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How to Build a Shed Base on Uneven Ground

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Anybody who has a house and yard will eventually wish they had a shed. Even if you have a relatively small yard or a zero-lot-line house and don’t need a riding lawn mower, you will have some ground to take care of.

This means some kind of trimming tools and planting tools for any kind of landscaping you want to put in. Then there is sometimes a dead bush or plant that needs to be removed. Maybe you’ll have some leaves to rake.

The longer you live in that place, the more yard tools you’ll find you need. You need someplace to store them, and you already have found out that the garage is not the best place. You need a shed.

The next problem will be your ground. Not everybody lives in a place where all the ground is flat and level. The smaller your lot, the fewer choices you’ll have as to where to place your shed. You may not have any choice but to place a shed on sloping ground. Can it be done?

If so, how? Even if you are buying a prefabricated shed, you’ll need to prepare a foundation and have it ready before your shed is delivered. We’ll give you some tips to consider when choosing how to prepare your slope for a shed.

6 Tips for Building a Shed Base on Uneven Ground

1] How Steep is the Ground? The slope will determine the type of foundation you will need. On slight slopes, you can level the ground by digging it out at the high end and building the low end up with crushed stone on the other. Then you’ll be able to put in a timber skid base or even a concrete slab. If your slope is more than 1 to 20, you’ll probably have to put in another type of base, such as a post and pier foundation to hold up the low side.

The steeper the slope, the more of a drainage problem you’ll have as well. You want to keep any flowing rainwater away from your shed. You may need to put in a drainage system of some type to steer the water flow away from your shed and keep the water flowing around it instead. You may also benefit from installing gutters on your shed.

Not only will water standing or flowing around or under your shed lead to dampness problems inside, but it can wash away some of any gravel you put down under your base. It can also wash soil away from the shed, leaving your base or piers less supported.

In some cases, it can even lead to your shed leaning. For steeper slopes, you may even need some type of retaining wall behind the shed on the high side. For best results, it would need to extend to a greater length than the shed wall it’s protecting to steer the water to the sides.

2] The Shed’s Use. How you plan to use your shed will also figure into this. If you just require a small shed for your long-handled tools with perhaps a few shelves for smaller items, it won’t need the work required to construct or install a shed.

If you need a large shed for a riding mower or other wheeled equipment such as a tiller, you’ll need to plan a little more carefully. The larger the shed, the more the slope will affect it, and the more work you’ll have to put into preparing for a foundation.

3] Where Are You Putting the Door and Windows? You need to plan to have the door on the side that will provide the easiest access. This will usually be on the high side of the slope, but you also need to plan some way to keep rainwater from washing down and right into your shed door. You also don’t want big mud puddles around the doorway.

Another consideration is a window or windows. It’s always a good idea to have a window on a side that doesn’t contain the door. This will allow a cross breeze inside your shed when it’s open. Fresh air circulation helps keep moisture from building up inside your shed and affecting everything inside, including the shed itself.

Damp sheds that are kept closed or that have the window on the same side as the door can easily be affected by mold and mildew, not to mention rust building up on the metal parts of your tools or machines.

4] Where You’re Putting the Shed. You need to really look at the place you plan to put your shed. You may need to plan for the doorway to be on the high side of the slope, but if there’s a tree in the wrong place, you may have a problem getting a wheelbarrow or mower wheeled inside without a lot of maneuvering.

If you have to place your shed on piers, you’ll need to raise your shed somewhat on both the higher and lower sides. On the high side, you’ll at least have skids or floor joists underneath, which will raise your shed above ground level. This means you’ll need a ramp of some type to get them into the shed, and this means you’ll need some distance for the ramp.

5] Access to the Shed. Your shed will have a door, but that’s not all it needs. You need to be able to have good and easy access to the door. You need to have the ground as level as possible in front of the doorway. If you build a retaining wall, your doorway would need to be on the lower side. If you have to put your shed on different length piers to make it level, you’ll need access on the high side.

6] Will You Require a Permit? Most sheds will require some type of building permit unless they are really small. If you live in an area governed by an HOA, you’ll need their approval as well. You’ll also have to find out if there are any zoning restrictions that limit your choices as to shed placement.

If your yard has a really noticeable slope, there may be restrictions on putting in a shed as well. It’s best to go to your local building authority and check everything out before you do anything else. If you need a permit, they’ll tell you what plans and papers you need to submit to obtain one.

