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We have a roughly 10x30 elevated wood deck off the pack of our house. The joists are all 2x6 16oc. The posts are 4x4 and are holding up a beam that the joists hang off of with joist hangers. I feel this deck is under built, though I will say it feels very solid for what it is.

I plan on doing the following:

  • add a beam under the joists a foot or so in (to lessen the initial span).
  • use 6x6 posts.

The big question: Do I need to replace the 2x6 joists and make them larger?

I'm finding mixed answers out there on the internet. Some span tables include 2x6 and claim about a 9'6" span when 16OC. Others simply say "don't use 2x6 joists.

If I do have to replace the joists, we're probably looking at a full tear down and starting from scratch. I can live with that, but if I can save the time, money, and extra waste going to the dump by keeping the 2x6s, I'd be certainly for it.

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  • If you are going to add a beam, wouldn't it be better to add it at the midspan, 5' in?
    – batsplatsterson
    Nov 16 '15 at 22:16
  • @batsplatsterson not according to any of the span tables...and--I think--mathematically, you'd want it no further than 1/3 the way in anyways.
    – DA01
    Nov 16 '15 at 22:40
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According to the table in the 2012 IRC code a exterior deck needs to handle a 60lb per sq ft (40 lb live + 20lb dead load). Most treated lumber that I am aware of is #2 southern yellow pine, using that criteria on the table in the code book, your joists can carry a 10'-9" span.

The biggest failure in deck construction has not been the posts or the joists, but the connection to the house. I believe code now requires through bolts into the band joist, or the joist of the house, or posts at the house is cool too.

The length of the post will dictate whether they need to be 4X4 or 4X6. Its a deflection (bowing) thing. IMO 4X4 for a 10' span is not overloading the post, a 16' span may...

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  • Sounds like 2x6 might be OK, then. I definitely plan on ensuring the rim joist is a) still solid and b) attached properly with lags and earthquake strapping. As for the 4x4s, I'm in WA state and from what I can tell, they just aren't allowed on elevated decks. Min is 4x6.
    – DA01
    Nov 16 '15 at 18:30
  • I am in WA too I will look at the seismic charts and connections
    – Jack
    Nov 16 '15 at 20:00
  • Could you sister 2x4s on the 4x4s to meet code?
    – batsplatsterson
    Nov 16 '15 at 22:13
  • Technically it might be something that could be done, but I would not go that way.
    – Jack
    Nov 17 '15 at 1:49

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