Here is a mockup of the windows I will be building. I milled the mockup from spruce 2x4s from the basement.Window exterior
3 trial runs of corner joint. Top was the first draft, bottom is final.
Joint dissassembled. In this finger joint, there are three gluing surfaces. The exterior face is facing down.
Joint assembled. I will drill & insert a peg at each corner joint. Note the channel on the edge of 1/4" thick exterior flange to accept a bead of silicone to seal the glazing in place. There is a saw kerf in the rabbet to accept the glass stop, shown assembled in the next photo.
Glass stop in place. The thickness of the gap for the insulated glass unit is 5/8". Both the exterior flange and the glass stop have a silicone caulking channel.
On each window assembly, there will be a v-seal weather strip to seal out air infiltration and a tube gasket to create a thermal seal.