How Far Apart Should Deck Joists And Posts Be?

Are you working on a DIY deck project, and do you want to know the correct distance between joists and posts on your deck? You’ve come to the right place, for we have researched this question, and we have the answer for you.

It is important to consult your local building code if there is a distance requirement for joists and posts for decks in your area. If there is none, you can use the standard distance of joists for decks that should never exceed 16 inches.

Deck posts, on the other hand, should be between six to eight feet apart, depending on the size of the post that you plan to use.

Let’s talk more about the specifics of these distances in the succeeding sections. Learn about how to build a ground-level deck in the sections below.

Read on!

Parts of deck with labeled materials and location diagram outline concept. Educational description for wooden terrace floor with concrete footing, decking, ledger, joist and rail vector illustration. - How Far Apart Should Deck Joists And Posts Be

Why is joist spacing so important?

Because a deck doesn’t have a foundation, its stability is highly dependent on the strength of its frame.

If the floor joists of your deck frame are too far apart from each other, then the floorboards will eventually sag. On the other hand, if the distance of the joists is too small, then your material cost will be too high because you will need too many wooden boards to complete the framing. In the case of our second example, your deck frame will also be less environmentally friendly.

Moreover, less space between the joists will make it harder to install hangers and blocking.

Blocking is lateral support that keeps your joists stable, preventing them from wobbling with weight on the deck surface. Hangers, on the other hand, are metal anchors that keep the joists in place.

Additionally, the joists should be horizontally level with each other. If the joists are not level, then the floorboards will not be even too.

What is the ideal distance between floor joists in a deck?

Patio construction building new above ground deck,

If there are no building code requirements in your area for joists, the standard is a maximum of 16 inches for standard floorboard placement. Diagonal floorboards will need joists with a maximum distance of 12 inches.

These distances should be measured “on center.”

On center means that you should measure the perpendicular distance from the center of both joists. To make it simpler, you can measure from the leftmost side of the first joist to the leftmost side of the second joist. You can also measure from the rightmost side of the first to the rightmost side of the second joist.

One factor that affects the ideal distance between floor joists is the span of the joists.

Is there an ideal span for joists?

A joist span is a distance that the joist will bridge from one end to another. It is typically the unbroken length of the joist.

Horizontal supports, like joists, weaken as they get longer. This is because the longer they get, the heavier they become. Thus, you need to place a limit on the length of the joists because it will start to have a diminishing return.

Longer joists will become heavy enough that they will have to support their own weights in addition to the load on your deck. There is no standard to the ideal span of a joist. This is dependent on the type of wood or material you will use as a joist and the size of the joist.

Find out the maximum length that you can have for the type of wood (or material if you’re not going to use wood) that you’ll be using as joists. Once you exceed that length even by a single inch, you’d have to switch the distance between joists from 16 inches to 12 inches.

Another factor that comes into play is the size of the joist. Joists with greater width and height will be able to go to a greater distance before they start to experience diminishing support strength.

Alternatively, check your local building code for the maximum span that you can have per material that you will use and the size of that material.

What is the ideal distance between posts in a deck?

Residential Backyard Gray Composite Deck

There are two sizes of posts that are common in decks—4x4 and 6x6 posts. 4x4 posts should have a six-foot maximum distance between them. On the other hand, 6x6 posts should have an eight-foot maximum distance.

How to build a deck?

Building a deck is a great way to extend the living area of your house. A well-built deck is a great place to relax and enjoy the company of friends and loved ones.

The good news about decks is that they are simple enough to be a doable DIY project. With the right tools, you can even complete one as a solo DIY.

Fortunately, we have the steps for building a ground-level deck right here for you.

Creating A Layout Of Your Deck

If your area has building code requirements for decks, integrate them into the steps below.

  1. Insert a wooden stake on the ground next to the wall of the house. This should represent one of the corners of your deck.
  2. Place two stakes away from the house, opposite the first one, and place a piece of wood that horizontally bridges the two stakes.
  3. Tie a string across the first string and the opposite pair of stakes.
  4. Check the level of the string. It should have a slight incline going away from the house.
  5. Repeat Steps 1 to 4 on the other side of the deck.
  6. Place two pairs of stakes that will support the string that will go perpendicularly across the first two strings that you have.
  7. Adjust the strings across the horizontal piece of wood until you have a perfect square on all corners.
    • If you have a different shape in mind, adjust the position of the strings and the position of the stakes to match the shape that you want.

Installing The Ledger

Installing deck patio construction. boards with above ground deck

  1. Mark where the ledger board will be on the outer wall with a straight line. Adjust for the thickness of the floorboards and the joists. Ledger boards are horizontal beams installed on the external side of an existing wall. It is part of the deck frame.
  2. Remove the siding and trim from the bottom up to a foot above the ledger.
  3. Cover the area with a waterproof membrane.
  4. Install spacers along the line every two feet in length. The spacer should be two inches wide and an inch and a half thick.
  5. Install the ledger board, aligning its top with the top of the spacers.
    • If you need to combine two ledgers, make sure that ledger board joints fall on a spacer.
  1. Drill a pilot hole through the ledger board and the rim joist of the house at each spacer location.
  2. Install a lag screw into each of the pilot holes.
  3. Install a waterproof membrane that starts from the wall of the house above the ledger and goes down the side of the ledger.
  4. Place a metal flashing over the waterproof membrane.
    • The waterproof membrane and the metal flashing should cover the entire length of the ledger.

Making The Concrete Footer

  1. Mark the locations where you will install your posts. Measure the distance between each location based on the size of the post that you plan to use.
  2. Mark each location. You can use flags, spray paint, or other methods to mark these locations.
  3. Start digging the holes for the posts. The hole should be deep enough to go beyond the frost line and wide enough to support the concrete forms.
  4. Install the footing and pier forms inside the holes.
  5. Use a string to make sure that the forms are level. Trim any excess forms.
  6. Backfill the surrounding area of the forms with soil, maintaining the form’s position.
  7. Fill the forms with concrete. Use a long piece of wood or metal to remove air bubbles as you pour concrete. The top should be slightly convex to drive water away from the concrete.
  8. Insert the post anchor into the concrete, aligning it with the layout strings.
  9. Let the concrete set for a week.

Eapele Post Base is available on Amazon through this link.

Preparing The Bottom Of The Deck

  1. Cover the area under the deck with landscaping fabric.
  2. Cover the landscaping fabric with a layer of gravel.

Installing The Posts

Decking above storage area with wheelbarrow and tools, View of under house, below decking with no privacy screen

  1. Install the post base over the concrete footers. Make sure that it aligns with your string markers and make sure that it is square.
  2. Install the support posts on top of the concrete footers.

Installing The Beams, Joists, And Deck Board

  1. Install the support beams.
  2. Install the joists over the support beams using joist fasteners.
  3. Use joist hangers to install the rim joists.
  4. Screw the deck boards into place. Leave a small space between the deck boards to allow for expansion and drainage.
  5. Install a skirt around the deck.
    • If your deck is not too high, you don’t have to install railings, but you still can if you want to.


The exact distance between joists and posts depends on the size of the joists and posts. Moreover, the material that you will use will also affect the distance between joists and posts.

If you enjoyed reading this article, you might find the articles below equally enjoyable to read:

Deck Shakes When Walked On – What To Do?

Water Leak Where Deck Meets House – What To Do?

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