Deck Joist Spacing and Span Chart

Joist Spacing For Decks

Planning and building a DIY deck frame is a great way to build a personalized deck you can be proud of. While building a deck frame isn’t as simple as nailing a few boards together, it is an attainable DIY project - with the right knowledge and guidance. That’s where DecksDirect comes in. Check out this guide to plan your deck with the right joist spacing and joist spans for your project.

A look underneath a deck at a line of deck joists, all installed with correct deck joist spacing based on the framing and decking used

Table of Contents:

Why Do I Need To Plan My Deck With The Right Joist Spacing?

It’s essential to plan your joist spans and joist spacing correctly - this makes sure your deck will meet building codes and makes it much quicker and easier to get the building permits you need to get started on your deck project. More important than all that, though: joist spacing and span requirements are based on tried-and-true industry standards, and they’re in place to make sure your deck is safe and structurally sound for you, your family, and your friends.

An in-progress deck frame with joists and beams in place

DecksDirect: Your DIY Deck Project Guide

At DecksDirect, we know you’re capable of planning and building your own deck frame. And we want to give you the tools to make it easier! Here are two resources we provide to help you get started:

DecksDirect’s Deck Framing Guide: To learn more about all the parts and layout of a deck frame, check out our How To Frame A Deck Guide, written by experienced decking professionals.

Personal Deck Planning Guidance: Unlike your local hardware store, we don’t sell you deck parts and send you on your way. We staff a team of experienced deck project planners who are available by phone to help you plan your project from start to finish. Give us a call at 1-888-824-5316 to work with a knowledgeable deck planner to create a deck project perfectly suited to your vision and your experience level with DIY builds.

How To Plan Deck Joist Spacing & Joist Spans

Terms to Know

  • Joist Span: the length of your joist from one end to the other
  • Joist Spacing: the distance between each joist, measured from the center of one joist to the center of the next joist. (This is called on-center spacing).
A diagram showing what deck joist spacing and deck joist span mean

What Is A Deck Joist?

Joists are structural elements that make up the framework of the deck beneath the deck’s walking surface. Joists attach to a ledger board using joist hangers and run the entire length of the deck, perpendicular to the house.

A diagram pointing out the deck joist, deck beam, and support post, among other parts of a deck frame

Deck joists, like the rest of your deck’s frame, can be made from a few different materials. Traditionally, deck frames were built with pressure-treated lumber. But new steel framing options are becoming more and more popular for their strength and durability. Steel framing also supports longer maximum joist spans, and steel framing parts are more consistent in size and straightness, making things much easier for DIY builders.

How Far Apart Should You Space Deck Joists?

The short answer: deck joists are typically spaced either 12 inches or 16 inches apart, on center. (On-center means the length from the center of one joist to the center of the next joist, rather than a gap from edge to edge). 

A slightly more in-depth look: the maximum joist spacing you can use for your frame will depend on a few factors:

  • The size of your deck joists
  • Your framing material
  • Your maximum joist span

How To Make Sure You Have The Right Joist Spacing

To make sure you’re planning your deck frame with the right joist spacing, there are two sets of standards you should check:

  1. Your deck material’s standards
  2. Local building codes

1. Joist Spacing With Composite Decking

Every deck board manufacturer puts its decking material through in-depth independent testing to find the right joist spacing. In almost every case, composite decking manufacturers have found that 16-inches on-center is the maximum joist spacing for their boards. You can find joist spacing requirements in the installation instructions for your deck boards.

One note: that 16-inch spacing is based on a traditional deck board pattern, with boards installed perpendicular to joists. If you’re installing deck boards at a 45-degree angle to your joists, you’ll need to tighten up your joist spacing to 12-inches on center.

2. Local Building Codes

Local building codes can sometimes have different joist spacing requirements. That’s why we always recommend checking in with your city’s building department to make sure your plan meets any local or state requirements.

What's The Maximum Deck Joist Span?

Deck joists have different maximum span lengths depending upon the size, spacing, and framing material that you're creating your deck with. Here's a helpful chart covering the most popular wood framing species and their maximum allowed spans:

This helpful deck joist span chart will help you learn how long your deck joists can be and how far apart to space them based on your deck framing material

The Power of Steel

Steel framing is not only lighter and longer-lasting than wood - it also allows for much longer joist spans.

Below, you can see a comparison between 2x6 joists made of three different wood species and 2x6 steel joists from Fortress Evolution Steel deck framing in two different gauges of steel. The maximum allowable spans are significantly longer with steel joists. In fact, a 2x6 steel joist will provide the strength of roughly a 2x10 wood joist when it comes to allowable joist spans.

Fortress Steel Framing Joists allow for significantly longer spans than traditional wood joists of the same thickness.

To learn more about planning your deck with steel framing, give our team a call at 1-888-824-5316. We've got a team of deck project planners ready to create a plan that helps you create a stronger, safer deck with the best framing materials possible.

A steel deck frame build around a sizable fireplace

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