butt the 1x4s to the
ceiling and nail them. Butt and scribe inside corners (see Photo 7) and miter
outside corners.
Image 11 of 14
11. Use a pair of 2-ft. long test boards to
establish an accurate miter saw setting. Then cut and fit the ceiling boards
and nail them to the ceiling framing.
Image 12 of 14
12. Along walls without ceiling framing, use
construction adhesive and temporary braces to attach the
boards.
Image 13 of 14
13. Cover gaps by fitting and nailing the 3/4 x
3/4-in. piece and the 1/2 x 1/2-in. edge pieces. Butt the inside corners and
miter outside corners.
Image 14 of 14
14. Draw horizontal marks around the room and add
the plate rail following the details in Figure A. Notch the ends to overlap the
casing as shown.
I would have liked to see some finished photos of the bottom edge corner of the baseboard area, as well as, the completed window.