As a general rule, bolts should be spaced 16 inches apart to support joists up to 12 feet long. Many deck builders prefer to leave a ½ inch gap between the ledger and the wall to allow for water drainage, rather than using joint plugs. When mounting ledgers in existing homes with an interior roof, it can be difficult to separate the ledger from the wall. The code only recognizes transverse bolts for this purpose, so you would need to open the roof to install washers and nuts, and then patch the roof.
However, you can now use patented structural screws if your local construction official accepts engineering letters from manufacturers. The ideal spacing between deck posts is 8 feet or less. This distance depends on the type of wood used, as well as the size of the beam and joist. There is no minimum spacing, and maximum spans can reach up to 15 feet.
To determine the location of each post on the deck, start by marking its perimeter. Generally, posts should not be more than 8 feet apart; some builders even place them every 4 feet for a completely rigid frame. If you can't find your local building code online or want to experiment with different post spacing designs for your deck, use an online deck post spacing calculator. When using a two-layer beam on 4x4 posts, there is a limit to how far apart you can space the support posts of your deck.
To locate the bases of the platform and establish the correct spacing between deck posts at the bottom, use pegs and ropes. There are tables that allow deck builders to determine how far apart they can place support posts based on the size of the beam, joist, and post. The code will also tell you at what height you can build a deck with 4x4 support posts; this height usually does not exceed 5 feet from the ground to the surface of the platform. For most DIY projects, mass tables, masonry lines, tape measures, and simple calculations are enough to determine the spacing between platform bases.
While these online calculators are great for visualizing what your deck might look like in terms of post placement, keep in mind that they are just estimates. Proper spacing between deck posts follows the deck post spacing chart found in local building codes. A larger platform span means that you'll have to space your deck support posts closer together. If you need help determining the distance between platform bases, enter your platform dimensions into a base and beam calculator.
Local building codes will likely provide roof construction tables that indicate allowed spacing between roof support posts. Like a deck beam, joists that are longer will require platform support posts that are more spaced out from each other. This is achieved by transferring the shape and dimensions of the platform plane at scale to the full-size construction area.