Now it’s time to start dealing with the holes you’ll need for your other joists. Once you have determined the diameter and depth simply dig the necessary number of holes, being sure to dig good, straight walls. Be sure to dig until you hit stable undisturbed soil that does not settle, it is not recommended that you backfill a hole with loose dirt before you pour concrete as it may cause settling. This is another area where you will need to check your local codes as most locations require a certain depth for the posts. Failure to use the proper depth could also result in a loss of stability in your deck over time.
Begin mixing your concrete and then pour it into the holes you’ve created (one at a time) allowing an inch or two at the top to allow it to be smoothed out and place your pier blocks (typically recommended that you purchase these ready made). Remember, your pier blocks will serve as the transition support from the posts supporting the girders to the concrete foundation footings. The weight of the deck will keep the post in contact with the pier block though some do come with small pieces of redwood or pressure treated lumber imbedded into the tops to allow the post to be nailed to the blocks.
Now begin building your girder/post system, by cutting your wooden posts to the proper heights (level to the bottom of the joists). It is highly recommended that you pre-build the entire unit before moving it into place. Again, your local code may dictate some of the specifications you will need to use for this system.
Once you have cut all your posts, your girder stock should be cut to the specified length (length of the ledger plus 3″) and again, you should if at all possible, use one piece and if you must use two pieces be sure they meet at a post so that they can both be attached. Girder stock should be as straight as possible, since bowing will cause the deck to rise or fall. If there is a small bow (not more than a half inch per twelve feet) pointing it skyward will allow it to settle properly over time.
Using properly galvanized bolts, assemble posts and girders into a single unit, and drill your holes so that the bolts will all go through the wood very straight. Once you have assembled the entire unit, move it under the two outer joists (making sure they have remained at right angles). Using L Shaped fasteners and galvanized nails, nail the joists into your girders.
Now that you have your girders in place, you’re ready to begin the installation process for the remainder of your joists. The distance between joists depends on the size of your joists, the spacing of your joists, the span from your ledger to your girder, the type of wood that you’re using and load capacity. If you undersize or over space your joists, your deck may collapse. The local building code office will advise you on proper sizing and joists as well as spanning, though typically twenty four inches on center is adequate.