Beam Load Tables
Load-bearing capacity for headers and beams
Beam load tables help determine the appropriate beam size for carrying loads over openings or supporting floors and roofs. Beam capacity depends on size, species, grade, and span.
Douglas Fir-Larch, No. 2 Grade
| Opening Width | One Story | Two Story | Building Width Supported |
|---|---|---|---|
| 3' | 2x6 | 2x8 | Up to 28' |
| 4' | 2x8 | 2x10 | Up to 28' |
| 5' | 2x10 | 2x12 | Up to 28' |
| 6' | 2x12 | (2) 2x10 | Up to 28' |
| 8' | (2) 2x10 | (2) 2x12 | Up to 28' |
| 10' | (2) 2x12 | 4x12 or LVL | Up to 28' |
Southern Pine, No. 2 Grade, 40 PSF Total Load
| Beam Size | 4' Tributary | 8' Tributary | 12' Tributary |
|---|---|---|---|
| 4x6 | 7' - 6" | 5' - 3" | 4' - 3" |
| 4x8 | 9' - 11" | 7' - 0" | 5' - 8" |
| 4x10 | 12' - 4" | 8' - 9" | 7' - 1" |
| 4x12 | 14' - 9" | 10' - 5" | 8' - 6" |
| 6x8 | 12' - 2" | 8' - 7" | 7' - 0" |
| 6x10 | 15' - 1" | 10' - 8" | 8' - 8" |
| 6x12 | 18' - 1" | 12' - 9" | 10' - 5" |
Understanding Load Types
Tributary Width
The tributary width is the area supported by the beam on each side. For example, a beam supporting joists spanning 16 feet would have an 8-foot tributary width on each side (16' ÷ 2 = 8').
Point Load vs. Distributed Load
- Distributed Load: Load spread evenly along beam (joists, rafters)
- Point Load: Concentrated load at specific locations (posts, other beams)
- Point loads require larger beams than equivalent distributed loads
Built-Up Beams
Built-up beams are made from multiple pieces of dimensional lumber fastened together:
- (2) 2x10: Two 2x10s nailed together
- (3) 2x12: Three 2x12s nailed together
- Must be fully nailed with proper nailing pattern
- More economical than solid timber for many applications
Solid Timber Beams
Advantages of solid beams (4x, 6x, 8x):
- Stronger than built-up beams of same size
- No need to nail multiple pieces
- Better appearance if exposed
- More expensive than built-up alternatives
Engineered Lumber
Modern alternatives offering superior performance:
LVL (Laminated Veneer Lumber)
- Very strong and consistent
- Available in long lengths
- Won't shrink, warp, or split
- Common sizes: 1-3/4", 3-1/2" thick
- Can span further than dimensional lumber
Glulam Beams
- Made from layers of wood glued together
- Available in large sizes
- Beautiful when exposed
- Can be curved or arched
- Excellent for long spans and heavy loads
Steel Beams
- Strongest option per size
- Best for very long spans
- Won't rot or burn
- Requires welding or bolting
- May need fireproofing
Beam Connection Methods
- Joist Hangers: For connecting joists to beams
- Post Caps: Connect posts to beams above
- Post Bases: Connect posts to beams below
- Beam Hangers: Support beams from other beams
- All connections must use proper fasteners and hardware
When to Consult an Engineer
Always consult a structural engineer for:
- Spans over 20 feet
- Removing load-bearing walls
- Heavy loads (hot tubs, slate roofs, etc.)
- Multiple point loads
- Complex load paths
- Any uncertainty about loads or spans
Disclaimer: These tables are for preliminary planning only. All beam sizing must be verified by local building codes and/or a licensed structural engineer. Actual requirements vary based on specific loading conditions, support conditions, and local code requirements.