How To

How to actually build a sturdy shed foundation for your beautiful garden

By Luke Carlino

Updated: July 1st, 2021

Every good shed starts with an even better foundation.

Everyone (with a garden) needs a good garden shed. This very useful space is great for extra storage or a place to craft other various projects, but every good shed starts with a solid foundation. You want to ensure that your garden shed offers stability and safety, and learning how to build a shed foundation is the path to achieving that.

It should also be noted that whether you are building your shed from scratch, or buying a pre-fabricated option, both methods require you to form the foundation. This makes learning how to build a shed foundation an unavoidable step for anyone who wants a new shed.

Read on for all of the essential steps to ensure the correct surface, along with the steps for how to build a shed foundation.

Start by levelling the surface

You have a few options for your foundation, be it concrete, a raised wooden deck or concrete slabs, but all will require that you start with a level surface. Your shed will probably warp over time, and the adverse effects of this will be lessened if you level the ground first. Remove the debris and place a weed-proof membrane down to prevent things from growing through the floor.

Grass and weeds growing under your shed can be a problem as the floor will not dry out properly after the rain. This can cause premature rot, mould and mildew.

Laying the base

There are many base options for your shed, but the most popular are cast concrete or concrete paving slabs. Both options provide a longer-lasting garden shed foundation, and will require these steps:

  1. Use mason’s string and batter boards as a border around the area
  2. Dig about 15 cm deep 
  3. Place a wooden framework for the concrete 
  4. Place a level layer of 7 cm deep gravel, then pour the mixture of cement and concrete
  5. Spread out with a hand screed
  6. Let it dry completely starting the shed

Make sure you have all the tools and materials before you start to make for a more efficient process. While this is a task that is made easier with two people, it most certainly can be done with just one.

Common mistakes to avoid

The first thing to avoid is laying paving slabs on irregularly spread gravel as this will create an unstable base that will warp and crack over the years. Your base will likely sink once the underlying material disintegrates.

If opting for a raised wooden deck, ensure you clear the ground first and use a weed-proof membrane. While ideally, you’ll find a spot that is already level, you can still learn how to build a shed foundation on uneven ground. This will require grading the soil and making sure you are not in a spot that will collect water.

If you want to ensure that your base area stays dry, remove all grass from the site and use a dirt tamper with 5-6 cm of gravel to help drain the water underneath. Knowing how to build a gravel foundation for a shed will help secure the longevity of your base when it is up against the elements.

building a shed foundation
Source: Shutterstock

How to build a shed foundation with deck blocks

Deck blocks are another option for your shed foundation. These pre-formed masses of concrete feature formations in the top to hold vertical posts or beams. Many people prefer this feature as a form of extra structure security.

While they are generally a more temporary foundation for freestanding or floating structures, many people use them as they have a more straightforward installation process. You should not consider the option, however, if you are in a high wind area. Your local building code office will usually have the final say on whether or not you can use them.

Deck blocks are quicker and cheaper to install and require minimal surface prep or digging. The number of blocks you need will depend on the weight, layout, and size of your shed. The bigger the shed, the bigger your blocks. You will likely need help moving larger ones into place as they can be weighty.

The steps for building a shed foundation with deck blocks

First, you’ll want to level your blocks and ensure you have the following tools on-hand:

  • Tape Measure
  • Mason Line
  • Level
  • Safety Glasses
  • Knee Pads
  • Laser Level

1: Calculate where your blocks will be located and prepare the area with level string lines

2: Place your blocks in position and continually check to ensure your structure is level 

3: Measure diagonals to make sure all blocks are in the correct position. 

While deck blocks can be a very stable base, they can be challenging to level if the ground settles once the shed is built. Try to avoid disturbing the environment too much while levelling the deck blocks.

What happens if I have no or inadequate foundation?

Apart from being unsafe, a shed that is not level won’t look very good or feel great to be inside of. Doors and windows may not close properly as your shed will settle over time, causing things to come out of alignment. Avoid this right from the start with a solid foundation.

You may also find that the centre of the floor may not be well supported, primarily if you use concrete blocks on an uneven base. If the centre of the floor is inadequately supported, it will result in a bouncy floor that sags over time. This is especially the case in a larger shed or garage that will be storing heavy vehicles or equipment.

open garden shed with gardening tools
Source: Shutterstock

Frequently asked questions

What is the best foundation for a shed?

You have a few options for your foundation, most commonly concrete, a raised wooden deck or concrete slabs. The most popular options can be cast concrete or concrete paving slabs. They will provide a longer-lasting garden shed foundation. Wooden decking is a popular option as it looks neater and easier to level. If you do opt for this, however, ensure that you lay a weed membrane beneath it to prevent various growth through your deck.

Ultimately, the decision will be based on whichever aesthetics you prefer, or the foundation that is within your budget.

Do you need a foundation for a shed?

Absolutely! Whether you are building your shed from scratch or buying a pre-fabricated option, both methods require you to form a foundation. This makes learning how to build a shed foundation an unavoidable step for anyone who wants to build a new shed. The foundation will help ensure your shed’s longevity as it battles the outdoor elements.

The quality of your foundation will also help you avoid other issues. Besides poor aesthetics, shed doors may not close properly on an unstable base. You may also have drainage issues, or problems with wet areas underneath your shed if the flooring has not been treated properly.

How do you prepare a foundation for a shed?

Once you have decided what your shed foundation will be (most commonly concrete, a raised wooden deck or concrete slabs), you’ll need to level a surface. This is a crucial step to ensuring the longevity of your base, so remove the debris and place a weed-proof membrane down. This will prevent things from growing through the floor.

If you have opted for a cast concrete or concrete paving slab base, use mason’s string and batter boards to form a border around the area. Dig about 15 cm down placing a wooden framework on the edge for the concrete to then be poured into. Add a level layer of 7 cm deep gravel, then pour the mixture of cement and concrete in, spreading it out with a hand screed. Allow it to dry completely before you start work on building the shed on top.

Enjoy the peace of mind in knowing your shed will stay up!

Now that you’ve learned how to build a shed foundation, you can push on with the rest of the shed knowing that it won’t collapse! We’re sure you’ll undoubtedly appreciate that peace of mind when standing inside of it. Safety first, always!

If you’ve mastered the foundation but are having a little trouble with the shed installation, there are plenty of Taskers on hand to help! You’ll find people who are specific experts in Bunnings shed installation, or the building of various other garden shed designs to ensure you have a quality space that will perform its function for many years to come. If you already have a shed, but it is in some drastic need of repair, we have the people to help with that as well.

If, on the other hand, the successful laying of your shed foundation was understandably satisfying, have a read of our backyard ideas blog and proceed with building the shed yourself. These blogs will give you some other great DIY projects! It will not only increase the value of your home, but also the function and enjoyment of your outdoor areas. Grab the tools and get to work and make your backyard something you are proud of today!

ABOUT THE AUTHOR

Luke Carlino

Luke Carlino is a freelance copywriter, social media manager and content creator based in Melbourne. He works for a range of clients across a plethora of industries and is also an accomplished musician with solo and band works online.

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