Wood deck posts may be set in concrete or fastened on top of a concrete footing. Since decks are usually attached to the home, codes often require that footings be dug at least below the frost line. Don't forget to call the local dig-right service before drilling holes. This service will contact local utility companies that can note the location of underground services so you can avoid cutting through them.
Holes for Footings or Posts
Check with local building inspectors to determine the frost line in your area. Dig the hole about 6 inches below the frost line.
Widen the bottom of the hole with manual posthole diggers to provide a better hold for the posts.
Drill holes for the posts using a rented power auger. Wear gloves, safety glasses and heavy boots to avoid injury. The auger won't remove large rocks, so you may need to use a pry bar to dislodge them. Drill all the holes before setting any posts.
Setting Posts in Concrete
Pour about 6 inches of gravel into the hole to help with drainage. Drop a post into the hole and twist it so it can settle into the gravel about an inch, then square the post with the deck layout.
Hammer two stakes into the ground near the post so the stakes and deck post create a right triangle.
Attach a post level and determine whether the post is plumb in both directions. When it is, clamp a length of scrap wood to the post on one end and to a stake on the other. Clamp another length of scrap wood to the other stake and to the post. Adjust the bracing as needed so the post is plumb.
Mix enough concrete to fill the hole. The amount needed will depend on how deep you had to drill the hole to get past the frost line. Repeat for each deck post and remove the temporary bracing and stakes after the concrete cures.
Setting Posts on Top of Footings
Mix enough concrete to completely fill the hole. Screed the concrete level with the ground before it hardens. (Screed means adding a finish layer.) Instead of inserting a post, this method creates a footing. Repeat for each post.
Allow the concrete to cure, then attach a concrete anchor to each footing. Mark the location of bolts using the anchors as guides. Drill holes using a hammer drill and a masonry bit. The hammer drill has a dual action that saves wear and tear on the bit and makes a cleaner pilot hole.
Drive concrete screws through the mounting holes on the concrete anchor and into the footing.
Mount posts into each anchor, pull the flaps up around the bottom of the post and screw them in place.