How to Build a Shed Base on a Slope

A level base, paired with a solid foundation, is where your garden shed deserves to be. But if that’s not an option you have, don’t panic!

Not all garden plots are perfectly levelled. Chances are, you’ll have to deal with a slope one way or another when building a shed. However, positioning outdoor buildings on an uneven surface doesn’t guarantee a successful installation.

The good thing is that there are plenty of ways to resolve this. The easiest solution is levelling the base itself and installing a strong foundation.

Two popular choices are foundation blocks or a small retaining wall solution. But either way will solve the issue of the shed in question sitting on uneven ground. Take a look at how both of these methods work below!

Importance of Level Base for Garden Buildings

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Why does the base of a shed have to be levelled? For one, the doors need to be so for all the bolts and locks to line up correctly. Building it on a not-so-level ground will cause the frame to twist and make the opening of doors and windows tricky.

Second, most sheds, such as wood types, are the heaviest on the market. Thus, a decent foundation level is crucial to bear the structure’s weight. All in all, your shed won’t last long without a level and solid base.

A sloped plot isn’t much of a problem as long as the base on top of it is a level surface. This may sound demanding if you’re doing it yourself, but with planning, you can get started next weekend!

Building a Base on an Uneven Ground

When preparing the base, it should be bigger than your shed. But before you finalise the footer requirements, there are a few things to consider:

1. Location

Shed base foundation near the backyard's fencing

(Image Credit: Felix Wong)

The location is important, and thus find a flat secure area for your shed. If you don’t have a completely level ground to be built on, you can use various methods: 1.) building on a slight slope, 2.) foundation on steeper slopes.

2. Assess the sloped ground

Sloped backyard

(Image Credit: Living in Dryden)

Flat ground isn’t always an option, but building on a slope can be done with ease if done the right way. Assess the ground to check the area and see if it’s an acceptable plot of land.

The easiest way to ensure it’s straight is to use a string level, also known as a string line. If you can’t get access to a spirit level or the area to check it’s too large, this is a great compromise.

The said tool involves taking a piece of string and pulling it taut against the wall or blocks. This makes up the boxing or ‘edges’ or your proposed base site. The string guides will also give you a perfect gradient between two points. If the ground is too high or too low, you can level it.

Always seek advice from a professional for more ground level tips.

3. Height

When building a retaining wall, there’s a restriction on height. If the braced wall is going to be over 1 metre tall, you’ll require planning permission.

Foundation blocks, in contrast, will depend on the section of your levelled ground. But if it’s a larger slope, looking into building a retaining wall would be a better option.

4. Posts

Timber posts are also a more popular starting point for a retaining wall than wood blocks. They’re not only used to build the retaining wall, though! A timber post is also ideal for building with foundation blocks to see if they’re level.

5. Foundation type

Small shed foundation

(Image Credit: Flickr)

There are several types of foundation for sheds when levelling your base on a slope. A weed barrier against a foundation makes a great example.

After levelling your uneven ground, place the weed membrane on top. This will prevent pesky weeds from making their way up to the shed. Once the base is built, any greens to sprout through will be hard to remove and may also cause rot.

A gravel foundation, also known as a gravel pad, is also a good alternative to soil. You have two ways to work with the bed of gravel. You can space the pads out along the edges of your proposed use. Or use an eco-based foundation and fill it with pea gravel.

Another form of base is a foundation perimeter. It involves some solid concrete on the outside section of the base. This creates stability and also gives protection against things like ground moisture.

You can then dig out the foundation inside and fill this with soil or gravel, as mentioned above. It’s a built-up foundation that can suit whatever height you need.

But when talking about the best base option, you can never go wrong with a concrete foundation. It’s solid and permanent, meaning your shed won’t move once it’s built. Not to mention it’s low maintenance!

How to Build a Level Shed Base Using Foundation Blocks

Foundation blocks

(Image Credit: Flickr)

Foundation blocks are a nice and easy solution to sloping ground. You can add and remove blocks to fit the height you need. It’s even a great option for steeper slopes and helps to create a level ground.

Here’s what you’ll need:

  • Masonry blocks
  • Measuring tape
  • Spade
  • Treated timber planks
  • Marking posts
  • Pea gravel

Step 1

Start by measuring out the space for your shed base. You can use wooden posts to mark the space out and string lines to keep them in line.

Step 2

Dig out the top layer to make your ground as flat as possible, exposing the soil below. Make sure to clear the excess soil and measure out four rows of blocks. Doing this will help to keep an even distribution of weight.

Step 3

Dig two inches wider than the blocks and then six inches deep minimum. Fill the hole with pea gravel to even out the surface and create a flat space for you to work with.

Step 4

Place your timber planks along the blocks you’ve placed. Take a level to them. This will help to determine how flat they are. If needed, you can always add or remove the concrete blocks.

Step 5

Once the ground is well-levelled, begin building your shed base on top. Starting from one side, screw the base on top of the timber panels. You’ve now got a sturdy base for your shed to be built onto!

How to Build a Level Shed Base With a Retaining Wall

Retaining wall foundation

(Image Credit: Flickr)

A retaining wall is best on shallow slopes, such as a hill. For this method, you’ll be cutting into the slope and creating a level platform. Do both while the retaining wall holds back the steeper ground. Even amateur builders can do this!

Here’s what you’ll need:

  • Shovel
  • Wheelbarrow
  • Buildings bricks or blocks
  • Cement
  • Wall solution

Step 1

Start by digging out the soil from the slope to create a flat surface, making the ground level. You can then balance where you’ve cut and fill it using the extra dirt you’ve dug out. This will help build the platform for the shed.

Step 2

Compact the soil or use gravel to create a level platform. If you’re using gravel, this will also need to be compacted. Top tip: If you’re filling it with gravel, use some filter fabric to prevent soil from falling back in.

Step 3

Consider installing additional drainage pipes. Doing so makes a great preventative measure that allows water to flow nicely out from the wall.

Step 4

Build your wall. You can use string to run along the side of the blocks to make sure you’re creating a straight line.

If you’re looking to create wall designs or considering building a large wall, ask a professional. They can also give you advice on ground stability and your base structure.

A wall solution helps to damp-proof a wall. This stops water from damaging the wall you’ve built, which could result in the wall falling down in the long run. A drainage pipe will also help with this.

Top tip: Place your shed at a distance away from the retaining wall. This will help you to walk around your shed when needed and create access for people to maintain all sides.


The type of base you have is important to your garden structure. The same rules apply to log cabins and other types, including summer houses.

The type of shed base or foundation you use is also important. For one, gravel or pea gravel is great for retaining walls and foundation blocks. Not only can they help keep the ground below compact, but they also maintain the foundation level.

Always check with your local authority about any planning regulations. Doing this before work starts is best to ensure you’re not breaking any planning laws or building codes. This will also help to check if you need a building permit.

If you’re ever unsure if your base area is sloped, it’s always best to have your garden shed in a levelled base! Our guide to building a shed base is a great reference, particularly if you’re new to this approach.

Quick question: When relocating your outdoor structure, how close can it be to the fence?

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Yes, as level as you can get it. Without a level base, you could face problems installing your garden shed.

Yes but this will require excavation and either foundation blocks or a retaining wall. Foundations blocks are great for a steep slope whilst a retaining wall is best for shallower slopes.

Building a shed on an unlevel ground or undisturbed ground can cause you to be unable to build your shed properly.

The roof may not sit right whilst the timber may start to crack. Always make sure you have a level base and on a strong foundation!