Digging and Setting Posts
Digging and Setting Perimeter Posts
When digging your post holes be sure to dig at least 3 inches beyond the string line. Some building permits may require 2'x2' post holes while others need only 18"x18". This will depend on your ground, whether you use concrete or not along with other variables like wind and roof weight. You're pole barns posts will normally be set at a 4' depth.
Corner post holes should look like the picture to the right while your on center post holes should have at least 6"-9" of dirt removed from either side of the mark and about 3-4" past the line like the picture to the left.
Use a 6' purlin for the brace in the hole. Slide the ugly end of the post up next to the board, then lift and push the post into place. The 2x4x6' will let the post slide easily into the hole without digging out the sidewall and changing the depth of your hole.
To level the posts, get your four foot level and move the post until it barely touches the string while keeping the bubble in the level in between the lines.
Brace the posts with 2x4's, one end nailed to the post and the other end staked off to the ground when you are pouring concrete. Connect each post to one close to it to assure your posts stay level.
If you are filling the holes with dirt then pack the dirt every six inches to a foot or so to prevent settling and shifting of posts. Pack firmly but not hard, too much pressure on one side of the post can cause it to shift in the opposite direction. You can also use hard packing with the 2x4x6 to move the post back into its position.
Digging and Setting Interior Posts
String up lines using your perimeter posts you set on center. String them across the length and width of the posts. Use the same side of the post for your string line for every post for symmetry and easy digging.