Wood and Composite Decking Joist Spacing

Building your dream deck should be a positive and fulfilling experience. A backyard deck provides the simplest way of expanding your living space outdoors, and can be attached to the house or freestanding.

The Decking Superstore regularly stocks softwood and exotic hardwood species, and is available in a selection of thicknesses, widths and lengths as shown in the table below. Below are some diagrams, span chart tables and common definitions to help kickstart your decking installation project. Please be sure to check with your local building authority about what span is required in your area.

What are Joists used for?

Joists are like the backbone used to build a deck frame. The minimum size joist to be used in deck construction depends on the number of posts and beams that will be installed.

What are Beams used for?

A beam is the main load-bearing element of a deck, and provides the structural stability of your deck. It supports the weight of the joists.

What spacing should I use for my Deck Joists?

In typical deck construction, with a ledger board on one side of the joist and beam on the other, the size of the joists is driven by the size of the deck and based on the general maximum spans mentioned above. The span chart below offers conventional joist spacing sizes and meant to have nearly zero deflection under standard loads. Please contact your local permit and building code department for proper joist spacing requirements. The joist spacing shown is also valid if the decking is laid in a diagonal pattern to the joist.

Joist Spacing For Softwoods

Joist Spacing For Hardwoods

The layout term for joists is “on-center” which is the center-to-center measurement from one joist to the next. Most decks use 16″ on center spacing for joists. Most softwood decking is not strong enough to support longer spans than 16″, but thicker hardwood can support greater. Some builders reduce joist spacing to 12” on-center to strengthen the deck frame or to increase maximum allowable joist spans.

Joist Spacing for Composite Decking

Most composite decking materials, like Trex, AZEK, TimberTech and Fiberon composite decking, require minimum joist spacing for composite decking at 16″ on-center spacing for straight decking and 12″ on-center joist spacing for 45-degree angle diagonal decking. For the brands listed above, please be sure to consult with the installation specific brand pages.