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researcher
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# Posted: 19 Aug 2010 13:28 - Edited by: researcher
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What is the appropriate distance between concrete piers for a foundation? I will be using 2 x 6 for the floor joists 16" on center. For a 12' x 12' floor, I planned on 9 piers. One at each corner, one in the center on each outside side, and one dead center, like so:
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Is that overkill? That's 6' gap between piers.
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nathanprincipe
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# Posted: 19 Aug 2010 14:26
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Researcher, are your intentions to put the frame right on the deck blocks w/o using beams? if so, my concerns are that their are still some joist that will have to span 12' w/o any support. I believe minimum code will tell you that acceptable but you will still have a sag in your floor. You can eliminate that concern by starting with your peirs then running 3 seperate beams along the peirs, then comes your floor joists on top of the beams. This may sound like over kill but I believe it neccessary. If you were building a 8'X12' structure there would be no cause for alarm, as a 2"X6" can comfortably span an 8' length
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researcher
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# Posted: 19 Aug 2010 15:03 - Edited by: researcher
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At this point the plan is to put the frame right on the piers, yes. But, the maximum span of any joist will be 6' (see attachment jpeg, the gray circles are the piers). There will be piers at each corner, a pier dead center, and piers at the midpoint of each outside side. The center beam will run 12' total, with support at each end and support in the center. In the pic below, the beams running left to right (top, center, bottom in picture) are solid, 12' beams. The beams running up and down are 6' beams attached to the center beam. (the close up picture shows it more clearly).
Is it a problem placing the frame right on the piers? Should the center support joist (center, horizontal in the picture) perhaps be a double beam for added strength since it is holding the weight of 5 6' beams on either side?
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nathanprincipe
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# Posted: 19 Aug 2010 16:56
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OK, Im on board now, In your first illustration I mistook your center joist for blocking inbetween 12' joists. I believe you are in good shape with your design, and I cant think of a valid reason why putting your floor frame right on piers would not be a good idea, as long as all your spans check out ( and they do). If you are going to double up on any joists tho it should be all of you outer joists ( rim joist) because they will be bearing the entire load of the walls and roof, I see no reason to double up on you center joists. You also may find it helpful to use joist hangers to attach all of your 6' joists to your rim joists and center joist, It will cost a little extra but will increase the strength of the floor
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researcher
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# Posted: 19 Aug 2010 20:44
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Ok, cool. Thanks for the help.
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rob_o
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# Posted: 20 Aug 2010 18:28
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If you choose to use that design, double or triple up the center joist as well. As you mentioned in your earlier post, the load on all your short joists will be passed into the center and over time *could* cause the center to sag
2 rows of piers with the joists cantilevered over beams would be simpler to build. I also believe it would be stronger but I don't have the math to back that opinion up
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Gary O
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# Posted: 21 Aug 2010 08:48
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I've gotta jump in here.
If there is one place to overbuild, it's the foundation.
I too don't have the math to back it up, but that looks like to few of piers for the distance for 2 x 6s, but with your design not many options present themselves.
I've always just layed beams on blocks 2' apart (no joists) tied in with super thick T&G 1 1/8" ply or 2 x 6 planks for sub-flooring.
Built 12 or so cabins/sheds over 40 yrs, no saggers.
I'd go with Rob O's suggestion at the very least
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