Deck Joist Spacing

How far apart should deck joists be?

The deck is one of the most important spaces in your home. It’s an area for outdoor entertainment, relaxation and play and that means it needs to be built correctly. Building a deck requires careful planning and preparation. One component of building a deck is spacing the joists correctly but how far apart should they be?

In this blog post, we will offer advice from experienced professionals about how far apart should deck joists be spaced and why correctly calculating the joist span for an outdoor deck is so important. 

We’ll also provide some tips for ensuring the correct spacing and what factors you should consider when it comes to the spacing of deck joists. So, let’s get started!

Deck Joist Spacing

Common joist spacing for residential decks is 16 inches in the center, meaning the space between each joist is 16 inches. For commercial or public decks, the spacing should be 12 inches in the center or less. Depending on the weight load and span, deck joists may need to be spaced 12 or even 8 inches apart.

Also, when installing decking boards over joists that are greater than 24”, it is best practice to use two pieces of decking on each joist. It is also important to note that when using two pieces of lumber per joist, the joist spacing should be reduced by one inch.

For example, if you are installing 2×6 decking boards over joists that are 24” apart, the deck joist spacing should be reduced to 23 inches. This will help to reduce movement and ensure a more stable deck surface. It’s important to read and understand your local deck codes before construction begins so that you can ensure proper spacing requirements are met.

What are deck joists and what do they do?

Deck joists are the structural components of a decking frame that provide support for the deck boards. They run in parallel along the length and breadth of the deck, with each joist running perpendicular to the ledger board or band board and connecting it to other joists.

Deck joists are typically made from pressure-treated lumber, which adds long-term durability and resistance to rot, fungal decay and warping. Deck joists are essential for creating a sturdy framework and providing support for any load-bearing elements such as hot tubs or roofs that may be added onto the deck’s surface.

Why is the spacing between deck joists important?

  1. Spacing between deck joists ensures that the total load of the deck is evenly distributed among all of the joists, reducing the risk of strain on a single joist and making the structure more stable.
  2. It also allows proper ventilation and drainage. If the joist spacing is too narrow, then it will create weak spots in the deck which can lead to structural issues.
  3. Joists that are too close together may be prone to warping and twisting, resulting in an uneven deck surface.
  4. Proper spacing between joists also allows for the use of more substantial fasteners and provides greater strength against lateral movement, which can occur during periods of high wind or vibration due to nearby traffic.
  5. Finally, it allows for the safe installation of any necessary flashing or other protective material that may be required to keep the deck dry and in good condition over time.
  6. Overall, proper spacing between joists is essential for a safe and durable deck structure.

What are some tips for ensuring the correct spacing between deck joists?

  • Use a framing square or measuring tape to measure and mark the correct distance between joists.
  • Make sure that each joist is level before installing it.
  • Use joist hangers to provide additional support and stability for the deck joists.
  • When using lumber, always use pressure-treated lumber so that your deck will last longer in different weather conditions.
  • Always leave a gap of at least 1/8 inch between the edge of the joist and the wall of the house.
  • Securely fasten all joists to the ledger board with lag screws or other appropriate hardware.
  • Use galvanized nails, stainless steel screws and other corrosion-resistant fasteners when attaching deck boards to the joists.
  • Make sure that each post is securely anchored to the footing.
  • Use a level to ensure that all joists are correctly aligned and spaced.

By following these tips, you can ensure that your deck joists are properly spaced and secured for a safe and durable structure.

Can you have too much space or not enough space between deck joists?

Yes, it is possible to have too much or not enough space between deck joists. If the spacing between joists is too wide, the deck may become unstable and unsafe. On the other hand, if the joists are spaced too close together, there won’t be adequate support for properly installing materials like decking boards and railings.

The ideal spacing for most decks is between 12 and 16 inches apart, though this can vary depending on the size of the decking boards being used.

Additionally, it’s important to check local building codes and regulations to ensure joists are spaced correctly according to safety standards. When in doubt, consult a qualified professional contractor for assistance.

Other factors to consider when it comes to the spacing of deck joists?

  1. Correct deck fasteners: Ensuring that you use the correct type of deck fasteners for your joist spacing is essential for a sturdy and durable result.
  2. Types of lumber used: Different types of lumber can affect the proper joist spacing, as some materials may require less space than others. Be sure to check the manufacturer’s instructions for recommended joist spacing.
  3. Load-bearing capacity: The weight of the deck materials and any other items placed on it should be taken into consideration when determining the proper joist spacing.
  4. Allowance for thermal expansion: If temperatures in your area fluctuate significantly, you may need to leave some extra space between the joists to allow for thermal expansion.
  5. Local building codes: Finally, it’s important to check your local building codes to ensure that your deck meets all of the requirements in terms of joist spacing.

Bottom Line

When building a deck, the most important factor to consider is the spacing of your joists. Joist spacing should depend on the type of decking material you are using, as well as the size and species of the lumber. Deck joists should be spaced no more than 24 inches apart. Setting the joist system properly is essential to having a strong and long-lasting deck.

Ultimately, the best way to determine the spacing of your deck joists is to consult a local deck builder who can provide you with an accurate measurement. We hope this guide helps you in determining the proper spacing of your deck joists. 

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