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By Amy Hanlon on 05 Jun 2024

Does a Garden Shed Need A Concrete Base?

A good shed starts with a good base. But is concrete the best choice for a shed base? Let’s look at your options so you can decide which is best for your garden.

Why does my shed need a base?

A level, stable base is essential for keeping your building square and solid. Without a firm foundation, a shed will sink into the ground underneath, and it’s unlikely to sink on the level. 

Once your shed base is no longer level, neither is the building. All the precise angles that make up the walls, roof and doors aren’t precise anymore. As a result, the doors won’t close or open. Joints start failing. Timber starts moving. Water gets in.

It’s like trying to build a tower of blocks on a wonky tabletop. Without a level base that stays level, your building won’t stay square, and just like the wobbly blocks, your dreams of a perfect shedlife come crashing down.

Can I put my shed down on breeze blocks?

Shed bearers laid on breeze blocks, sitting on a compacted hardcore base. The base is surrounded by a grey wooden fence.

There are lots of different solutions to the problem of keeping your building level and square. It’s difficult to give a one-size-fits-all answer because there are several factors which may or may not contribute to the right solution for you.

For example, putting sheds on a breeze block base can be a solution, but it isn’t always the best solution. It very much depends on the ground underneath the blocks.

If you use breeze blocks, then bearers, lay your shed floor on top of the bearers and build up from here, you distribute the weight of the building evenly over the ground under the blocks. Because of this even distribution, the building is less likely to sink.

However, if some of your breeze blocks are on solid ground, and some are on wetter, softer ground, the weight of your shed and its contents will still cause subsidence at the weaker points. As long as you’re aware that this may happen, a breeze block base could be just what you need. However, if you’re looking for a shed that’s got some serious staying power, there are better alternatives.

Depending on the quality of the ground underneath your shed, breeze blocks can form a suitable base, but they’re no substitute for a slabbed or concrete base.

Are slabs a good base for a garden shed?

A level slabbed base for a 12' x 8' shed, surrounded by gravel and with grass in the background.

We recommend a slabbed base for a garden shed. However, just like breeze blocks, slabs can’t simply be laid on the ground underneath. If there’s any discrepancy in the quality of the ground, you’ll still end up with a sinking shed. 

A slabbed base should have a solid sub-base, like this:

A compacted hardcore base ready for slabs to be laid on top. the base is surrounded by cobble stones, and a hedge is visible behind it.

To avoid any problems with soft or inconsistent ground under your building, a good base replaces that ground with material solid enough to support your building, namely type 1 hardcore.

To construct a brilliant base you should:

  1. Dig down at least 4-6 inches (sometimes even deeper) until you reach solid ground.
  2. Fill in the area you’ve dug out with Type 1 hardcore. Level and compact the hardcore.
  3. Lay your mortar and slabs on top of this sub-base.

Type 1 Hardcore is sometimes known as Type 1 MOT – the MOT stands for Ministry of Transport, and this aggregate meets the standards set out by the ministry for the construction of roads. If it’s good enough for a motorway, it’s good enough for your shed!

Can I use ground screws as a base for my shed?

A timber base frame on a ground screws base.

Another option for a shed base is ground screws. As the name suggests, this involves screwing large metal screws into the ground. Ground screws are a great option for hard-to-reach or sloping sites. They’re less invasive than concrete and are often more affordable than slabs.

However, be aware that the additional height of a ground screw base can raise your building considerably. This may mean that you’ll need planning permission.

It’s also worth remembering that not all sites are suitable for ground screws – check with your contractor to make sure that this option is available for you. 

When do I need a concrete base?

A poured concrete plinth for a timber garden building, next to a house and a fence. In the background is a lake and hills.

A slabbed base is more than suitable for a garden shed. Because of the costs associated with laying a concrete base, most people are delighted to find that this isn’t necessary.

However, you will need a concrete plinth for larger, heavier buildings, like our Blackstone Garden Rooms. Depending on design, you may need a concrete base to bolt the building to, but this would generally only apply to much larger structures, like Garages.

Does a garden shed need a concrete base?

If your heart is set on putting your garden shed on a concrete base, there’s no reason not to. However, it’s not necessary. Slabs or ground screws are more than adequate, and these are what we recommend for our Pent and Apex Sheds.

Our Learning Centre is a wealth of knowledge on all things base-related. Take a look if you need more information. Or if you’re ready to get your Shed project off the ground, why not book a Consultation with one of our Team? This is your chance to ask all the questions you like about your Shed plans and get answers from an expert.

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