Most sheds, including my own, don’t really have a shed foundation. Most sheds are placed on concrete blocks. I built my 16×16 shed about eight years ago. When building it, I did what most homeowners do. I built pillars using concrete blocks. Carefully leveling the blocks by either digging and adding a gravel base or using different size blocks. The only point on my shed that did not have a pillar was the right rear corner.
My property is all sloped. The right rear corner was very close to the ground. Consequently, I only placed one block on a bed of gravel there. In retrospect, I should have placed one more block on each of the pillars. This would have raised the shed about four inches and may prevented the problem I encountered over the years.
Why Did the Corner of the Shed Sink
What I didn’t know at the time, was that water tended to accumulate in that particular corner. It wasn’t enough to undermine the shed foundation. However, it was enough to soften the ground there. The water softened the ground enough that the block holding the corner up sunk. It sunk enough to cause that side of the shed to lean. The shed leaned enough that it caused the doors on the side wall to get stuck. I checked this with a level by the door and could see that the floor was out of plumb.
I gave this a lot of thought. The only idea I could come up with was to dig out a portion of that corner and jack up the shed. Tha way I could pour a concrete footer there. I procrastinated a bit before taking this on. Playing out the best case and worse case scenarios in my head (The shed falling on me being the worse one). I finally decided to tackle this and get it out of the way.
Fixing the Sunken Shed Corner with a New Shed Foundation
Digging out the Corner of the Shed
I started by digging out a section next to the corner in question along the back wall. I ended up digging out a section about two feet long and 14 inches deep. Next, I placed a four-inch thick paver in the hole. I put a twelve-ton jack on top of that and a piece of two by eight on top of the jack. What happened next was pretty interesting.
As I tried to jack the shed up, I noticed that the paver was slowly sinking into the soil and clay below it. The more I raised the jack, the more the paver sunk in. I ended up releasing the jack, and placing another, slightly larger, paver on top of the old one and repeated this. Eventually, the pavers stabilized and started lifting the shed.
Temporarily Supporting the Shed
I was able to raise that corner of the shed about an inch and a half Placing two long sections of 2×6 lumber on either side of that corner temproarily supported the shed. These were long enough to straddle both sides of the hole and temporarily support the shed while I feverishly brainstormed on how to put a new shed foundation in.
Setting a base for the New Footer
At that point, I thought the best thing to do is to set some pavers underneath the corner of the shed and sink them in as far as they would go. Sinking a few pavers would provide a solid base for a concrete footer. A concrete footer should be more than enough to provide a stable shed foundation. So I sank a few more of the four-inch pavers into that corner. I used the jack to do this. The original concrete block was still on the bottom corner of the shed, so I placed the top of the jack against it.
After sinking the pavers, I needed to find a way to simultaneously support the shed and seal off a section to pour the footer. At that point, I was left with a jack very close to the corner. This was right where I wanted to pour a concrete footer. I ended up standing a paver sideways, on top of one of the sunk pavers, and lowering the shed on top of it. I checked the level of the floor at that point and found that I was lucky enough to have an almost level floor.
Blocking up the Shed Corner
While the shed was resting on that one paver, I measured the distance from the base of the block underneath the shed to the sunk paver directly underneath it. I cut a piece of 2×6″ treated lumber to that exact length. Once again, I used the jack to lift the shed and placed the 2×6 on the other side of the jack. I now had a piece of 2×4 and a paver on either side of the jack holding up the corner of the shed, and it was almost (slightly off) perfectly level.
Pouring a Concrete Footer for a New Shed Foundation
It was almost ready to pour a footer in that section with one exception. There were were gaps between the 2×6, the paver and the surrounding hole. These gaps would have caused the concrete to spill into the adjacent areas. To fix that, I cut four strips of sheet metal that I had laying around. I used these as dams (see picture below). Next, I backfilled the outside areas with some of the dirt I had removed to add a backing to the sheet metal strips..
After that, it was a simple task of removing the jack and filling in the corner with concrete. I was careful to make sure that the concrete slightly exceeded in height the lower edge of the concrete block that was holding up the corner. I also used a shovel to work the concrete well underneath and past that block. I’m pretty sure that this new shed foundation will hold up well to anything nature has to throw at it!.