Floor Joist Spacing for a 20x20 Shed

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  #1  
Old 01-29-16, 05:44 PM
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Floor Joist Spacing for a 20x20 Shed

Hi! I'm going to be building a 20x20 shed, and I plan on using five 4x4 skids to rest the frame on. How much spacing do y'all recommend for the floor joists? Should I use 2x6s or 2x8s?

Thanks!
 
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Old 01-29-16, 05:58 PM
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If you plan to use skids, then the size of the joists make no difference, for the simple reason that the skids are the base of your structure. I would rethink the use of skids.
 
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Old 01-29-16, 06:06 PM
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2x6s on 24" centers, with 3/4" tongue and groove would be fine. I would suggest that you clear your plan with your local building department, as 20x20 is outside the realm of a "shed". Once you reach a certain amount of sq ft, they will require a footing and foundation.
 
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Old 01-29-16, 06:07 PM
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So I should just rest the frame on blocks? How far should I space the blocks?
 
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Old 01-29-16, 06:11 PM
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Or should I stick with the skids and use smaller joists? Like XSleeper says?
 
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Old 01-29-16, 06:20 PM
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As X said, you need to determine what your local code requires before we go through the process of how to build it.

If it needs a rooting and foundation or a slab base, then skids or blocks are out.

Bud
 
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Old 01-29-16, 06:33 PM
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I'm able to build it with blocks and skids; I just have to present them with the plan before I build.
 
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Old 01-29-16, 07:12 PM
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If they aren't requiring you to put it on a footing below frost, I would at a minimum suggest you make a level surface for your skids to sit on. You can certainly dig cement blocks (such as 4x8x16"solids) into the ground (I'd recommend no more than 5' on center...) and level them, then set the skids on that, but keep in mind that your ground will heave each year with frost, causing your cement blocks to move unevenly... causing the shed to move and that means that eventually it will no longer be level, which can cause problems with doors not opening or closing correctly.

Put a lot of effort into getting those cement blocks level. Don't over dig the ground below each block or you will just make them more likely to sink/settle in the freshly disturbed soil.
 
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Old 01-29-16, 07:21 PM
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Can I use blocks instead of sonotubes? I was thinking about using shims to level the surface for the skids.

On the other hand, do I have to use skids? I was planning on using skids every couple feet to prevent bowing, but if I use 2x10s would I still need them?
 
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Old 01-29-16, 07:33 PM
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You caught me... I edited out the sonotubes, after I wrote it and read it, it sounded unecessarily complicated.

You definitely want to build it on skids... 6x6 would be way better than 4x4, and if they are 5' on center that will provide a nice base for the floor joists which would not need to be bigger than 2x6 because they would only be spanning the 4' 4" space between your 6x6s.

Don't use shims at all! Dig the soil so that the block sits level. You can get a variety of thicknesses of solid cmu... so if your grade has some slope, you can stack the solids one on top of the other in what ever combination you need in order to level them up. But move the soil so they sit level.
 
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Old 01-29-16, 08:05 PM
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I was planning on using a plate compactor on the soil before laying the blocks, and then digging the soil like you said for the blocks to sit level. How does that sound? I will look for blocks in different thicknesses and use them to level instead.

And just out of curiosity, how did you get 4 ft 4 in span between the skids? If the skids are 5.5 in wide and 5 ft on center, wouldn't that be 54.5 inch span? Which would be 4 ft 6.5 inches right? Just trying to get everything right.
 
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Old 01-29-16, 08:09 PM
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If a 6x6 is 5' on center, and they are 5 1/2" wide, it would actually be 4' 6 1/2" of unsupported space between each 6x6... you are right. I had a long day. Lol
 
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Old 01-29-16, 08:34 PM
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Haha I hear ya man no problem. I'm not finding 20 ft. 6x6s, so I will be making the base 16x16 with 4ft on center skids and 16 inch on center 2x6s. Does that sound good?
 
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Old 01-29-16, 08:54 PM
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Also, for insulating the floor, do I stuff the bottom with the appropriate insulation and secure with something like the Tyvek homewrap?

Or could I close the bottom with plywood and then lay the insulation from the top?
 
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Old 01-30-16, 07:43 AM
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Critters love to build in insulation, I'd close the bottom with plywood.
 
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Old 01-30-16, 07:59 AM
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If you have a menards in your area, they can order in 6x6x20' but if you are going 4' on center, 4x4x20 would be okay. Right now they are $32 ea. Their Web site can give you an idea of how long the wait would be... my store says 2/5/16.... so about a week.

This is quite the project. To plywood the bottom, you would need to frame your floor joists, sheath the bottom using 1/2" treated plywood, apply tyvek if you like... attach your 4x4 skids perpendicular to the joists with ledger lok lags, then flip the entire thing over to insulate and sheath the floor. To do that you would need a lift / Lull and some eyebolts... maybe through bolted to your skids. Skids are often tapered on the ends like snow skis on the ends I case you need to drag / pull it somewhere.
 
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