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Need help with shed foundation on piers

RitchieRevento | Posted in Construction Techniques on October 1, 2014 09:23am

Hello!

I have a couple of questions about building the foundation for a small shed (8×12). While having some landscaping work done in our backyard, we had them pour four concrete piers for the shed using sonotubes (12′ across, 8′ front to back). The piers are 12″ in dia, and go down about 40″ below grade. The frostline in my area is 36″.

The ground is uneven and slopes from the front of the shed to the back. Because of this, the top of the front two piers is about 11″ above the back two.

My question is what’s the best way to level the foundation? Should I use vertical posts and attach them to the rear piers using a post anchor base, or is it better to use solid/dek concrete blocks? I plan on using 6×6 skids across the front two piers and the rear ones, and then lay a 2×6 frame for the floor on top of the 6x6s.

Thank you for any advice you can provide.

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Replies

  1. gfretwell | Oct 01, 2014 10:18am | #1

    I just did this.

    I am putting in a factory made shed that sets on skids but it is basically the same deal. In your case I would put your 2 beams upright instead of laying flat like I did. I used concrete round block for he form above ground instead of sonotube, just because I had them. Start out by putting up your string line for one wall, establishing one axis. Then use the 3-4-5 trick to put up another string line 90 degrees from that. (9-12-15 in this case) That gets you both axis. Get the strings level and you have all you need to get your post tops level. I started with the one that was out of the ground the fartherest filled that one, theh filled the rest, levelling as I went, tapping the round block down into the concrete until they were level. While everything was still wet I laid in my beams and boards across them to verify everything was still level. I put in HETA20 Simpson anchors for wind tie downs. There are also "J" bolts going up into the beams. I drilled the holes in the beams, set the bolts in the hole and shoved them into the concrete while it was still wet.

    View Image

    1. RitchieRevento | Oct 01, 2014 02:27pm | #2

      Greg,

      Thank you for the reply. I am still a bit confused though and sorry if my questions seem dumb. I want to make sure I understand exactly what you mean.

      When you say "I started with the one that was out of the ground the fartherest filled that one, theh filled the rest," do you mean you poured new concrete on top of existing piers? Or did you add round blocks on top of your piers?

      I have to make up about 11" between my existing front piers and the back ones. Thanks again!

      1. gfretwell | Oct 01, 2014 11:12pm | #5

        I did it all in one shot. I dug the 12" diameter holes and started by filling the first one (the lowest point of the grade) to the top, set a round block on that, filled it and that was the level I built the rest to. Then I started filling the rest, eyeballing the level, set the block and fill it, pushing it down or pulling it up to make it level with the first one.

        I did the 4 corners and then the middle one to match the corners.

        I had my wife mixing the mud in a miixer and I was pouring and levelling so it went fast enough that the concrete did not set up before I was done getting everything right.  If you are using Sonotubes, you can get them level before you start filling them.

        1. User avater
          deadnuts | Oct 02, 2014 12:37pm | #6

          Understood the first time Greg. That's why I say your foundation is not an example of having to re-level a foundation. You got it right the first time. Good job. However, the O.P. didn't.

          Question by him is: what is a good way to re-level it? I believe the best way is to just add to the short piers with concrete. Others have pointed out you can make it up with post(s) in the framing. That's a viable solution as long as you maintain a good moment between floor framing and short post; which is probably why a 2x10 band was suggested with the post. Quite frankly I think that is too much extra material and expense. Seems simpler to drill a few holes and add epoxy and concrete.

        2. RitchieRevento | Oct 02, 2014 12:50pm | #7

          Thanks

          Thank you again, Greg. I now understand what you were trying to say. Also, I appreciate the fact that you took the time to upload a picture.

          --RR

  2. mark122 | Oct 01, 2014 05:47pm | #3

    yes, using vertical post would be fine. you can just build your perimeter box out of 2x8/2x10 (i would opt for 10's) and then just set joist in. use treated lumber.

    1. RitchieRevento | Oct 02, 2014 02:37pm | #8

      Thanks.

      Thank you, mark122, for your response.

      This is the solution I am leaning towards since I am not keen on doing concrete work. If I use a couple of PT 6x6s along the front and back piers, would I still need 2x8/2x10 perimeter box (rather than a 2x6 box)?

      1. mark122 | Oct 02, 2014 06:02pm | #9

        I would not use the 6x6's.

                                                1                               3

                                                2                               4                       

        If the above are your piers, and say 3/4 are your high piers and 1/2 your low ones:

        2x10 from 3-4. (level out), then you can run 2x10's back to  1 & 2, cut your post and complete the box.

