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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 am building a deck 18'' wide X 12'' deep. what would the size of beam needed for the span?

posted by Titanium Joe at 7/14/2014 11:45:13 AM


If you have 3 posts you can use a 2-2x10 beam.

posted by mike at 7/14/2014 12:08:08 PM


Mike I am only using two one on each end. Is this possible?

posted by Titanium Joe at 7/14/2014 1:41:29 PM


You will need to use an engineered beam.

posted by mike at 7/15/2014 8:47:16 AM


I would like to replace a second floor deck that is over another deck. The upper deck is 15 1/2'' ledger and almost 5'' joists. Since its over another deck that is 15 1/2'' x 12'' I don''t want a post in the middle of the lower deck. Would 2 2x12s be enough for a beam with that span?

posted by marsc6 at 6/30/2014 5:27:24 PM


I would check with your local building department. It isn''t covered by our beam span table. You may need to use an engineered beam. Also your existing footings may not be large enough to support the loads.

posted by mike at 7/1/2014 9:06:13 AM


My wife wants to build a deck to put an inflatable pool on. The pool is 12'' round and holds 1700 gallons of water. This will be going up behind our garage. I don''t know if I should attach a ledger or just post it all. I''m thinking 18'' out from the house will give enough space to walk around. I need help with figuring out how to support 14000+ pounds of weight. I know that this is going to be a challenge.

posted by maddeck at 6/25/2014 7:37:18 PM


Placing a pool on top of a deck is not recommended. You should consult an engineer.

posted by mike at 6/26/2014 9:13:33 AM


ok, thanks Mike. I will do that.

posted by maddeck at 6/26/2014 10:21:25 PM


Which is stronger, a 4x6 beam or two 2x6''s as a beam? Or would either work?

posted by Oops at 6/25/2014 2:34:20 PM


Either should work interchangeably if the 2-2x6 is properly nailed together.

posted by mike at 6/26/2014 9:15:27 AM


A 4x6 would be 3 1/2 inches wide, where a doubled 2x would only be 3 inches.

posted by maddeck at 6/26/2014 10:24:14 PM


My son wants to build a 18 '' x 18'' foot deck, due to wanting a open patio underneath he does not want a center support post. Can this be done ?

posted by Kim Wirth at 6/23/2014 8:11:24 PM


He will need to use 2x12 joists installed at 12" on center.

posted by mike at 6/24/2014 9:05:49 AM


I am building a 16''x19'' deck with the 16'' ledgered off the house. I have 6 posts total, 8'' centered coming off the house, and spaced evenly along the length of the deck, making my support beams a 9.5'' length. What size does my support beam need to be? and am I correct using 4"x4" posts?

posted by deperesteve at 6/18/2014 2:15:38 PM


You should use a 2-2x10 beam with 6x6 support posts. Make sure you properly size your footings. The footing in the center should be at least a 22" diameter.

posted by mike at 6/19/2014 9:06:56 AM


Hi All, I would like to build a small deck 8''x10'' legered to my house. The joist span is 8'' and the beam span is 10''. I will have a 6x6 post at each end. What should I do for a beam size (2)2x8 or 2 (2x10). Say for aesthetic reasons, I want a single beam not built up by 2x, would a 4x8 work or would I have to beef it up. Joists 2x8 2x8@16" o.c.? Thank you?

posted by wantadeck at 6/13/2014 5:06:31 PM


A 4x8 beam should work. I would recommend setting the posts in 1'' from the edge of the deck to reduce the span to 8'' from 10''.

posted by mike at 6/16/2014 9:01:59 AM


Mike-thanks for the suggestion about pulling back the posts to reduce the span.

posted by wantadeck at 6/16/2014 1:56:42 PM


I am building a 16'' deck that is attached to a ledger board on the house. It will extend out from the house 14'' How many pilings do I need and how far out from the house should the beam be? Also how many beams do I need. We are using all pressure treated lumber. Thanks

posted by Suzanne-777 at 6/12/2014 2:11:50 PM


You can use 1 beam set back 2'' from the end of the deck with 3 footings and posts. Use a 2-2x10 beam and 2x10 joists.

posted by mike at 6/13/2014 8:46:20 AM


building a 16x16 DECK due to height restrictions I would like to use 2X8 beams and 2X6 joists. How many beams would I need to use with 4X4 posts and joist 16 on center. Would you go 3 or 4 posts wide and how much over hang can you use at the outer edge. Thank you for your help.

posted by Paul Frascht at 6/6/2014 4:06:00 PM


You should be able to build the deck with a beam in the front of the deck and one beam in the center of the deck. You can use 3 posts on each beam.

posted by mike at 6/9/2014 8:59:09 AM


I am building a 16''*16'' deck. One side us going g to be attached to the house with a double 2*10. The other end will be supported with a double 2*10*16 at 14'' from the house, leaving a 2'' canteliever. Is one beam sufficient, or should I be using 2 beams ( one at 7'', one at 15'')?

posted by sdmdecks at 5/28/2014 4:56:34 AM


Oh, and the beam has 3 posts and footings

posted by sdmdecks at 5/28/2014 4:58:06 AM


You only need 1 beam if you use 4 footings and support posts.

posted by mike at 5/28/2014 8:57:42 AM


I am looking to splice 2-2x10x10 with 2-2x10x15 (16s cut down), staggering the splice, to create a 25'' beam span. Do I need extra post support? I have placed a post a foot in on each side and a 9''foot space inwards on each side, in my plans. This leaves a 5'' foot space in the middle. Is that adequate?

posted by Bulatao at 5/7/2014 11:04:15 PM


this would be yellow pine and the deck will be attached. Thanks

posted by Bulatao at 5/7/2014 11:10:24 PM


What is the joist span?

posted by mike at 5/8/2014 9:14:01 AM


I was planning on a 12" joist span. Thanks.

posted by Bulatao at 5/8/2014 6:00:33 PM


You will need another post in the center of the 15'' span or use an engineered beam. You will need to add a post or make the 10'' span a 3-2x10 beam.

posted by mike at 5/9/2014 9:16:25 AM


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