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

When It Makes Sense

• Good fit: Use 2×6 when deck joist spans are short (typically 8 ft or less) and the intended load is limited to normal foot traffic, chairs, and lightweight furniture. In many residential backyards this configuration satisfies the minimum requirements of the IRC and keeps material costs and overall deck weight lower.
• Good fit: Use 2×8 when the design calls for longer spans (9‑12 ft), higher live loads (hot tubs, planters, or gatherings), or when you want additional stiffness to reduce bounce. The larger cross‑section also provides greater capacity for attaching ledger boards and supports on uneven footing.

When You Should Avoid It

• Warning sign: Selecting 2×6 for a 12‑ft span or for a deck that will regularly hold more than 40 lb/ft² (the typical residential live load) will likely violate code span tables and could lead to sagging or failure.
• Warning sign: Opting for 2×8 on a very small, low‑load deck where the joist spacing is already narrow (12‑in spacing) may be unnecessary expense and add excessive weight to the supporting structure.

Pros and Cons

Pros

• 2×6 joists are lighter, easier to handle, and usually less expensive, which can reduce labor time and material cost on modest projects.
• 2×8 joists provide higher load capacity and longer allowable spans, offering greater design flexibility and future‑proofing for added amenities.

Cons

• 2×6 joists may require closer spacing or additional support to meet code for longer spans, potentially offsetting the initial cost savings.
• 2×8 joists are heavier and cost more, which can increase transportation, handling difficulty, and overall project budget.

Decision Checklist

• What is the maximum joist span and the intended live load for the deck?
• Does my local building code permit 2×6 joists for the planned span and load, or does it require 2×8?
• Have I accounted for future loads (e.g., hot tub, extra furniture) and the additional dead weight of larger joists?

Alternatives to Consider

If neither size feels comfortable, engineered lumber such as LVL or I‑joist sections can provide superior strength‑to‑weight ratios and span capabilities, though at a higher price point. Alternatively, using 2×6 joists with reduced spacing (e.g., 12‑in on center) or adding blocking can improve stiffness without moving to a larger dimension.

Final Recommendation

For typical residential decks with spans up to 8 ft and normal foot traffic, 2×6 joists at 16‑in spacing are usually sufficient and cost‑effective. When the deck will exceed those spans, support heavier loads, or you prefer added stiffness, upgrading to 2×8 joists is the prudent choice. In all cases, verify the local building code and consider consulting a structural engineer or qualified contractor to confirm that your design meets safety requirements.