shed base on a slope stone finish

How to build a shed base on uneven ground

Finding the perfect location for your shed can be tricky, especially when your garden landscape is on a slope, has an uneven surface or has different elevations. In this post, I’m going to show you how to build a secure shed base that can be used on almost any uneven garden surface. I recently built a garden office on an uneven surface in my garden so I can show you exactly how I achieved this. I’ll also talk through some other techniques that will provide a really sturdy foundation for your shed.

There are two main garden-building base types that could be used for this type of project:

  • A wooden frame base
  • A solid base made from concrete or patio slabs

The solid style base will require a fair bit of groundwork, a sub-base and a finishing base from poured concrete or laid slabs. You could also opt to build your shed directly onto the sub-base which can be good for drainage. To tidy things up, a layer of nicer-looking stones can be placed on top to finish the base.

shed base on a slope stone finish

In some cases, you might need to build a retaining wall to support the earth from shifting. I will go into more detail about this below.

Talk a look at my DIY shed build for some more foundation ideas and inspiration for a shed build of your own. Building your own shed can save you money, is more fun and it will look much nicer than a flat pack shed.

To kick things off I’m going to take you through step-by-step how to build a wooden frame shed base.

Building a wooden frame shed base on a slope

This is a very effective way to build a base for your shed or any other type of garden building. It’s how I built a sturdy base for my log cabin/garden office.

I wasn’t dealing with a steep slope but the ground was very uneven. Our garden inclines away from the house and then drops down at the back, leaving a small hill which I had to build on. To avoid loads of groundwork I decided to build a sturdy wooden frame base. Here is how I did this.

building a shed base on uneven ground

As you can see the rear of this base is lifted off the ground. I had to dig into the front section slightly and raise the rear by about 60cm.

shed base footing post

Using 100x100mm fence posts and 150x47mm construction timber you can create this level platform.

  • Clear the area of debris.
  • Measure your area and mark it with spray paint, chalk or string.
  • Place your timber edges to mark the area and work out where the corner posts will be located.
  • Dig holes 300x300mm and 600mm deep in the ground. If the ground is very soft then dig a little deeper.
  • Place 50mm of stones in the bottom.
  • Pour 30mm of cement on top of the stones. Leave to set.
  • Place 100x100m fence posts into the hole and fill it with cement. Ensure the cement fills the hole above ground level. Before the cement dries, level the posts using a spirit level.
  • Treat the remaining wood post with creosote to prevent rot.
  • Attach the outer frame to the support posts using 80mm (5mm diameter) wood screws.
  • Fix the inner frame.

No part of the shed frame should be touching the ground. Larger frames will require more support posts. Here is an example of a 3600x4200mm frame.

wooden shed base build on a slope

A shed base of this type can be constructed on most uneven surfaces including steep slopes.

Here’s an example of the holes I dug for my support posts.

Alternative footing method for a wooden frame base

Here’s a great alternative footing method for your garden shed base.

Concrete footing and post anchor

post footing amazon

Concrete footings similar to those above can be poured into moulds and a post anchor can be set into the top. You can then mount the wooden frame to the post anchor which will keep the frame dry and free from rot.

The concrete can be set into a mould made from wood, plastic or strong cardboard tubes. Many people have used cheap buckets, cardboard postage tubes (cut to size) and a square wooden frame mould for this purpose.

Here are a few options for post anchors.

Building a patio or concrete shed base on a slope

The foundations (or sub-base) of the shed will require a flat, level surface which normally means groundwork will need to take place. Levelling a slope can be tricky depending on the slope incline. If you have a steady slope, you should be able to simply dig into the higher section and move the soil to the lower section.

By adding a MOT type 1 sub-base you strengthen the base enough to then lay patio slabs or pour concrete. The sub-base should be compacted with a wacker plate (aka vibrating plate or compactor) to ensure it is sturdy and does not move over time. You can then lay patio slabs directly onto this base or pour a cement mix and level.

A layer of sharp sand can then be added to the surface making it ideal to lay slabs. The wacker plate will help compact the sub-base, strengthening it enough to support the weight of a shed and it’s contents.

compactor on sand base

Building a shed base on a steeper slope

In most cases, a retaining wall will be needed to hold the load of the soil above the levelled area and support the base. A foundation should be dug and concrete poured to hold the wall securely.

retaining wall on slope

A single-skin brick wall alone won’t be enough to hold the load on a steep slope but there are ways to strengthen this.

Building a retaining wall for your shed base

Reinforced concrete bricks

A reinforcing steel bar can be used to support hollow concrete blocks. The lower level of the wall can be double-thickness blocks and steel can be inserted into the blocks to strengthen the wall.

steel rod inside hollow concrete block
hollow concrete brick wall

Oak sleepers / Railway sleepers

A retaining wall can also be made up of oak sleepers. This is a well-known method for building a retaining wall between 30 and 90cm tall. Old or new sleepers are great for this job as they are big and extremely heavy. They can be cut to size easily and placed in a shape and size to suit your requirements.

oak railway sleeper retaining wall

The sleepers can be laid flat and screwed together or you can dig them into the ground upright as in the above picture.

A leaning or curved concrete brick wall

A retaining wall constructed on concrete bricks can be layered and leaned into a slope to provide a good brace. Likewise, a curved wall will provide a strong structure to keep the soil behind it secure.

rounded retaining wall

In the above picture the bricks can simply be glued together using a suitable masonry adhesive. For smaller walls with less mass behind them this can be the ideal solution which also looks great.

