How To Build A Concrete Shed Base

Building A Concrete Shed Base

Preparing and building a stable base for your garden shed is vital to ensure your shed is completely level and secure. In this blog, we will explain the key points about building a base from concrete and the steps that you will need to take to build one.

Do I need a base for my shed?

We are frequently asked this question and the honest answer is that all garden buildings need a high quality, properly constructed base. Otherwise, your new garden shed will be hard to assemble, difficult to align correctly and will inevitably rot and sag due to water penetration.

There are multiple choices when it comes to materials for your foundations, however, we would recommend concrete for ensuring your shed is set up for a long life. See our rundown of installing other bases in our help centre here.

Your shed base should be solid, square, level and of the correct size. Additionally, you will need to consider things such as having enough room to get around the shed during assembly and maintenance. It’s important to consider cutting back on surrounding vegetation, such as overhanging trees or bushes to prevent future problems caused by friction when installing your base.

Before laying down the foundations of your base, we recommend considering what your shed will be used for to factor in choices such as sunlight, a view of the garden, electricity or water supply, if desired. If you’re stuck for inspiration for shed use take at look ways you can transform your shed.

We advise that a shed base should be fractionally smaller than the shed footprint and elevate the shed off the ground.  A slightly smaller shed base ensures that driving rain will run down the side of the shed and drip clear of the base. It also prevents water pooling and running under the base.

For example: If your shed’s footprint is 3000mm x 2400mm you would then subtract 10mm from both dimensions giving 2990mm x 2390mm. Remember to always check the footprint size with the manufacturer before starting your shed base.

How much concrete will I need?

Whether you’re buying ready-mixed concrete or mixing your own with ballast and cement, concrete is typically measured in cubic metres.

There is a simple equation for working this out;

Length x Width x Depth

For example, a base of 3m x 2.4m with 100mm depth (75mm – 100mm is a good depth for most sheds), the calculation would be 3 x 2.4 x 0.10 =  0.72 cubic metres.

We’d always recommend adding an extra 10% to your result as a “just in case”. Its always better to have some left over rather than run out.

What tools will I need?

We recommend getting prepared with the appropriate tools before starting on your concrete base. Here’s our list of recommendations:

  • Tape measure
  • Pegs and string
  • Spirit level
  • Set Square
  • Spade
  • Shovel
  • Rake
  • Cement mixer
  • Wheelbarrow
  • Concrete tamper or levelling beam
  • Vibration plate
  • Timber (length and depth of your base)

How do I build a concrete shed base?

The next consideration is the method of construction. There are many ways to construct a shed base but no matter the method you choose, it needs to be high standard. If you are not confident about tackling it then we recommend employing a reputable builder.  A garden building will not stand truly vertical if the base isn’t level. For a sound footing, we would suggest using concrete, slabs or paving stones.

Concrete makes the strongest most durable shed base, especially when it is reinforced. It is suitable as a base for all types of garden building; however, it is expensive, time-consuming to lay and permanent, so you need to get it right first time.

Follow these steps to install your concrete shed based correctly:

Step 1 – Choose your location

Select the location for your new shed. Keep in mind your requirements, if you’re erecting a potting shed, you will want to consider shade and natural light. If you are wanting to install electricity, you’ll need to consider when the mains supply is.

Once you’ve chosen your location, roughly mark out the area and remove the turf. Dig down until you find firm ground.

Step 2 – Measure our your base

Accurately measure and mark out your base dimensions with wooden pegs and string. A good way to check your dimensions are even is to measure across diagonally, if they are the same, then your sides are even.

Make sure any overhanging trees and bushes are cut back to allow at least a foot around the actual base.

Step 3 – Lay hardcore and level

If your subsoil is not of a firm and dry consistency, put a layer of hardcore down and leave enough depth for the concrete to go on top (about 50mm). About half of the depth of your base should be above ground level.

For a general garden shed a 75mm bed is sufficient in most situations on soft clay. For larger buildings, make the thickness of the base 100mm.

Make sure that you break up and compact the hardcore well. Use a vibration plate if necessary.

Ensure you have a clear, level ground (check out our guide to building on uneven ground).

Step 4 – Create the timber frame

Using your string markers, lay your timber frame.

Before nailing/screwing to your pegs, ensure the frame is level.

Where possible, make sure the pegs do not protrude the tops of the frame, as this will make levelling the concrete more difficult.

Step 5 – Mix the concrete

If possible mix the concrete alongside the base, this makes the placement of the concrete far easier, a wheelbarrow may come in handy for this step.

Remember: Always follow the manufacturers guide for making your cement mix.

If you’re making your own, the ballast and cement ratio of 5:1 is typically the recommended choice.

While mixing the concrete, add the water gradually to the mix until the whole pile is uniform in colour and sufficiently workable to use. Do not make the mix too wet as this will weaken the concrete. Make a note on how much concrete has been used and use the same for each mix thereafter.

Step 6 – Pour the concrete

Pour the concrete into the frame and ‘tamp off’. This is the process of compressing the mix to remove all of the air bubbles.

Tapping the sides and corners of the frame will help the concrete settle and have a solid edge to the slab.

Continue this process until the frame is filled.

Use a levelling beam or tamper to work from one end of the base to the other, ensuring everything is flush and level with the frame.

Step 7 – Let it set

You should leave the base to set for at least 3 days before the frame is removed.

If the weather is wet or very cold, it will likely take longer to set, if this is the case, we recommend covering your base with a plastic sheet.

Don’t let your base dry out too quickly in warmer weather as your base will start to crack. To prevent this, spray with water for several days.

Once your base is ready, remove the timber frame and await your new garden shed.

Still have questions?

We hope you have found this article helpful – if you have any other questions or would like our advice about choosing the right shed for your needs, then do get in touch.

Request a quotation or call our sales manager, Kevin on 01405 765400

About Sheds Direct

We build quality garden sheds, Dutch barns, workshops and summerhouses.  All of our sheds are built to last, we use quality materials, thicker tantalised wood framings for solid structures.

Whether you’re wanting a shed for storage, to work in or as a relaxing space, you can be sure all of our products are premium made, of quality materials and will look fantastic.

Sheds Direct manufactured by us in Britain, and erected in your back garden. We are so passionate about what we do and its really important that we deliver the best products we can at a great price. But don’t just take our word for it – check out our Facebook and Google for testimonials by our customers.

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