A few months ago I decided to purchase and install a vinyl shed. My problem was that the area I was going to put it was on the side of a hill. While I could’ve dug out some of the hills, I didn’t want to break my back! So, how to build a shed foundation on uneven ground? I decided to sink some 6×6’ posts into the ground on top of concrete footings. From there, I just built a deck for the shed to sit on.
When deciding how to build a shed foundation on uneven ground, it’s best to review your local building codes to make sure your posts are deep enough. If so, go ahead and build your platform just as if you were building a deck. Once installed, you can go ahead and assemble your shed on the platform. If you put your posts on sonotubes, install plenty of cross bracing to limit foundation movement.
The great part about building on a slope with post and beam construction is that you can use the space beneath the beams for extra storage. You could enclose the space and add a small door, or make your posts slightly higher to have more space. Just be sure you make your deck box strong, you don’t want any sag when you park your riding mower in there.
Things To Consider When Building A Shed Base On Uneven Ground
Uneven ground is what most of us will encounter when building a shed base. While it may require a little more time and effort, you can make a shed base on the uneven ground pretty easily.
It all depends on the grade of your slope. If it is steep, then you’ll probably use a different type of base than a slight grade. Let’s take a look at some factors to consider when dealing with uneven ground.
How Steep is the Ground?
This is your main issue. First, consider your ground type. Is it exposed rock? Clay? Or can you dig easily? All of these factors are important.
If you are on solid clay, digging might be a pain. On the other hand, a steep slope might require you to dig holes for posts or sonotubes.
Gradual slopes are a bit simpler, as you can backfill with gravel and build a simple retaining wall. Below we’ll go over installation options for both gradual and steeper grades.
How Will Shed be Used?
Building on a grade requires some planning. If your shed is going to see lots of use, like mine, then you’ll want to plan out an easily accessible spot for your base. This might mean building on an uneven, or steeper, grade. Also, if you plan on storing really heavy loads, like bags of cement or lots of lumber, in your shed then you might want to consider gravel or concrete pad construction, if possible.
Location of the Door and Windows
Considering where to put the door of a shed is pretty important. If you are using a shed to store your riding mower, then you are at the mercy of the grade. You’ll have to put the door on the steep side unless you want to build a ramp.
You’ll also want south-facing windows to maximize your light. Orienting your shed base to have one side face in that direction is something you should consider.
And unless you plan on running power to your shed, this will be the only light you have. Therefore, having at least one window on each side, beside the door side, is a good idea.
Is Any Approval Required?
Depending on the size of your shed, you might need a building permit from your municipality. As discussed in another article, I always recommend a building permit.
Also, check with your homeowner’s association, if necessary, to make sure your shed base and structure adhere to its rules. Nothing worse than getting complaints from the neighbors after you finish your shed project!
Foundation Options for Sheds on Slope
In this section, I’ll discuss the different options for building a shed base on a slope. Remember, be sure you know your local building codes before you start and always call before you dig!
Building Shed on a Slight Slope
Nearly every shed construction will occur over a space that has a slight slope. Most of the time it won’t be discernible. However, even the slightest slopes need to be considered, because a non-level shed structure is more prone to leaks, structural damage, or even collapse.
Gravel Pad in Box
A gravel pad in a box is exactly that – a bed of gravel within a wood box. The box serves to contain the gravel and provide a solid foundation for your shed. Typically you would use pressure-treated lumber and galvanized corner brackets to brace the corners.
This type of base is best used on a slope that features only a slight grade. Steeper grades would require lots of extra gravel, making it cost-prohibitive.
Gravel Pad with Retaining Wall
A retaining wall is used to keep the earth from collapsing onto space beside it. In our case, a retaining wall acts as one side of the box that contains a gravel base for your shed. Your wall consists of pressure-treated lumber, or blocks, that use spikes or rebar pounded into through the wall into the earth.
A gravel pad with a retaining wall is a good option for mild to moderate slopes that are too steep to use an entire wood box. You could use a raised post and beam structure, but if you need to store really heavy stuff in your shed, then you should opt for a retaining wall and gravel base.
