Confirming Door Jam Dimensions for Thick Walls – GreenBuildingAdvisor

idahobuild,

Just like on interior doors, the jambs and head cover the area from the inside of the trim on both the exterior and interior.

So in your case, as long as you are planning to butt your siding against the exterior door trim you would use what you identified as #2. If however you are mounting the window and door trim on your siding, you would have to account for that in the increased depth required.

If you used what you identify as #1 you would be left with a gap revealing the ends of your drywall you would somehow have to cover.

As A.Goldstein said, it may be easier to get standard jambs and make your own exterior extensions.