The formula for the section modulus is beam width times beam depth squared divided by 6. A two 2-by-6 standard beam has actual dimensions of 1.5-by-5.5 inches which would give a section modulus of 1.5 x 5.5 x 5.5 / 6 = 7.6 which is not enough for this example.
Similarly, what size lumber can span 20 feet?
Max. Live Load 60 lbs/ft2 (2873 N/m2)
| Maximum Span (ft – in) | ||
|---|---|---|
| Nominal Size (inches) | Joist Spacing Center to Center (inches) | Lumber Grade |
| 2 x 12 | 24 | 13′ – 2″ |
| 2 x 14 | 12 | 20′ – 10″ |
| 16 | 18′ – 0″ | |
Also Know, how far can you span a 4×6 beam? Obviously, the larger the beam, the greater the distance it can span between posts. A Redwood 4×6 beam should span no more than 6′ between supporting posts.
Likewise, people ask, how far can a beam span without support?
When supporting joists that span 12 feet with no overhang beyond the beam, a double ply beam can span in feet a value equal to its depth in inches. A double 2×12 beam can span 12 feet; a (2) 2×10 can span 10 feet and so on.
How do you size a load bearing beam?
The formula for the section modulus is beam width times beam depth squared divided by 6. A two 2-by-6 standard beam has actual dimensions of 1.5-by-5.5 inches which would give a section modulus of 1.5 x 5.5 x 5.5 / 6 = 7.6 which is not enough for this example. A 2-by-8 beam would be sufficient.