Post height should be figured at the planning stage and your plans should include an elevation view of each side of the house, including any gables. This view will show the posts, the heavy timber girt above them (also called the girding beam) and floor joists, if supported from below by the girt. (The alternative is to hang the floor joists on the girt with metal joist hangers made for the purpose.)
If you are building your own house, chances are that you will be designing it yourself as well. Post height can be figured by working back from the desired ceiling height. For example, let’s say that the plan calls for the ceiling joists to hang from the girts with joist hangers, and, further, that the joists are the same depth as the girts, perhaps ten inches. If you want to maintain eight feet to the underside of the ceiling (or exposed floor joists), then the posts will be the same height as the ceiling or underside of exposed joists. If the joists are installed directly above the girts, then you can shorten the posts by the thickness of the girt and still maintain the desired headroom. With an eight-inch thick girt, for example, a seven-foot four-inch post will still give eight feet of headroom to the underside of the joists.
Another way I have figured this, at four different houses now, is to base everything on the doorframe. Let’s say we start with a standard six-foot eight-inch (203 centimeter) door and use an eight-inch-thick girt as the top part of the doorframe. (Six-foot eight inches plus eight inches equals seven-foot four inches, or 224 centimeters.) Further, let’s say that we support the ceiling joists on top of the girt, not with joist hangers. In this example, headroom clearance will be seven foot four inches to the underside of the joists. With exposed eight-inch joists, the visual effect is eight feet (244 centimeters) to the ceiling planks, quite sufficient unless you are very tall. This is the way it is downstairs at Earthwood as well as in the new solar room upstairs (see next chapter) and we like it. The main upstairs area slopes up from about eight feet at the edges to about nine feet at the center.
All of this is a matter of individual taste, but have such details well planned before you order materials.
