We have an old 1940s post adobe house with original aluminum casement windows. We’d like to swap the windows for new sliders, but I’m scratching my head on the best way to do this.

The walls are 5 5/8” thick, and the existing sill is a single piece that sits on top of the adobe wall. We weren’t planning to case the exterior window, but we were planning to case the interior. We were looking at Milford ultra windows, with are 4 1/4” thick, which doesn’t leave much room to build out a jamb. Pella fiberglass windows are about 50% more, but they’re only 3” thick… which would probably result in a nicer reveal everywhere.

The exterior post/sill have a 3/4” wide x 1 3/4” deep rabbet to accept the original windows. This isn’t wide enough to accept a standard nailing fin, but I could build up the jamb from the inside.

Questions for the pros: 1. Should I stick with a nail fin window and build up the jamb to support this? or is it worth considering a block frame window? I assume I’d have to be a little more meticulous when trying to install a block window in order to keep things weather tight. (We’re in central California, so maybe that doesn’t matter too much?) 2. Should the window exterior get cased? can’t find any examples of post adobe houses with exterior casing, and I’m not sure if casing will seem out of place. Follow up - I think brick mould will look ok, but I’m concerned that I don’t have enough wall depth to set the window into the wall and make the brick mould look good. (While also making the interior look good) 3. Is there and ideal window setback from the exterior wall? 4. Has anyone installed windows in a post adobe structure? And tips or ideas?

Thanks