Ground Pad for Storage Shed

I'm sharing this project with you as an instructable because it turned out very well. The situation was putting a kit storage shed in the back where I have sloping ground. There are also gophers or moles here (underground), which makes the dirt unpredictable.

The shed itself is a Keter Apex 8x6 (8 feet wide, 6 feet deep). It's a walk-in with floor structure included. Their set up instructions only called for "leveling the dirt" before assembling in place.

So this is about a BETTER ground pad. It's quite standard in construction but often misunderstood or made over-complex. The sloping ground only means that a retaining wall (RW for short) is needed. And if the RW is less than three feet tall, it's considered non-structural as a "garden wall" in most building codes that you can build any way you want. On the other hand, if your RW is three feet or taller, better call an engineer because special reinforcements may be necessary.

Relative Cost (remember this is only about the ground pad, not the shed):
Low to Average

DIY Manpower Needed:
Two strong men (or women! — but just to lift the heavy plate vibrator onto and off of transport)

Skill Level:
Intermediate

Special Tools Needed:
Zip Level or water level
Plate Vibrator

Here in my backyard, the slope is gradual but definitely something to consider. There's a long paved walk that comes down the side. I've planted some trees and shrubs there (beyond photo to the left), which helps take up groundwater. But along with clayey-rocky soil, drainage and erosion are always haunting issues. It's good to know where and how rainwater ultimately drains off your site. And have a comprehensive plan. This spot turns out to be an intermediary passage because there's further downslope (even more gradual) across the back.

First thing was calculating the height of the retaining wall. I located the corners of the future shed for a rough visual (in my head, of how it fits). Measure the lowest point with the ZipLevel. Then subtract the highest finish (future) grade at the upslope side. It helps to know (or plan for) the upslope side, too. I'm planning a low-walled raised planter there. So my tiny RW is primarily to protect the side of the shed rather than hold any surcharge of wet dirt.

Although this is not about the shed kit, I want to show the size of the boxes that they come in. My trailer is eight feet long.

After digging for the dirt pad, prepare for the retaining wall. My RW is relatively small but the mortared brick type. This means a concrete footing is needed. Start the base by staking and leveling a 2x4 containment board. Fill with drain rock. Screed and compact the rock by hand.

Pour concrete with a couple of rebars embedded for added strength. The top surface only needs to be level, not trowel smooth. Note that the 2x6 form board was offset from the 2x4 for easy first removal. It's positioned square (90°) with the existing block wall at rear because the RW will follow it, and the RW defines one side of the ground pad. On the other hand, the footprint shape of the drain rock is not important. The 2x4 board will be removed during granite fill to preclude spill out of the drain rock.

A perimeter border is then staked for two inches of fill. It's permanent, so best to use rot resistant material. Pressure treated 2x4 is perfect. Level the top all around and pack the outer soil against it.

Remove form board (off the concrete) after a few days. It doesn't hurt to compact dry the dirt pad first (with the plate vibrator! why not). Crushed granite is then shoveled in, raked leveled and compacted in thin layers with intermittent water spray. The ZipLevel comes in very handy for quick checks.

This is actually easy work for two guys — one operating the heavy plate vibrator, the other shoveling, raking and checking spots.

Once compacted, the pad is ready to support the storage shed. In fact, two inches deep might be oversized here. It's important, however, to use crushed granite — some supply places call it Blue Crushed Granite (or whatever distinction). It's not granite dust. It's not drain rock. It's certainly not pea gravel. It's very hard, heavy, crushed rock of varying-sized, sharply-angled pieces smaller than 1/4" including fines. It compacts well into a very firm ground that remains permeable to water.

I had this many red bricks lying around unused, so it was perfect for the project. Stacking bricks is easy and fun, especially if you have a helper continually mix good mortar to pass to you so you can focus on straightness, level, plumb, pattern, etc. This RW itself also didn't have to look that good for its location. Lucky me.

Soon after tooling the brick RW, the shed can be assembled on the pad, starting with the floor. Masonry sealer will be applied later to the brick, but only on the tops. Next is the instantly rewarding part — assembling the shed (not described here because it's just a kit).

The shed itself was super easy to assemble. It has windows, adjustable shelfs, hooks, even a skylight.

One important next project will be the "landing" area in front because storage stuff needs to roll in and out, and that curb on the left dropping to a sloping ground is still very unresolved — winter rains would cause erosion if unfinished. Gophers or moles also attack the soft soils here.