It is quite common for the skirt boards (grade boards), girts, and truss carriers to be nailed to the outside perimeter of the foundation posts. This is the easiest, quickest, and cheapest method for barns not finishing the interior of their walls.
Bookshelf girts (also called commerical girts) provides more strength against high wind and provides the substructure to finish out the interior walls of your farm building
, garage, or barn.
This method is simple enough. The 2x6 girts are laid flat between the posts at whatever on center your site location requires, with 2x6 strongback support.
Interior girts are toe-nailed in place with
16D or 20D galvanized ring shank nails being typical hardware.
When girts are bookshelfed, grade board and truss carriers (or girders) are notched into the post. This involves notching the post 1 1/2" to fit the dimensional lumber flush with the post to provide the plane for installing siding. Also, posts are embedded at the exact length and width of the building instead of allowing for 1 1/2" since the measurement is no longer girt to girt (its post to post instead).
Another option is to size the girts 1 1/2" wider than the posts allowing the girt to protrude out parallel with the truss supports and grade board as shown below. This eliminates notching and provides a deeper cavity for insulation and air gap.