They can also advise you about zoning regulations in your area. These cover distance from lot lines and underground or overhead utilities, from other buildings, and possible flooding sites as well. Get more information on Permits in my article Can I Build a Shed Without Getting a Permit?

What Shed Base Options Are There for Uneven Ground?

For a lesser slope, one of the best foundations is a gravel box. This is a box made of pressure-treated timbers around the perimeter. Hold it down by pounding rebar through the lumber down into the ground. Level the soil within the box area, then put down a weed barrier. Put down your gravel and compact it tightly.

A retaining wall made of concrete blocks on the high side is also good. It should be placed far enough from your shed so that you can walk between it and the shed for maintenance. It will also keep rain from splashing off the top of your wall and onto your shed. You’ll need to dig a trench for the wall and put down some perforated pipe at the bottom to steer water out from under the wall. It will help keep your foundation dry. Check out my article What’s The Best Shed Foundation Option For You? for the best options when building on sloped ground.

Is It a Good Idea to Level the Ground Before Building the Shed Base?

If you can level the ground, this is really the best choice. Use strings tied to stakes and evened up with a level as a guide to leveling your ground. Keep checking after you think you have it level to make sure. Leveling just by eyeball is not the greatest idea.

While you can dig out one end and build up the low end, it’s really best to get the ground level to begin with. This will cut down on the possibility of the gravel used to build up the low end getting washed away gradually.

You should also plan to grade a space at least two feet wider and longer than your shed base size. This will be so you can put at least a foot of gravel all around the shed to help facilitate drainage.

Even if you build a retaining wall or put in a french drain to steer water away from the shed, it’s still good to have this extra gravel to help catch the water running off the roof and steer it away. See more options for dealing with water in your shed site in my article What’s The Best Way to Add Drainage Around a Shed?

What Are Some Options for Leveling the Ground for a Shed?

There are basically two options. Either level the ground by digging out the higher parts or use compacted gravel inside a frame to level the ground. Don’t try to cheat by taking the dirt you dug from the high side and using it to fill up the low side. The loose dirt won’t be a solid no matter how you compact it, and the chances of it being washed out eventually will increase.

There are grid stabilizing mats made of polyethylene that will lend a lot of stability to your gravel. They feature a honeycomb grid. You put this down over your level ground, then cover it with gravel. The grid keeps the gravel stable and protects against erosion. It’s a great idea for sloping ground and will provide extra stability if you plan to pour a concrete slab over the gravel.

Best Shed Base Option for Low Sloping Ground

The best option for a low slope is to level the ground first, then put in a compacted gravel base. The aforementioned box will ensure that the gravel stays put. You can then put in a skid or joist foundation or even a concrete pad foundation.

The other option is the retaining wall. This can be used on steeper slopes as well. The soil is dug out into the slope to create a big notch for your shed to fit into with the soil being level on the bottom. The shed rests completely on a foundation that sits on the ground, so no props or piers are needed. A retaining wall is built near the shed on the high side to hold back the slope.

Best Shed Base Option for Steep Sloping Ground

For a steeper slope, the best option is the concrete pier system. This is made by sinking concrete into post holes dug four feet deep. For drainage, pour six inches of gravel into the hole. You can use tube forms made of cardboard for concrete forms, as you’ll need the concrete piers to extend above ground at least six inches.

Once the concrete starts to set, insert anchor ties into them to allow attachment to the wooden posts. The posts should be 6 x 6s if possible. There may be zoning regulations as to how deep your post holes need to be, so be sure to tell the building authority you plan to use them on your visit.

You can put in a joist floor base on top of the wooden posts. Some building codes even require this type of base on steep slopes. You may need some cross bracing, depending on the size of your shed and the height of your posts. It’s a good idea to use it anyway, for peace of mind if nothing else.

Put in some gravel underneath the shed to help steer water away and keep soil from washing out from around the concrete piers. You can use blocks or rocks as a frame to keep the gravel in place.

Another solution is to install treated wooden posts sunk right into the ground, but some local building codes won’t allow this. Soil shifting caused by freezing ground in the winter can move them off-kilter.


Whether you are buying a house or a lot for building one, you can’t think of every possible problem that may come up. Most people, especially first-time homeowners, don’t have a future shed in mind when choosing a house or lot.

You may end up with less-than-perfect possibilities for a shed site, but you can overcome this problem with a little ingenuity. Yes, it will cost more in materials and in sweat equity, but you’ll end up with a stable, useful shed that will withstand all the use you’re going to bring it.



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