Tom,
SIPS are not shown, and would fill the gaps you see between the porches and the main frame. Often in cold climates you DON'T want timbers penetrating the insulating envelope.
If you see gaps below the posts (by the way, posts are vertical and beams are horizontal, rather than vice-versa) it's either because they rest on concrete foundation or there is a flooring layer not shown. Joinery on the post feet, such as stub tenons, is also not shown.