How to Level a Shed on a Slope
A string level is your best friend when leveling a shed on a slope. If you are using gravel with a box, using stakes at each corner and attaching strings to each will help you ensure that adjacent and opposite sides and corners are level.
If leveling a pad with a retaining wall, you’ll stake out the higher end and attach a string to the bottom of the stake where the shed base abuts the ground.
How to Build a Shed Base on a Slight Slope
When building a shed on a slight slope, you’ll want to build a box and fill it with gravel. Stake out your corners and string them up. Use pressure-treated lumber to create a box.
Alternate lumber pattern to create overlap at each corner and pound rebar through lumber into the earth. Remove topsoil from within pad and put down a weed barrier. Fill with gravel and compact thoroughly.
Building a retaining wall works in the same manner, but you are only building three – or less – of the sides. The key to building a solid retaining wall with gravel is having a trench at the bottom of the pad with a weeper. This is a sleeved pipe that keeps out sediment but allows water to pass through – and it will keep your foundation dry.
Image courtesy of StorageBuildingsUnlimited
Building a Shed Foundation on a Steep Hillside
Building on a steep grade makes using a retaining wall and gravel impossible. Large volumes of gravel can be pretty expensive, not to mention the amount of lumber and length of rebar required to build a box or retaining wall. Below are some options for a shed foundation on a steep grade.
Concrete Piers and Beams
One of the more labor-intensive options, this type of shed foundation requires you to dig holes below the frost line, put in sonotubes and fill them with concrete to just above grade. Once installed, you can place your beams on top of the concrete piers.
Concrete piers are one of the strongest options for a shed, and may also be mandated by local building codes. Posts or beams sitting on top of concrete piers may need cross-bracing to ensure the stability of the box and shed above. Bracing each horizontal side of the box to a post will help keep your base from moving.
Post and Beam
Post and beam construction is similar to concrete piers, except your pressure-treated posts are buried in the ground. Posts should rest on concrete footings, which can be poured into the bottom of the holes and will level itself.
Once the posts are on concrete and you fill the holes around the post, the post should not move at all. Your beams and box rest atop the posts.
Posts buried in the ground are faster to install. However, some local building codes disallow buried posts, particularly areas in colder zones. On the other hand, post and beam construction is highly stable and doesn’t require and cross-bracing if using 6×6’ posts.
Screw piles are long metal poles with a tip that looks like a screw. There are two types: the kind you buy at a big-box retailer and the ones a contractor installs with a machine.
Contractor screw piles can be up to ten or twelve feet long and have to be professionally installed. This would be the most expensive shed base option, but also a very solid option.
You can take the DIY route and purchase screw piles to do yourself, however, these are not as long and, thus, not as strong. If you have earth that is too tough to dig through, such as clay, you might want to consider screw piles. However, be sure to get them installed to make sure they are strong enough.
How to Build a Shed Base on a Steep Slope
A steep slope requires a strong foundation. Posts in the ground can be prone to movement or moisture issues. Screw piles are expensive and, usually, impractical to use just for a shed. Concrete piers are strong, won’t budge, and won’t cost you much.
Building a pier foundation on a steep slope requires you to determine the right number of piers and their location. Dig or drill the holes and put the sonotubes in, making sure they are level and plumb. Fill them with concrete and place a galvanized post base on top.
Once the concrete sets, you can install the posts and beams. Your deck box and shed will sit on top of the beams. Make sure you have cross-bracing affixed to the box and posts, which will anchor the entire structure to the foundation base.
Creating a shed base on a hill can be a challenging task, but one of the primary considerations should be ensuring a stable and level base.
The hardest part of the whole job is likely the labor, whether it is compacting gravel or digging holes for piers. But, if done right, your base can last as long as a base on level ground.
I hope you found this article helpful. If you have any questions or feedback, please share it, below. And as always, feel free to share this article if you found it useful.
Eugene has been a DIY enthusiast for most of his life and loves being creative while inspiring creativity in others. He is passionately interested in home improvement, renovation and woodworking. A little more about me.