        Then space out 2x10 floor joist in the box. If you are going to be loading the shed up with stuff, then you can double up your perimieters if your concerned with the weight on the shed.

      2. gfretwell | Oct 02, 2014 07:40pm | #10

        If the front 2 are level with each other, I am not sure why you wouldn't want to just get more sonotube and pour the back 2 level.

        Use a hammer drill to poke some 1/2" holes in the original piers, drive in some half inch rebar, cut off about 2" below the top of the new sonotube and fill them up. Duct tape the new sonotube to the existing so they don't move on you.

        You are only talking about 3-4 small bags of concrete. I would go ahead and put anchors in the back ones, even if you don't have them in front.

  3. User avater
    deadnuts | Oct 01, 2014 08:05pm | #4

    Do you mean 're-leve'l a foundation?

    Your orignial question, "What's the best way to level a foundation" has a self evident answer: pour it level. Sounds like you already hired a company to put in a level foundation. Unfortunately, you hired the wrong company because a portion of it is 11" out of level.

    I would ask them to fix it...or return the money you paid them to do something that turned out to be faulty. The 11" grade discrepency could have been easily rectified with the inital sona tube pour if somebody was halfway compenent.  However, if you didn't request the oringinal landscaping contractor to pour a level foundation (which you apparently wanted), then it's your fault and you need to fix it. Thus, your question really should be: What's the best way to re-level a particular foundation that was poured out of level?

    Greg's shed foundation is a good example of a foundation that is nice and level---and square. However, it is not an example of fixing an out-of-level foundation.

    My field advice for re-leveling an unlevel foundation: Drill and expoxy 4 pieces of 1/2" rebar into the short foundation piers. Drill them at least 10"-12" into existing piers. Place a section of like size sona tube over these shorter piers to bring them up to the level of the rest and repour this differnece with concrete and metal hold downs cast in place (hold downs similar to Greg's solution will work).

  4. DanH | Oct 02, 2014 07:48pm | #11

    You know, guys, we're talking about a shed here, not the Taj Mahal.  Most sheds this size are just propped up on concrete blocks (if that), so this one's already well ahead in the game.  All the guy really needs is suggestions for the simplest way to achieve a level base.

    1. gfretwell | Oct 02, 2014 10:53pm | #12

      I suppose that depends on where you live. In Florida a shed is built to the same wind code as your house. (150 MPH here)

      I am still not sure what is so hard about putting some rebar in the existing pier taping ~11" of sonotube to it and pouring in a few bags of concrete.

    2. User avater
      deadnuts | Oct 02, 2014 11:18pm | #13

      read the posts

      The O.P's gotten two Dan. And one was repeated.

      BTW, a shed foundation that is almost a foot out of level in 8 or 12 feet is hardly ahead of the game. I'd ask "what's your suggestion?" Dan, but since I know you're 'strucuturally challenged', I don't dare...or care.

  5. DanH | Oct 03, 2014 07:18am | #14

    A lot depends on how high you want the floor of the shed to be, plus where you expect the corners of the shed to be in relation to the footings.  If you want the floor as low as possible there might be a way to effectively suspend the joists below the front footings, or at least run a rim joist between the footings, vs a beam that the joists would sit on top of.  But this gets more difficult if you want the footings concealed below the shed.

  6. renosteinke | Oct 03, 2014 09:35am | #15

    Copy What Works

    8x12 is just large enough that you need a 'real' floor. You will never regret having a firm, solid floor. The bad news is that you might end up having to start over. 

    Does your house have a crawl space? If so, copy what you see, Just, maybe, scale it down a bit for the shorter span. 

    First off, the pilings need toclose to level with each other; your connectors will give youonly a few inches of adjustment.

    That is .... use a metal connector to separate the (treated) lumber from the concrete. Direct contact is a bad thing, even for treated lumber. There will be such a joist along each 12-ft side. I suggest you use 2x10's or 2x12's for these joists.

    Using joist hangers, hang joists no more than 24" on center between the 12-ft. joists. These can be 2x6's or 2x8's.

    Cover the floor framing with 1-1/8 tongue & groove subfloor material, and cover that with a sheet of vinyl flooring.

    Since I'm pretty sure that you don't want the floor of your shed a foot (or more) above the ground, you will have to dig out ground to recess the frame below grade. I suggest you place foamboard - 1/2" thick ought to be enough - on the outside of the framing lumber, then fill in around the high end and sides of the shed. Leave the back open, for air circulation and drainage. You might screen it with hardware cloth to keep the critters out, and lay plastic sheeting under the shed to keep weeds to a minimum.

    Or, of course, you could try various clever 'short-cuts.' My neighbor did that, with a shed of similar size. He's only had the floor collapse three times.

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