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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.

 Beam Sizes (Based on No. 2 or better Ponderosa Pine and Southern Pine Treated for weather and/or ground exposure)

X = Joist Length

X Species         Post Spacing            
  4' 5' 6' 7' 8' 9' 10' 11' 12' 13' 14'
6' SYP 1-2x6 1-2x6 1-2x6 2-2x6 2-2x6 2-2x6 2-2x8 2-2x8 2-2x10 2-2x10 2-2x10
  P P 1-2x6 1-2x6 2-2x8 2-2x8 2-2x8 2-2x8 2-2x10 2-2x10 2-2x12 2-2x12 3-2x10
7' SYP 1-2x6 1-2x6 1-2x6 2-2x6 2-2x6 2-2x8 2-2x8 2-2x10 2-2x10 2-2x10 2-2x12
  P P 1-2x6 1-2x6 1-2x8 2-2x8 2-2x8 2-2x10 2-2x10 2-2x10 2-2x12 3-2x10 3-2x10
8' SYP 1-2x6 1-2x6 2-2x6 2-2x6 2-2x8 2-2x8 2-2x8 2-2x10 2-2x10 2-2x12 2-2x12
  P P 1-2x6 2-2x6 2-2x8 2-2x8 2-2x8 2-2x10 2-2x10 2-2x10 3-2x10 3-2x10 3-2x12
9' SYP 1-2x6 1-2x6 2-2x6 2-2x6 2-2x8 2-2x8 2-2x10 2-2x10 2-2x12 2-2x12 3-2x10
  P P 1-2x6 2-2x6 2-2x8 2-2x8 2-2x10 2-2x10 2-2x10 3-2x10 3-2x10 3-2x12 3-2x12
10' SYP 1-2x6 1-2x6 2-2x6 2-2x6 2-2x8 2-2x8 2-2x10 2-2x12 2-2x12 3-2x10 3-2x10
  P P 1-2x6 1-2x6 2-2x8 2-2x8 2-2x10 2-2x10 2-2x12 3-2x10 3-2x12 3-2x12 Eng Bm
11' SYP 1-2x6 2-2x6 2-2x6 2-2x8 2-2x8 2-2x10 2-2x10 2-2x12 2-2x12 3-2x10 3-2x12
  P P 2-2x6 2-2x6 2-2x8 2-2x8 2-2x10 2-2x12 2-2x12 3-2x10 3-2x12 3-2x12 Eng Bm
12' SYP 1-2x6 2-2x6 2-2x6 2-2x8 2-2x8 2-2x10 2-2x10 2-2x12 3-2x10 3-2x10 3-2x12
  P P 2-2x6 2-2x6 2-2x8 2-2x10 2-2x10 2-2x12 2-2x12 3-2x12 3-2x12 Eng Bm Eng Bm
13' SYP 1-2x6 2-2x6 2-2x6 2-2x8 2-2x8 2-2x10 2-2x10 2-2x12 3-2x10 3-2x12 3-2x12
  P P 2-2x6 2-2x6 2-2x8 2-2x10 2-2x12 2-2x12 2-2x12 3-2x12 3-2x12 Eng Bm Eng Bm
14' SYP 1-2x6 2-2x6 2-2x6 2-2x8 2-2x10 2-2x10 2-2x12 3-2x10 3-2x12 3-2x12 3-2x12
  P P 2-2x6 2-2x8 2-2x8 2-2x10 2-2x12 3-2x10 3-2x12 3-2x12 Eng Bm Eng Bm Eng Bm
15' SYP 2-2x6 2-2x6 2-2x8 2-2x8 2-2x10 2-2x12 2-2x12 3-2x10 3-2x12 3-2x12 Eng Bm
  P P 2-2x6 2-2x8 2-2x8 2-2x10 3-2x10 3-2x10 3-2x12 3-2x12 Eng Bm Eng Bm Eng Bm
16' SYP 2-2x6 2-2x6 2-2x8 2-2x8 2-2x10 2-2x12 2-2x12 3-2x10 3-2x12 3-2x12 Eng Bm
  P P 2-2x6 2-2x8 2-2x10 2-2x10 3-2x10 3-2x10 3-2x12 3-2x12 Eng Bm Eng Bm Eng Bm

Joist sections cantilevered over beams must be calculated as (2x length) for beam sizing.

SYP= Southern Yellow Pine

P P= Ponderosa Pine
 

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Comments, Questions and Reviews

POST A NEW COMMENT

I would like to build a room over my garage. The span down the center will be 34ft 7 inches. Can I span this with 2 2x12 southern pine? Do I need a column in the center?

posted by James hairless at 3/27/2014 3:59:00 PM


This is outside our scope of work. I would consult a local contractor or your building department.

posted by mike at 3/28/2014 11:49:55 AM


on concret footings @ 12 foot spaceings-4x6 treated beams-Joice 16" ctrs.-will they support deck?

posted by sqtdm at 3/27/2014 7:13:20 AM


You should install another footing and post at the center of the 12'' span. A 4x6 beam can only span about 6''.

posted by mike at 3/27/2014 8:40:50 AM


How far can 4-2x12x18'' (pressure treated) bolted together span? I have two 8x8 posts 14 feet apart. What size beam would I have to have to span 14 feet with a 2 foot overhang on each side to equal 18''? Thanks

posted by demeo at 3/25/2014 4:25:16 PM


I have 2 6x6 posts 14'' apart (on center). they are 8'' away from my ledger. My joists are 10'' and will overhang from the beam 2'' on all 3 sides making a 10x18'' deck. Will a 3-2x12x18'' beam be ok? It will sit on top of the two 6x6 posts at a 14'' span. All wood is pressure treated for ground contact. Thank you

posted by DeMeo at 3/21/2014 6:10:27 PM


You will need to add another post and footing in the center of the 14'' beam span.

posted by mike at 3/24/2014 8:57:48 AM


Can I use (3) 2x12''s on top of a 6x6 post with no notch to span 18'' due to not wanting to obstruct windows and will be a free standing deck?

posted by Joe H - All Decked Out at 1/31/2014 9:00:19 PM


I would recommend consulting an engineer. An 18'' beam span is a very large span.

posted by mike at 2/3/2014 9:12:49 AM


ok, so if you recommend a beam of 2, 2x12, would a beam of 2x10, 2x12, 2x10 work? (asthetic reason)

posted by backsight at 7/31/2013 4:18:44 PM


Yes, that would work.

posted by mike at 8/1/2013 8:38:36 AM