How to Build a Shed Base on a Slope

When building your garden shed it’s always better to place it onto even ground. However, if that’s not an option you have, there are plenty of different ways to resolve this.
Building your shed on uneven ground can cause problems in the installation process, so the easiest way to fix this is to level the shed base!
Two popular choices are foundation blocks or building a small retaining wall. Both these solutions will solve the issue of the garden building in question sitting on uneven ground.

Take a look at how both of these methods work below!

reddit house on a hill cartoon

Uneven Ground

Building a shed or other garden building can cause problems in the installation process. Uneven ground includes hills, soil, grass and anything else that isn’t considered stable and level.


The location is important; you want to find a flat secure area for your shed to be built on. If you only have uneven ground, there are ways to resolve this.

Slight Slopes

It’s possible to build your shed base on a slight slope. You can use various methods to build a level base that’s suitable for your garden building to be placed on. When looking to create a level platform, you’ll want to make everything ground level, some ways to do this include foundation blocks and retaining walls.
When you build your shed base, the easiest way to make sure 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 is too large, this is a great compromise. It involves taking a piece of string and pulling it taut against the wall or blocks that make up the boxing (or ‘edges’) or your proposed base site. The string line will give you a perfect gradient between the two points. So if the ground is too high or too low at any points you can level it.

For more advice about ground levels, you could always seek advice from a professional builder. In the mean time, take a look at how to find the best location for your garden shed.

Base On a Slope

Flat ground isn’t always an option when you’re building your shed. However, the best option is always to have your base on level ground.

Building on a slope can be done with ease if it’s done the right way. And an assessment of the ground is a great way to check the area you’re about to build your base on is an acceptable plot of land.


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

The height of foundation blocks depends on the section of your ground that is level. However, if it’s a larger slope, looking into building a retaining wall would be a better option.


Timber posts are also a very popular starting points for a retaining wall. Rather than blocks of wood, some opt to build their retaining wall using timber posts.
They’re not only used to build the retaining wall though! Timber posts can be used when building with foundation blocks to see if they’re level.


There are several different types of foundations available when levelling your base on a slope. Although pouring concrete footings are essential is constructing a base for a solid or livable structure.

A weed barrier is also a crucial item to have. After digging and levelling your uneven ground, placing a weed barrier will prevent any weeds below from making their way up to the shed above. This is important because once the base is built and any weeds come through, you won’t be able to resolve this without taking down your shed to get to the area below. They may also cause rot.

A gravel base, also known as a gravel pad, is an alternative to soil. You can either space gravel pads out along the edges of your proposed base of use an ecobase foundation and fill it with gravel or pea shingle.

A great base option is always a concrete base. It’s solid and permanent meaning your shed won’t move once it’s built. It’s also a great option if you want a base that doesn’t need any maintenance. You can build this foundation as you need to create the perfect height for you and level off any area.

Another form of base is a foundation perimeter. This involves some solid concrete on the outside section of your base creating stability and also giving protection against things like ground moisture. You can then dig out┬áthe 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.

Lumber vs Pressure-Treated Lumber

Lumber, also known as timber, can also be pressure treated. Pressure treatment involves introducing chemicals and preservatives to timber in a vacuum. This way, they penetrate much deeper than regular dip treatments or painted on wood treatment.
Lumber that isn’t pressure treated does still last, however, you will need to treat it yourself once a year to help with maintenance. In the long run, pressure-treated lumber is the better option but maintenance is still key.

Foundation Block

Foundation Blocks

Foundation blocks are a nice and easy solution to sloping ground, as you can add and remove blocks to fit the height you need.
This is a great way to create a solid foundation and you’re able to fix the height difference that you have in your space for your garden shed. It’s even a great option for steeper slopes and helps to create level ground.

Here’s what you’ll need:

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

How to Build a Level Shed Base Using Foundation Blocks

Step 1: Start by measuring out the space for your shed base. You can use posts to mark the space out and string line to keep them in line.

Step 2: Dig out the top layer to make your ground as flat as possible, leaving the soil below exposed. 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: You’ll need to dig two inches wider than the blocks and then six inches deep minimum. Fill the hole with pea gravel, this will 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 this is done and you’re sure the ground is level, you can start to build 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!

Retaining Wall

Retaining Wall

A retaining wall is a perfect solution to building on shallower slopes. For this method, you’ll be cutting into the slope and creating a level platform whilst the steeper ground is held back by the retaining wall. This is the best method for building a shed onto a steeper ground such as a hill.
This is a simple method that can be done by even amateur builders!

Here’s what you’ll need:

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

How to Build a Level Shed Base With a Retaining Wall

Step 1: Start by digging out the soil from the slope to create a flat surface, this will help to make 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.

Tip: If you’re filling it with gravel, use some filter fabric to prevent soil from falling back in.

Step 3: Consider installing a drainage pipe, this is a preventative measure that allows water to flow nicely out from the wall.

Step 4: Start to 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 if you’re considering building a large wall on a steep slope, it’s recommended you seek professional advice from an experienced builder. They can also give you advice on ground stability and your base structure.

A wall solution is a type of solution that 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.

Tips to Remember

The type of base you have is important to your garden structure. The same rules apply to log cabins and other types of outdoor buildings.

It’s best to build your shed onto a base option that’s strong and durable. If you’re ever unsure if your base area is sloped or not, just remember it’s always best to have a level base. Even slight slopes could cause issues.

The type of foundation you use is also important. A gravel or pea gravel foundation is great as are both a retaining wall and foundation blocks. They can all help keep the ground below compact and keep your foundation level. Both a gravel foundation and pea gravel are durable foundations. Perfect for you to use!

Extra Tips!

  • 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.
  • Remember to check with your local authority about any planning regulations. It’s best to do this before work starts to ensure you’re not breaking any planning laws or building regulations. This will also help to check if you need a building permit.

And once you’ve got your slope levelled or built up you can shop from our range of wooden sheds via the button below!

Shop Apex Workshops


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!