When constructing a deck, the shoes that support the posts and beams must be spaced and sized accordingly. To determine the space between the bases of the platform, you need to consider the size of the base and beam, as well as the span of the beam. Generally, posts should not be more than 8 feet apart, although some builders place them every 4 feet for a more rigid frame. The maximum spans can reach up to 15 feet.
To start, mark the location of each post on the platform to locate the mounting position. There is no minimum interval, but it is recommended that you use one beam along the outer edge of the platform (a ledger bolted to the house supports the other end). The beams are allowed to cantilever past the end posts to one-quarter of the beam span between the posts. This allows you to make the beam a little smaller.
The dimensions of the span of the beam and cantilever are taken from the center of the posts, not from their faces. When sizing beams, it is best to first determine the spacing between them and then use an appropriate joist size for that spacing. If your platform will not be more than 6 feet from the ground, it is recommended that you space your support beams no more than 12 feet apart. You can also slightly reduce this space by placing a cantilever beam.
If you cannot find your local building code online or if you just want to experiment with calculations to see what your deck's support posts would look like, you can use an online deck post spacing calculator. Joists that are longer will require platform support posts that are more spaced from each other, so a larger platform span means that you'll have to space your deck support posts closer together. The local building code will provide roof construction tables that indicate allowed spacing between roof support posts and will also tell you at what height you can build a deck with 4 × 4 support posts. Online calculators are great for visualizing what your deck might look like in terms of where you would place its support posts, but keep in mind that they are just estimates.
To get an accurate result, transfer the shape and dimensions of your platform plane at scale to your full-size construction area. Alternatively, you can always make a larger platform beam and separate your support posts further apart. When building a deck, it is important to consider how much space should be left between posts and beams. The size of the base and beam, as well as the span of the beam must be taken into account when determining how far apart each post should be placed.
Additionally, it is recommended that one beam is used along the outer edge of the platform with a cantilever past end posts up to one-quarter of its span between them. When sizing beams, it is best to first determine their spacing and then use an appropriate joist size for that spacing. If your platform will not be more than 6 feet from ground level, it is recommended that support beams are spaced no more than 12 feet apart. If you cannot find your local building code online or if you want to experiment with calculations for your deck's support posts, an online deck post spacing calculator can be used.
However, these are just estimates and an accurate result can only be obtained by transferring shape and dimensions of your platform plane at scale to your full-size construction area. Alternatively, making a larger platform beam and separating support posts further apart may also be considered.