Gabion cage

Using a gabion cage can be a great way to build a solid retaining wall. It’s relatively cost-effective and an easy DIY project. With the groundwork complete you can place the cage and fill it with stones of your choice.

gabion stones

Gabion cages come in many different styles, shapes and sizes so you should find something suitable for your specific needs.

Brick retaining wall

A brick retaining wall is a very popular choice but not really a DIY option unless you have experience laying bricks. These walls can be complicated and time-consuming to build but look great. If you want your retaining wall to look great as well as function well then seek to hire a professional for this job.

brick retaining wall

Rocky retaining wall

Perhaps the cheapest method if your garden isn’t on a very steep slope. By placing a number of large rocks at the foot of the retaining wall you can prevent landslides onto your shed. Equally, if you can get your hands on some chunks of slate you can build a loose retaining wall.

slate garden retaining wall

Landscaping and excavating your plot

Moving large amounts of soil, dirt and earth will require an excavator in most cases. This can be tricky in a back garden with limited access. Luckily, mini excavators will fit through gaps less than 74cm which is ideal for going through doorways and alleyways. With this slim width and a sharp turning circle, they can pretty much fit anywhere a person can. You can hire one for about £160 per day or £320 a week.

mini excavator soil

If you like the idea of a good workout then you can tackle this job by hand. A shovel and wheelbarrow will be required and a lot of patience.

Building restrictions, regulations and planning permission for a shed or garden building (UK)

Before you get started, you should be aware of planning permission and the restrictions that will prevent you from building your shed and shed base anywhere. In most cases you will want to stay within what is considered permitted development, meaning your structure will not require planning permission.

There are a lot of controversies and misunderstandings around this subject, especially around the height at which the base can be off the ground. When you visit the Governments planning portal it stipulates that a raised platform must not be more than 30cm from the ground. Now obviously this will be complicated when working on a sloped landscape. One side/end of the base will be raised off the ground and the other won’t. So what is the correct rule and how high can you build the platform?

Some argue that the height should be taken from the back of the house but this isn’t the case.

After much research on the subject, this is what I have found.

You can read the full guide here: https://www.gov.uk/government/publications/permitted-development-rights-for-householders-technical-guidance

“Height” – references to height (for example, the heights of the eaves on a house
extension) is the height measured from ground level. (Note, ground level is the surface of
the ground immediately adjacent to the building in question, and would not include any
addition laid on top of the ground such as decking. Where ground level is not uniform (for
example if the ground is sloping), then the ground level is the highest part of the surface of
the ground next to the building.)

https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/830643/190910_Tech_Guide_for_publishing.pdf

And building is defined as:

“Building” – includes any part of a building and includes any structure or erection, but does
not include mechanical plant or machinery or gates, fences, walls, or other means of
enclosure.

https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/830643/190910_Tech_Guide_for_publishing.pdf

Therefore it is clear that the measurement should be taken at the highest point immediately adjacent to the shed base.

Whilst this is clearly defined within the government’s own guidelines, many councils will have their own interpretations and understanding of this rule, or not fully understand them themselves. It depends on who you talk to.

The best way to approach this is to:

  • Talk to your neighbours. How does your shed construction impact them? Maybe it doesn’t bother them at all. Maybe you can come to an agreement as to the best location or angle for positioning your shed. In most cases, if your neighbours know what your doing they have the opportunity to discuss any concerns and will be happy for you to go ahead.
  • Involve your local planning officer. Ask for their opinion on the matter and make sure everything is above board before you start. This could create complications but at least you know your building is within permitted development and signed off by an official.
  • Always be courteous and considerate to neighbours and council officers and should you ever have any problems regarding your structure you can always refer back to the above document. In most cases, there won’t be a problem. As long as it doesn’t upset anyone or take the piss then you should be fine.

If you just want to be on the safe side and apply for planning permission it will cost you £206 for any garden building.

What is the best shed foundation for uneven ground?

I have listed two key ways in which you can build a suitable shed base for your uneven garden. But which is the best? let’s take a quick look at the pros and cons of each type of shed base.

Wooden frame shed base

A wooden frame base won’t last as long as a solid base as wood is susceptible to weather and will rot over time. We can prolong the life of our wooden frame and shed with proper installation and annual treatment but it will never outlive a solid foundation. Wooden frames are also generally cheaper and easier to install. Materials will be easier to manoeuvre onto the site and the frame can be constructed within a day or two.

Making sure you use treated timber is essential and will add years of life to a frame. Ensure you cover the frame well to protect it from moisture and add further treatment like paint or oil once it’s in place. these small additional costs will help you get the best life out of a wooden frame base.

Solid shed base

A solid base and sub-base is a great approach if you have the time, resources and money. It should be the chosen method if you are planning to stay in your house for a long time. This base will provide a strong platform for your shed and will be less intrusive on your land, due to the fact that you will be digging into the landscape to create a level surface. Rather than it sticking out from the highest point as a wooden frame will.

Yes, it will be expensive to hire the equipment but without it, you will spend hours moving dirt around by hand. Think carefully about access to your garden. In most cases, a mini excavator will fit but measure up first to ensure you’re not wasting your money.

Consider all the materials you will need for the sub-base and how these will be moved to the site of your shed. If you’re on a steep slope you might need specialised equipment to move heavy bags of stones. Or maybe you will need to wheel it into place with a wheelbarrow. All these factors should be considered before you get started.

Conclusion

These shed base ideas son’t just apply to sheds. You can build anything on them including summer houses, garden offices and log cabins. My garden office and gym was a great project and has added a fair nit of value to our property. I treat the wood regularly with a coat of paint and check yearly for any issues in the wooden frame. With this I hope to have a garden building that will last 20 years or more.

Thanks for reading. Take a look at some of my other garden building and home DIY projects.

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