Should I Use 2×6 Or 2×8 For Deck Joists?

When It Makes Sense

• Good fit: A modest, residential deck with a 6‑foot span between supports and a light load (e.g., occasional foot traffic) where code tables permit 2×6 lumber. The smaller dimension reduces material cost and simplifies handling.
• Good fit: A deck built on a sloping site where the joist depth can be used to achieve a flatter deck surface without adding additional framing. Using 2×8 joists may allow a shallower beam height while still meeting span requirements.

When You Should Avoid It

• Warning sign: When the deck must support a hot tub, large planters, or a high concentration of furniture, a 2×6 joist often lacks the required moment capacity, increasing deflection and risk of failure.
• Warning sign: In jurisdictions where the building code requires a minimum joist depth for a given span, using a 2×6 that falls short of the prescribed table can lead to non‑compliance and future liability.

Pros and Cons

Pros

• 2×6 joists are lighter, cheaper, and easier to cut and install, which can lower labor and material expenses for small projects.
• Using 2×8 joists provides greater stiffness and load‑bearing capacity, allowing longer spans without intermediate support and reducing perceptible bounce.

Cons

• 2×6 joists may require closer spacing (e.g., 12″ on center) or additional supports, potentially increasing overall framing complexity.
• 2×8 joists are heavier and more expensive, and the deeper profile can interfere with ceiling heights or require deeper footings for supporting beams.

Decision Checklist

• What is the maximum unsupported span and anticipated live load for the deck?
• Do local building codes or a structural engineer specify a minimum joist depth for your design?
• Is your budget flexible enough to accommodate the material cost difference, and will the longer span benefits of 2×8 outweigh that cost?

Alternatives to Consider

If neither 2×6 nor 2×8 feels ideal, explore engineered joist products such as I‑joists or laminated veneer lumber (LVL) that combine strength with lighter weight. Alternatively, reducing joist spacing to 12″ or adding intermediate posts can allow the use of 2×6 while still meeting load requirements.

Final Recommendation

For most standard residential decks with typical foot traffic and spans under 8 feet, 2×6 joists are a cost‑effective choice when installed at 12″ on center and approved by local code. For decks that exceed 8‑foot spans, support heavier loads, or where you desire fewer support posts, 2×8 joists provide the necessary strength and stiffness. Always verify your design against the latest International Residential Code (IRC) tables or consult a licensed structural engineer before finalizing the joist size.