What Size Garden Shed Slab Do I Need To Lay?

What Size Garden Shed Slab Do I Need To Lay?


‘What size garden shed slab do I need to lay?’ is a very common question we get and a very important one.

Most manufacturers recommend concrete slabs as your shed’s foundation as it’s the most solid and reliable option. Although, there are other options if you can’t lay such a permanent foundation which we discuss in our article  Alternative Flooring Options for Garden Sheds.

A common mistake is not doing your research before laying the concrete slab.

This is a BIG mistake which could cost you. If you get the dimensions wrong it can be a nightmare to have to change and start your slab again (and expensive!).

So it’s a good thing you are reading this page.

Id love to provide you a chart with the exact measurements or a formula to choose however the inaccuracies of both could cause you more problems than solutions. So on this page, I want to provide you with some important tips regarding the size of the slab you should lay.

DIY or Hire A Concreter?

This is the first question you should ask before considering laying a slab for your shed.

We also recommend hiring a concreter unless you have previous experience or confidence with DIY projects. It’s not something you want to get wrong.

There are many concreters or hired professionals who can probably do the job fast and efficiently for you.

However, if you do want to take on the challenge, make sure you plan it and take no shortcuts.

Before You Lay Your Concrete Slab Tips:

If you haven’t poured a slab before, make sure to research it.

  1. First, find the shed you want before you lay the slab, don’t assume.
  2. Ask the retailer directly for slab dimensions specific to the shed you are after.
  3. Check your manual if you have already received your shed.

We have a neat video you can watch below:

Dimensions Expectations

Generally, you think to pour the concrete slab the same as the dimensions of the shed, however, brands and engineering plans may have different requirements. Mainly it’s due to getting the accurate dimensions of the model you are after.

Don’t make assumptions. When looking around online, many shed manufacturers have sizes for their sheds listed at a certain size, some companies use approximate sizing.

This doesn’t mean they are very inaccurate but it may be a few cms or so.

So it’s important to check with your retailer for exact sizing if they are using approximate measurements.

At Cheap Sheds, we try and provide the most accurate information as possible provided by the suppliers. That being said, where practical, take precautions to ensure the first step of laying a slab is correct- the measurements.

How Thick Should It Be?

This is actually not a case of preference, there is a science to what thickness you want to achieve.

  • Too thin = risks of cracking under the weight
  • Too thick = more costs and difficult to pour and level.

In general, for normal use, you want to aim for 100mm thickness.

What’s the Rebate requirements?

The “rebate” of a slab or foundation is the trickiest part of the whole process. It is recommended to have an elevated area on the slab that actually makes the inside floor part of your shed.

The shed walls are just over the edge of this elevated area, so the inside of the shed is higher making it impossible for water to get in through the bottom.

If the concreted area (slab) was flat, water could flow through on the floor of the shed.

Make Sure it’s Square

This may seem redundant but if you don’t get your angels right you can be in trouble when erecting the shed.

Make sure to check the measurements all meet up accurately so it’s a perfect square or rectangle.

The main thing is to check you have the exact dimensions of the shed kit you are buying or bought before measuring and laying concrete. Also to confirm the dimensions from the supplier to ensure it’s not an ‘approximate’ measurement provided on their product listing.

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