I've ordered a 10x16 shed and building a shed foundation right now.
Basically I did 8 concrete piers and I'm planning to just run four 4x4 timber posts in parallel.
Will that be enough of a support?

enter image description here

P.S> - shed will have five 4x4 runners along the floor, like shown here: enter image description here

Edit 1:

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


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 2x8 now instead for support. wow.

  • Who is the manufacturer and what are their recommendations/specifications?
    – Mazura
    Oct 19, 2016 at 22:02
  • @Mazura kloter farms. their instructions did show 6x6. but also only 6 post vs 8 posts like i did.
    – Dannyboy
    Oct 19, 2016 at 22:49
  • If you're sandwiching 2x8's to get bending strength, and you want to strengthen it a lot further, put 10 gauge sheet steel in the middle. Oct 21, 2016 at 4:19
  • @Harper I dunno if that's really necessary. Where would u I buy 2x8x10 steel?
    – Dannyboy
    Oct 21, 2016 at 12:28
  • It's not necessary unless you really need the strength. Hit the phone book (or whatever people use these days) and find a steel distributor that does retail sales. You'll want to have him cut it to final dimensions, you don't wanna cut steel. Oct 21, 2016 at 19:25

3 Answers 3


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.

  • You couldn't find span tables for 4x4's because the answer is no ;)
    – Mazura
    Oct 19, 2016 at 21:47
  • I couldn't find span tables for 4x4's because few use them horizontally anymore. I'm sure 4x4's can span a certain distance within modern building codes. Where I live, most (if not all) pre-WWII cabins were built using them. Parts of our house still have them (sistered w/ new 2x8's & 10's). Oct 19, 2016 at 21:55
  • As joists, perhaps (assuming it's dimensional lumber with the pith removed)? As beams I think not. Other than as posts I can think of nowhere you use 4x4s, and even those uses are not structural (railings and fences). That link is a good read: "If you don't know why 4x4's are not included in span tables you need to find a competent designer/contractor to design and build the structure."
    – Mazura
    Oct 19, 2016 at 22:13
  • I'll go with sistered 2x8s. should be fine imho. Could be better of course but whatever - this is a shed.
    – Dannyboy
    Oct 21, 2016 at 12:38

Without knowing exactly what the structure of the shed's floor plate is, it's impossible to know for sure.

If this were a deck, for a 10' span and ~5' spacing you'd want something more like double 2x8s (which are about 10X stronger in bending than your 4x4 suggestion). On the other hand it looks like the shed is built with its own joists already that might do the bulk of the work spanning the 10' dimension.

Does the shed manufacturer provide instructions about what kind of support is required?

EDIT: you've said that your 4 beams are actually 8' spans and are going to be cantilevered out 1' on each side. That dramatically changes the situation (for the worse).

First of all it means the floor joists are going to be unsupported at their ends which is a problem that needs to be resolved. Also it means that your cantilevered beams are also going to be picking up the entire weight of the walls, roof, and snow (if applicable). You should probably get an engineer involved to design these four cantilevered beams for you.

Also 6x6 posts are not really much stronger than 4x4s in bending. To make a strong beam you need it to be deep. I'm guessing you're looking at something like double 2x12s but it depends on many factors that you have not specified.

  • Reverse image search of the diagram yields kloterfarms.com, who, "can not stress enough, the importance of your stone pad being level." and mentions using a 4"x 6" Pressure Treated beam to level it if necessary.
    – Mazura
    Oct 19, 2016 at 21:57
  • 1
    @Henry well it's 8 foot span between concrete piers. and 10 foot total wood span. Manufacturer instuctions call for 6x6 with only 6 piers (I did 8). I think Ill go with 6x6s then just to be on the safe side.
    – Dannyboy
    Oct 19, 2016 at 22:59
  • @Dannyboy: I've updated my answer. I don't see how they possibly would think that three 10-foot 6x6s would hold up that whole building so I am not really sure what we're looking at. The website also seems pretty clear that this whole thing should rest on a crushed stone pad, maybe they intend for the stone to be there as well?
    – Hank
    Oct 19, 2016 at 23:30
  • @Henry yeah. dunno. Kloter farms cites CT code in their pier foundation drawings. Also they warranty their foundation for 30 year - so im pretty sure it worked for them. I've updated my questions with the pdfs of their foundation requirements, They do offer 2 options for foundation -> either 6 6x6 piers (no concrete) or crushed stone pad. I didnt like the idea of just burying wooden posts in the ground and so I've decided on my own to do concrete piers instead.
    – Dannyboy
    Oct 19, 2016 at 23:37
  • @HenryJackson hmm.I've just realized that I've made another mistake: diy.stackexchange.com/questions/101345/…
    – Dannyboy
    Oct 20, 2016 at 15:24

No. 4x4s are literally off the charts. The only place they belong is as posts.

If you're going to build it like a deck, then build it like a deck (Chicago's deck code). Beams are to be at minimum a 2x8 or a 6x6. If I'm deciphering the 9.1 table right, even two Southern Pine 2x12s only gets you a span of 9'11'' when spaced 4' apart (8' apart is also off the chart).

"Beam undersized for span"

Are you within the manufacturer's specifications (if you use 6x6s)? Yes.

Are the manufacturer's specifications sorta wack? Also, yes.

Supporting a 10x16 foot shed on three (or even four) 6x6s doesn't sound right to me at all. It should be more like eight of them; one every two feet.

  • gotcha. I think Ill fix this by raising the level using short 4x4 posts and on top of them will do 6x6 beams using 4 to 6 inch simpson strongtie adapters. Again - that is 8 ft span, not 10 - and this would imho even beat manufacturer required spec as Im doing 8 posts versus required 6 (that they warranty for 30 years).
    – Dannyboy
    Oct 19, 2016 at 23:10
  • According to my crazy deck codes (again, assuming I'm reading them right), you'd need a 6x6 every two feet to get anywhere close to the proper support for a ten foot span. But if you're going to use 6x6s instead of 4x4s, my reaction goes from absolutely not, to meh.
    – Mazura
    Oct 19, 2016 at 23:14
  • I've added manufacturer requirements for the foundation to the original questrion. Hope it makes it clearer. Srry I think I wasn't clear about "joist ?" span -> it's actually only 8 ft span between concrete piers. And 10 ft total span. And with 8 columns Ill be beating required 6 piers. Also manufacturer is calling this CT code requirenments. afaik as along as code s fine with this - I feel meah and or ok as well :).
    – Dannyboy
    Oct 19, 2016 at 23:24

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