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Old 12-19-2013, 09:55 PM   #1
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Deck joist sizes


I'm going to be building a small deck/front porch for my house soon, and was trying to figure the joist and beam sizes that would be sufficient but economical. see if this looks sufficient. will be using PT lumber
It is a basic 5x10 rectangle deck:
4-4x4 posts sitting on concrete footers
(not sure on beam size i believe the post spacing would mean only 1 2x6 per 2 posts running the length, but don't know if i should go to a 2x8 or 2-2x6's)
joists 2x6 running width
5/4 x 6 decking running length.

what would ya'll recommend on the beam and joists?

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Old 12-19-2013, 10:11 PM   #2
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Deck joist sizes


You'll want to read through the following "bible" of deck building

http://www.awc.org/publications/dca/dca6/dca6-09.pdf

Do not blindly take my advice: use this only for reference. Design your deck based on the tables in the awc document.

On a simple deck of that size, with no point loads (i.e., no hot tub), using #2 southern pine:
  • posts should be 6x6
  • 2x8 joists 16" OC will more than suffice for a 5' span. AWC does not recommend 2x6. You could go 24" OC, but I don't recommend it, even with 5/4 decking.
  • 2-2x10 beam will slightly exceed minimum code for a 10' span. 2-12 will of course be better.

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Old 12-19-2013, 10:59 PM   #3
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Deck joist sizes


IMO, double the 5' 2x6's for beams at each end on 4x4 posts with 1' cantilever. 10' 2x8 joists, 16"oc.

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Old 12-19-2013, 11:02 PM   #4
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Deck joist sizes


i guess the beam running the 5 foot would be better and cheaper as well. any other opinions?
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Old 12-21-2013, 11:05 AM   #5
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Deck joist sizes


6x6 posts are mandatory in most regions now for supporting the deck. 4x4's are for handrail. id never build the deck with 2x6 joists. locally they dont meet code. and for the beam i always go 3ply 2x10
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Old 12-21-2013, 07:34 PM   #6
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Deck joist sizes


Kirk, if your answer was for me, the 2x6's were for beams, 2x8 for joists..... a doubled 2x6, 5' long with a 1' cant. each end, has a span of 3' between them. A 4' span doubled 2x6 (#2 Doug-Fir) can carry 3151# or 1/2 the 10' span load = 788# or 67# per ft. and all the species meet code from that reference. Lowest rated species on page 3, Table 3 is 4'2".

4x4 posts are acceptable with a double member beam on top and a post cap with height restrictions---- read commentary on page 30- C6. So many times I have had to show that page on forums, 7th time on this forum since I first brought that deck link to this forum years ago. Always consult local AHJ for local amendments to codes.

Gary

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