Let’s say you’re looking at building your own deck and you’re not a carpenter, nor do you have much in the way of relevant experience in the matter. Since one of the first parts of actual construction is burying your posts, it stands to reason that spacing is your first concern.
Spacing between your posts should be no more than 8’, however, there are numerous examples of larger spans between posts, depending on the size of the joists and the beams, along with several other factors.
Your posts are a major part of the weight distribution though, so you want to get it right. If this is your first time, then the odds are, you aren’t bringing in giant beams and joists that require a small crane to hold up until they’re properly braced then fastened.
The fact is, your post spacing will largely be determined by the layout of your deck, the size of your beams, and the size of your joists.
Deck Spacing: How Does it Determine Post Spacing?
There are several factors (discussed above) that determine the space between your posts. However, there are also more minimal factors to consider as well. So, to compile them all:
- How large your joists are
- The size of your beams
- Whether or not your deck is attached to the house
- The size of your posts (4×4 or 6×6)
- Deck height
If you’re doing a floating deck, things get even simpler or you may not need posts at all. So much depends on the design and the layout of your deck, which is as it should be.
If you have some experience building decks, then you probably have an idea of where you want to go with everything. If it’s your first time, you may want to consider the simplification benefit of attaching the deck directly to your home.
Attaching the Deck to Your Home
With this kind of design, you get to eliminate some posts (as your home’s foundation will take up this task) and at least one beam.
For example, a small, 8’x12’ deck that’s not attached to your home should have two beams, the accompanying joists, and six, 4×4 posts, with three posts at the top of the rectangle and three at the bottom of the rectangle.
Attaching it to your home means that you get to drop one beam and three posts, as your house, along with what is called a “ledger board” will serve as the top of the rectangle.
Attaching your deck to your home is one of the most common choices amongst new deck builders because it simplifies the process in the extreme.
It’s also much more cost-effective when you consider the skyrocketing costs of wood in the lumber industry as it stands today. If you decide to go with a pretty large deck blueprint, the amount of money that you save if you attach the deck to your home will be extensive.
Deck Height
The higher your posts, the weaker the support structure for your attached beams, in terms of how long your beams can be and, as a result, how far the spacing between your posts.
Floating decks can get really simple with only four posts to support an 8’x12’ deck, so long as it’s so low that your joists are essentially sitting on the ground.
You can get away with that up to 4’ in height, however, you’ll want to increase your post size to 6x6s instead of 4x4s, so that it can adequately support a 12’ beam.
At 5’, you’re looking at adding posts and the potential for a 12’ beam goes away.
The Size of Your Joists and Beams
This one goes without saying because 4×4 posts, no matter how impressive the footing that you pour, can only do so much when you’re using giant beams and only moderately smaller joists.
As a general rule of thumb, when you increase the length of your beam, you should also increase the number of posts. If you want to maximize your post spacing to 8’, then you should add posts if your beam exceeds 8’.
As with your beams, longer joists require more posts to support them. When you think of it from a physics perspective, how long do you want your joists to be, with all of the added weight of deck boards resting on them, without post support?
That’s not to mention all of the stuff that’s going to end up on the deck, like patio furniture, grills, jacuzzi possibly, and the foot traffic of large get-togethers.
The same holds true if you have a ton of joists, rather than fewer but longer joists.
The Size of Your Posts
There is a load of difference between the support structure of a 4×4 and 6×6, especially when you get into the question of height. If you want your deck to sit more than 5’ off the ground, then it’s best to jump up to the 6×6 posts from the 4×4.
Sure, it’s more expensive, however, you may also violate your local building codes if you construct a 6’ high deck on 4×4 posts. The codes aren’t the same everywhere, but they are similar everywhere.
You’re also limited with 4×4 posts in that you can’t use 3-ply beams, as they simply won’t fit on a 4×4 post. If your goal is to build a deck that covers a great deal of real estate, a 3-ply beam will be enormously advantageous.
This is especially true when you consider the fact that you won’t have to dig down and concrete in so many posts because you can increase the distance between posts when using 6x6s on a much larger deck.
Final Thoughts
The most significant rule to remember when building a deck is to space your 4×4 posts no more than 8’ apart and that’s only if your build design is pretty simple, small, and generic.
If you start getting fancy, that’s perfectly fine and good, as fancy can also mean a lot of fun and an impressive deck to show off down the road. However, it also means changes in distances and a lot more money.
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