Concrete – Is 4 ten-feet 4x4s enough for a shed foundation

concretefoundationshed

I've ordered a 10×16 shed and building a shed foundation right now.
Basically I did 8 concrete piers and I'm planning to just run four 4×4 timber posts in parallel.
Will that be enough of a support?

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P.S> – shed will have five 4×4 runners along the floor, like shown here:
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Edit 1:

Here's the manufacturer spec for the foundation.
According to the manufacturer this is according with CT building code:

http://imgur.com/a/KOQ2M

Edit 2: Well shoot. I've just realized that I've made a terrible mistake.
Manufacturer chart called for 8 ft on center (so 1 ft would be sticking out on each side). I've build it with 2 ft sticking out -> so 6 ft between concrete posts… wow. ho w th hell did that happened. I think Ill be using sistered 2×8 now instead for support. wow.

Best Answer

4x4x10 (spaced 4'0" apart) is rather questionable and I would expect it to sag in the middle where the shed "runners" (labelled #10 in diag.) rest in the middle of the 10'0" span. If the shed floor joists (FJs) (#9 in diag.) are attached to the runners (#10) the sagging could be minor.

4x4's are inferior to sistered 2-2x4's because the grain in 4x4s is directionally uniform, whereas, 2-2x4's will have differentiated grain.

I couldn't find a link to a span table for 4x4's but found this one (which recommends 2-2x10's for a 10'0" span): span table However, this assumes underlayment only and your shed has runners and FJs.

While I think 4x4x10 is "doable", I think (sistered) 2-2x6's should be a minimum. It really depends on what the live weight load will be (ie. what's going to be stored in the shed...especially toward the center). In my 6x10 shed I used 2x10x6'0" (@ 24" center) with a 2x12 rim joist.

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