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I built a gravel foundation for an 8x14' prebuilt wooden shed. I spent a lot of time addressing drainage and most aspects of the foundation. Now it is finished, I think, but I want more experienced opinions on leveling it.

Here is the shed foundation nearly finished with rough leveling and compacting:

gravel shed foundation

The core of the pad is mostly crusher run which my local quarry had as more sand than stone, meaning it compacted well but may not drain as well. The perimeter has a french drain-style trench filled with #2 stone and much less sand, so drainage should be okay.

The way I leveled it is using a long 1"x8' board and a 2' level. I roughly leveled the subsoil to have a slight grade for drainage, tamped it. Roughly leveled a central 4"-deep pad of crusher run with a slight consistent grade for drainage, tamped it. Then more carefully did iterations of filling edges with #2 stone and topping it all off with another few inches of crusher run. I raked, scraped, tamped, leveled using the board, and repeated, aiming for a completely level surface. Board and level shown below:

board and bubble level on gravel foundation

I am asking about how to check if it is good enough now. I put the board down with the level in the middle of it, and I checked level in 9 location with the board east-west (16+ft length) and another set of spots north-south (8ft length). In each location the bubble is either balanced, or has only a slight dip on either side (I can pick the low side up 1 inch or less and get the bubble balanced).

I figure the bubble does not need to be perfectly balanced everywhere, it is good enough to be mostly balanced or within an inch of balance in all locations. My reasoning is that the shed will sit on long skids thus distributing its weight and 'averaging out' the slight (0-2 inch max) dips or rises that might remain over the whole area. Also, even if I got it perfectly level at this point, settling may not be perfectly even, so level within an inch seems good.

Is this foundation level enough to receive a shed? If not, what steps should be taken to get it even more level, or what measurements should be made to ensure it is good enough?

The shed will be used for garden tools, as a workshop, and as a small weekend cabin. Most buildings I've lived in are not perfectly level, so being slightly off doesn't seem too troubling to me, but I also have never built or worked in such a small building.

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    1 inch over a 2 foot level doesn't strike me as particularly even.
    – FreeMan
    Nov 24 '20 at 19:32
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    @FreeMan ;) If i understand correctly, the level was on an 8' board. A garden shed on skids does not strike me as requiring better than 1" over 8'.
    – Alaska Man
    Nov 24 '20 at 19:42
  • I describe the "string and stake" method here. It works. Just set your strings dead level rather than sloped as in that question. diy.stackexchange.com/a/52671/18078
    – Ecnerwal
    Nov 24 '20 at 19:48
  • What are the specs on the prebuilt shed? I would purchase a laser level or similar type of device and measure both directions. Pre built have to be quite flat but built on site can be a foot off. Check with your manufacturer but a self leveling laser level can be found online for 30$ or less measure both directions to assure accurate measurements.
    – Ed Beal
    Nov 24 '20 at 19:53
  • Thanks for the input folks. @FreeMan, as Alaska Man said, I used the 2' level in the center of an 8' board.
    – cr0
    Nov 24 '20 at 23:53
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I've built and owned several sheds on similar bases. What you'll find is that the weight of the shed and the vibration of use tends to settle the foundation (floor framing) into the soil a bit, eliminating slight wiggles in the surface.

The key is that you have a good average, and that it's level in both directions. Obviously most of the weight rests on the perimeter, so you want to focus on that. Make sure there aren't any areas that seem weak, like they'll slough out when the shed is set.

Once it's set and has a chance to settle a bit, but before you load it up with human junk, check the floor in both directions. If it's out more than say 1/2" total in either direction (my standard; yours may differ), consider levering it up and making adjustments. That's not as difficult as it may sound if you use adequate levers and suitable fulcrums. Either rake a bit of soil out from under the high side, or fling a bit more under the low side.

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  • This makes sense to me. I did try to tamp and level the perimeter especially well, thinking that will be where points of failure (settling different amounts) would be the worst. It is more level on the 14' stretch than on the 8' stretch, but both are 'pretty good'. Checking the shed's floor will help, as the flatness will more accurately highlight off-level in any direction. In case it needs adjustments, I will need to learn more about levering up the shed - if you have tips that would be helpful! Thanks again
    – cr0
    Nov 24 '20 at 23:57

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