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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 deck 40 feet long and 8 feet wide. At the lowest point it will be 2 feet off the ground. At the highest point it will be 5 feet off the ground. I would like to use 4x4 posts six feet apart on concrete piers. The ground is cherty and firm.

posted by John Boyle at 8/26/2014 1:53:00 PM


I would recommend using 6x6 posts and a 2-2x10 beam.

posted by mike at 8/27/2014 9:07:31 AM


I am planning to build a pergola over a 16''x16'' patio. 8" concrete footings 42" deep (Minnesota) in each corner, just outside of the patio. 6 x 6 posts 2x12 beams sandwiching the posts 2x6 cross sections laid into 5 1/2" notches in the 2x12s Will that support itself without sagging? Do I need to have more supporting footings and posts? I appreciate the advice.

posted by doughill at 8/20/2014 11:43:37 PM


I would recommend installing center footings and posts in the center of the 16'' spans.

posted by mike at 8/21/2014 9:00:51 AM


hello, i want to build a patio cover. it will come off the house from a 2x8 ledger , using 2x6 for a 11'' run, and using 3 6x6 posts centered 14'' apart for a 30''span aprox. what can i use as a beam to support that span, 3 2x8 nailed together should do it?

posted by marco at 8/20/2014 12:27:44 PM


I would recommend adding one additional post. Otherwise you should use a minimum of 2-2x10 beam.

posted by mike at 8/21/2014 9:02:17 AM


hi mike, i got the footings done for 3 6x6 posts spaced 14''3" on center, for safe side what do you think of using 2 2x12 for beams? from the house wall to the beam is 11'', and the slope is 3/12. what do you think? should i still add more posts? or i should be good with the 2x12''s? let me know please, ty

posted by marco at 8/23/2014 3:07:10 PM


That should work.

posted by mike at 8/25/2014 8:58:47 AM


thank you

posted by marco at 8/26/2014 1:22:21 AM


Hello Mike, I am looking to roof my patio-15''Wx10''L concrete pad. The shingled roof will need to be free-standing. I was wanting to use 4-6x6 posts at the corners, w/ a 1.5ft overhang on the 15'' dim (18'' ledger), and a 2'' overhang on the 10'' dim w/ 2/12 pitch (12'' 2x6 S. pine 16"OC). Is 18'' lumber available, or am I better off adding two more posts to the ledger side? Thanks!

posted by Roofit at 8/19/2014 12:01:09 PM


You should add 2 more posts in the center of the 15 foot side.

posted by mike at 8/20/2014 8:53:49 AM


I am building a 12x12gazebo on an existing deck that was sized for a hot tub. I want to use 6x6 corner posts. Can I get away with double 2x8''s around the top to support the 22 Deg pitched asphalt shingle roof with a 1 foot overhang on all sides?

posted by Raddadd at 8/14/2014 5:52:02 PM


You should be able to use a 2-2x8 header to support the roof.

posted by mike at 8/15/2014 9:05:09 AM


I am building a 23'' wide by 18'' long freestanding deck that will have a 2'' cantilever. I will have 4 posts and three beams. Can I use 4x4 for the posts and 2x8 for the joists which will be 16?

posted by John c at 8/14/2014 11:03:48 AM


I would recommend using 6x6 posts and 2x10 joists.

posted by mike at 8/15/2014 9:08:04 AM


I''ve calculated that I need to install a 4x12 beam. Can I use 2 4x6 beams glues and screwed together or is it better to build a beam with 2 2x12s? Thanks!

posted by Spruceforest at 8/9/2014 7:48:39 AM


It is better to use 2x12''s.

posted by mike at 8/11/2014 9:15:21 AM


I am looking at building a deck 30'' wide by 24'' (from house out). I am going to be using treated lumber for the framing. 2x10''s for the joists (16" centers) and beams. I will have 3 rows of beams, every 8''. Joist hangers at the header and face. At 30'' wide, using 6x6 posts and 2x10''s for my beams, are 4 posts going to be enough for each beam set?

posted by AdamB at 8/8/2014 12:22:17 PM


That should work. Make sure your footings are properly sized. I would recommend 22" diameter footings.

posted by mike at 8/11/2014 9:17:59 AM


Hi, I''m building a rather large freestanding deck. It is essentially three 12''x14'' sections put together to form one 36''x14'' deck. Focusing on just one 12''x14'' section would 6 4x4 posts arranged so that each beam spans 7'' and the joists are 12'' work with 4x6 beams and 2x12 joists 16 OC?

posted by George McLaughlin at 8/7/2014 5:57:41 AM


You should use a 2-2x10 beam an 6x6 posts.

posted by mike at 8/7/2014 9:11:02 AM


Can I use 4x6''s for the posts as long as the long side is parallel to the beams? There are some space issues and cutting down the posts to 3.5" "wide" from 5.5" "wide" holds major appeal.

posted by George McLaughlin at 8/9/2014 4:46:36 AM


Hi, I am building a tree house for my daughter on stilts and have set (4) 10"x4'' footings. The platform is going to be 10''x10'' with an 8''x8'' tree house. I was going to use (4) 6" x 6'' PT posts and 2" x 10" PT joists 16" on center box framing. Do you think this will be sturdy enough? should I go with larger platform material? Thank you, Anthony

posted by adelisle at 8/6/2014 10:00:16 AM


This should work. You will need to use a 2-2x10 southern pine beam if you plan on using footings on the corners. You will want to add some bracing if the platform is above 6'' high.

posted by mike at 8/6/2014 11:46:17 AM


I am building a 16 x 12 deck. I would like to use 2x8 joists, 16" centers. Is it okay to use 2 beams (one on each end) using 3 posts on each beam. Or, should I add a beam that runs in the middle of the 12'' length.

posted by jdavison at 8/5/2014 11:52:14 AM


Do the joists run the 12'' direction? Are the beams cantilevered?

posted by mike at 8/6/2014 8:56:36 AM


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