Laying a Concrete Slab For Your Garden Shed

Laying a Concrete Slab For Your Garden Shed


Laying a concrete slab could be the most challenging part of building a garden shed. And what’s more, garden shed kits do not normally come with a floor base.   So really, if you had no base, once put it up you will have the roof and the walls and no floor.

So before buying a shed or at the very least before assembling your garden shed you need to decide on what its foundation will be and of course where it will be built.

You can…

  • Sit your shed on a soft surface like the ground and anchor it down
  • Use pavers or small stones for your base.
  • Purchase or build a steel/timber flower kit
  • lay a concrete slab

Manufacturers and safety standards recommended to lay a concrete slab for your shed’s base. The reason is it will be a better more solid foundation to anchor your shed too, will keep water out from the base, and give you a level surface.

Below are some handy tips on laying down a concrete slab for your garden shed and a full demonstration of the process with a video to make this step easy for you.

TIP #1 Levelling & Clearing the Site

It may seem obvious but sometimes this step can be rushed and leave you at risk of an uneven and cracked foundation. Making sure you take the time to clear the site of any loose rocks and sticks, level the ground with some garden tools, and check it’s even with a leveler or using points.

You can find out more details >> How to Properly Prepare the Ground for a Garden Shed Foundation

TIP #2 To Rebate or Not to Rebate Your Concrete Slab

Although not required, it is strongly recommended to include a rebated edge to your concrete slab. This helps prevents water from getting around the base and into your garden shed.

That ledge will allow the shed to sit below the slab level and prevent water from reaching the upper level of the slab.

If you’re planning a rebated slab make you check with your shed manual and supplier whats the best dimensions are. Below is an example of a general slab rebate formula:

Concrete Slab - drawing

If this looks overwhelming you can always hire a local handyman or concreter to do the job for you.

It certainly is worth it, you will have a solid foundation that will look professional, will be waterproof and secure.


  1. It is important to first select a good, reasonably level site for your slab.
  2. Once you have chosen a site, clear the area, and remove any grass.
  3. Using pegs, roughly mark out the area and determine how much digging will be required. Now, dig out the area.
  4. Visually establish high points and low points and use soil to level the area as best as possible.
  5. Measure and construct the box away from where you plan to put the slab.
  6. This gives you room to maneuver and work.
  7. 30 by 100 millimeter treated pine is ideal for the box frame.
  8. In this case, the box dimensions are 3.1m by 3.1m, which allows for a 50-millimeter rebate.
  9. Once you have dug the area out and made it as level as you can, place the box in the area.
  10. The required thickness of your slab is 100 millimetres.
  11. Using a spirit level, fill or dig out areas in order to ensure the box is level.
  12. In this area, there is a slight slope in the land running into a far corner.
  13. This makes the area around 180 millimeters; too low so we need to bring it up by even and fill remembering that how slab thickness is 100 millimetres.
  14. Now that the boxing is in position, build up a level, drive pins into the corners, and sides to stop the box from moving. Paint pegs or wooden stakes are ideal.
  15. In some cases, you may need more than one peg on the side.
  16. It is important to check the depth of the area you will be filling with concrete.
  17. Place a straight edge tint before crossing the length and brink of the box.
  18. Use a spirit level and check the depth of the area within the box.
  19. Remember, it has to be 100 millimeters because that is the thickness of your slab.
  20. Fill in areas too low and remove those areas too high.
  21. Ensure that the fall of the slab follows the contour of the land.
  22. Now that the area is level, lightly wet it down this will assist with compacting. The next step is to lay the building plastic down and line the area.
  23. Place reinforcing steel mesh on top of the plastic.
  24. A light f52 gauge mesh is required.
  25. This holds the concrete together and helps stop the concrete slab from cracking.
  26. This particular slab will require 1 cubic meter of concrete and we are using a 20 MPA concrete mix, which basically means the stones or gravel use is 20 millimeters.
  27. Pull the concrete in and level it up with shovels to the height of the boxing.
  28. Screen the concrete off with an aluminum screen or length of timber.
  29. Oregon pine is light and inexpensive 70 x 30 millimeters, 4-5 meters long within a person to reach in is ideal.
  30. Simply work the concrete across as demonstrated.
  31. Let the concrete go off or dry out a little for about half an hour, then complete rebate with an edging tool.

And finish off with a trial.

Wait for a day or so depending on your weather conditions and your slab is ready to assemble your Absco Shed.

If you have any comments or questions, please do not hesitate to get in contact with us.

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