The sill is a 2x4, beveled on both edges at 15 degrees, sitting on top of a 2x6 apron with a matching bevel and a 3/4-inch-by-3/4-inch rabbet on the bottom to receive the siding.
Once we have the windows on site, we measure and cut all the trim packages, then carefully treat all the raw wood surfaces with a good exterior primer.
Trim pieces after top coats are applied; we do the painting all at once, racking up the pieces to dry, so that the installation can proceed without interruption.
I fasten the head trim with 3 1/4-inch double-dipped galvanized casing nails.
On top I add the secondary cap flashing.
The secondary flashing is sealed to the building paper with flashing tape.
I then nail on the sill; at this point the window is ready for siding installation.
To prevent wicking, the siding gets held off the cap flashing by the height of the end dam.
The 1x4 side trim follows the siding, covering the ends at the butter boards and nearly flushing out with the head trim.