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Beam Span Chart Table

The span of a beam is dependent on a few variables. The species of lumber, size of lumber and the load it carries.  Fewer posts on upper level decks are typically more desirable to the occupants and this drives the use of larger framing materials for longer spans.   Beam span maximums are based on a maximum anticipated live load. Building codes for residential decks only require 40 psf.

The longer the joist, the more area of deck the joist supports, and thus the beam supports. For pressure-preservative-treated southern pine no. 2 grade, there is a method that can be used for estimating beam spans for a preliminary design. 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 2x12 beam can span 12 feet; a (2) 2x10 can span 10 feet and so on.

Dimensional Lumber Deck Beam Span Chart

 

The numbers in gray indicate the distance between the support posts. Numbers in blue are joist spans ( beam to beam or house to beam)

  Joist Spans
 Species  Size Beam  6'  8'  10'  12'  14'  16'  18'
Southern Pine   2-2x6  6'-8" 5'-8" 5'-1" 4'-7" 4'-3" 4'-0" 3'-9"
 2-2x8  8'-6" 7'-4" 6'-6" 5'-11" 5'-6" 5'-1" 4'-9"
 2-2x10 10'-1" 8'-9" 7'-9" 7'-1" 6'-6" 6'-1" 5'-9"
 2-2x12 11'-11" 10'-4"  9'-2" 8'-4" 7'-9" 7'-3" 6'-9"
 3-2x6  7'-11" 7'-2" 6'-5" 5'-10" 5'-5" 5'-0" 4'-9"
 3-2X8 10'-7" 9'-3" 8'-3" 7'-6" 6'-11" 6'-5" 6'-1"
 3-2X10 12'-9" 11'-0" 9'-9" 8'-9" 8'-3" 7'-8" 7'-3"
 3-2X12  15'-0" 13'-0" 11'-7" 10'-6"  9'-9" 9'-1" 8'-7"

Douglas Fir-Larch,

Hem-Fir,

Spruce-Pine-Fir,

Redwood,

Cedars,

Ponderosa Pine,

Red Pine 

 3X6 OR 2-2X6  5'-2" 4'-5" 3'-11" 3'-7" 3'-3" 2'-10" 2'-6"
 3X8 OR 2-2X8  6'-7" 5'-8" 5'-1" 4'-7" 4'-3" 3'-10" 3'-5"
 3X10 OR 2-2X10  8'-1" 7'-0" 6'-3" 5'-8" 5'-3" 4'-10" 4'-5"
 3X12 OR 2-2X12  9'-5" 8'-2" 7'-3" 6'-7" 6'-1" 5'-8"  5'-4"
 4X6  6'-2" 5'-3" 4'-8" 4-3" 3'-11" 3'-8" 3'-5"
 4X8  8'-2" 7'-0" 6'-3" 5'-8" 5'-3" 4'-11" 4'-7"
 4X10 9'-8"  8'-4" 7'-5" 6'-9" 6'-3" 5'-10"  5'-5"
 4X12  11'-2" 9'-8" 8'-7" 7'-10" 7'-3" 6'-9" 6'-4"
 3-2X6  7'-1" 6'-5" 5'-9" 5'-3" 4'-10" 4'-6" 4'-3"
 3-2X8  9'-5" 8'-3" 7'-4" 6'-8" 6'-2" 5'-9" 5'-5"
 3-2X10  11'-9" 10'-2" 9'-1" 8'-3" 7'-7" 7'-1" 6'-8"
 3-2X12  13'-8" 11'-10" 10'-6" 9'-7" 8'-10" 8'-3" 7'-10"

  Assumes 40 psf live load, 10 psf dead load, L/360 simple span beam deflection limit, cantilever length L/180 deflection limit, No. 2 Stress grade, and wet service conditions.

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