FLOOR JOISTS INFORMATION

Most Common & Recommended Choices

• 2×10 Lumber — Best All-Around Choice
  • Why: Excellent strength-to-cost balance
  • Typical span: ~14–16 ft (16” on center, depending on species)
  • Use when: Standard residential floors
  • Species: Southern Yellow Pine (strongest, best span)  Douglas Fir–Larch (very common and reliable)
  • This is the default choice for most houses.
• 2×8 Lumber — Shorter Spans
  • Typical span: ~11–13 ft
  • Use when: Smaller rooms, additions, cabins, decks
  • Pros: Cheaper, lighter
  • Cons: Can feel bouncy if pushed to max span
• 2×12 Lumber — Long Spans / Heavy Loads
  • Typical span: ~17–20+ ft
  • Use when: Large open rooms, fewer support beams
  • Cons: Higher cost, heavier, sometimes overkill

Other Considerations

: The grade of lumber and species are very important factors in joist strength.

Best choices (in order):

1. Southern Yellow Pine #2 or better
2. Douglas Fir–Larch #2
3. Hem-Fir #2 (shorter spans)

Avoid low-grade or unknown species for structural floors.

Spacing Matters

• 16” on center (standard): Best stiffness and feel
• 19.2” on center: Sometimes allowed, less stiff
• 24” on center: Only with engineered design or thick subfloor

Subfloor Pairing (Important)

• 2×8 joists: Minimum 3/4” T&G OSB or plywood
• 2×10 or larger: 3/4” is standard; 7/8” preferred for premium feel

When Engineered Joists Are Better

Engineered Joists (e.g. I-Joists or LVLs) when you want long spans, more flat floors or desire easy hVAC and plumbing runs.

AS ALWAYS, CONFORM TO LOCAL BUILIDING CODES AND CONSULT PROFESSIONAL ENGINERING SPECIFICATIONS FOR ALL CONSTRUCTION AND DO NOT RELY SOLELY ON THESE CALCULATIONS.  CONFIRM THEM WITH AUTHORITATIVE SOURCES!