How to build a concrete base for a wooden shed


It was only a matter of days ago that I wrote an article explaining how much you should expect to pay when building a concrete shed base, but it suddenly dawned on me that I haven’t actually written a full guide explaining how to build a concrete shed base yourself, saving you money compared to paying a professional to do the work for you.

To be honest, it really isn’t all that hard with most hands on people being able to do the work. In fact it’s one of the easier jobs I do as a landscape gardener and one I look forward to doing too. Before starting my full guide on how to build your very own concrete shed base, let’s take a look at the tools you will need.

What tools will I need to build a shed base?

  • Hand saw for cutting the timber frame
  • Spirit level for levelling the timber frame and possibly the cement
  • Hammer for anchoring the steaks for the frame into the ground
  • Screws for securing the steaks to the edging boards
  • Drill
  • Shovel
  • Cement mixer
  • Wheel barrow

Step 1 – Dig the area to where you will be building your shed base

There are essentially 2 ways to build your concrete shed base. One would be to dig the ground out and have the shed base at the same level as the surrounding ground, or to raise the concrete shed base meaning that it will sit above ground. Let’s start with the assumption that you want the shed base at ground level.

The first thing you will need to do is mark the area that needs to be dug. If for example you have a 6×8 foot shed going on top of the concrete base, then I would recommend marking the area as 6.5 x 8.5 foot at an absolute minimum. This allows for any overhang should the shed be that little bit larger than expected.

If you are going up against a wall like the one pictured below, then I would recommend even more of an overhang, as much as a foot, especially if you have an apex roof. If the roof overhangs the shed walls, then the base of the shed will need to be pushed away from the wall, and therefore needing a slightly larger concrete shed base. The one pictured below was built for a 6×6 feet shed but we built a 7×7 feet shed base.

Once you’ve marked the area, dig to a depth of 6 inches. This will allow for 2 inches of type 1 MOT (similar to hardcore) and 4 inches of sand & cement. I can only go by what I recommend, but I have seen shed bases built to a depth of 3 inches with no hardcore and have had no problems, but anything like this will come with its risks over a long period of time.

If you are going to be elevating the concrete shed base from the ground then you may get away with minimal digging but I will get into this more below.

Step 2 – Build a timber frame around the area that you will be building a shed base

Building a level frame around where the concrete base will be is vital to making sure that your shed base is going to be level. We always purchase 6 inch gravel boards when building our frames as 6 inches is the level that we want to go to so it helps make sure that the depth is correct, as well as being cheap enough to keep costs down. Oh and don’t forget to purchase some batton to cut into stakes for screwing and anchoring your edging boards into the ground, 2×1 will do the job just fine. Below is a picture of where you should be when the frame has been built for your concrete shed base.

If you are going to be elevating the concrete base above ground then you will still need to dig a shallow trench to create a level ground for the frame to be built. If there are any gaps between the timber and the surrounding earth then back fill and tamper down to make sure that no concrete can escape from the frame when being poured.

Step 3 – Lay your type 1 MOT

Again, not everyone bothers using type 1 MOT when building a shed base and most have had no problems (just being honest), but as a professional landscape gardener it is recommended doing so and we always use it.

But be careful! It may sound silly but if your having your concrete base above ground then avoid laying the type 1 MOT or hardcore against the timber frame. This is because once the concrete has set and you remove the edging boards, you will see a level of type 1 at the bottom of the base, and it won’t look great to say the least. As well as this you have the risk of the type 1 moving and weakening the shed base. If however, your having the shed base at ground level, then no one will see the type 1 MOT so fill the hole area.

A rule of thumb when purchasing materials in bulk bags is that the type 1 MOT will cover approximately 8 squared meters (86 squared feet) at a depth of 2 inches. A 6×8 feet concrete shed base will need 48 squared feet of type 1 MOT so 1 bulk bag will be more than enough. Of course you can purchase smaller bags but this will be less cost effective.

Once the type 1 MOT has been put down, be sure to use a wacker plate to create a compact sub base.

Step 4 – It’s time to lay your sand and cement to finish your concrete shed base

When I say sand and cement, more specifically I mean ballast and cement since ballast contains stones, creating a harder concrete base. A bulk bag of ballast will have the same coverage as any other material which is 8 squared meters at a depth of 2 inches (50mm). Given that we have dug to a depth of 6 inches (150mm) and layed 2 inches of type 1 (50mm) we have a depth of 4 inches (100mm) of concrete to pour. This means that our coverage of 8 squared meters at a depth of 2 inches is halved to 4 squared meters, meaning that 2 bulk bags of ballast will be needed to be safe. I would recommend purchasing 4 bags of cement per bulk bag of ballast, so 8 bags of cement in total.

You will need to mix your sand and cement at a ratio of 5 to 1. This means that for every 5 shovels of ballast, you will need to add 1 shovel of cement to the mix. Be sure to keep it wet, but not too wet. The best way to explain would be that it needs to be just wet enough that when you run a trowel across it that it creates a smooth surface, without making puddles.

When you start pouring the cement into the timber frame, start on a corner and keep building your way up to the top of the timber frame and make your way across to the other corner. If you have a spirit level or other straight object that can reach from one side to the other then all you need to do is place this onto each side of the frame and drag the cement towards you, whilst making up and down motions. I hope this is making sense…

The up and down motions will create a smooth surface as you pull the cement towards you, whilst the outer frame is keeping the base level. If puddles have formed, then simply place some more cement onto these puddles and repeat with the spirit level until they have been smoothed over. It’s really easy!

If you don’t have a timber frame all the way around where your concrete shed base will be, for example if you are up against a wall, then you wont be able to make full use of the level frame. I would recommend putting a long spirit level of the side that you do have a frame and holding the spirit level from the other side to tamper the cement down, keeping an eye on the bubble as you do this!

Be sure to also tamper the edges down to make sure that the cement is compact against the frame. This will ensure a nice smooth finish when removing the edging boards from your concrete shed base.

Once the area is filled, that’s it! Walk away and leave it for a few days to set! Here is what the finished concrete shed base should look like.

In short, here are the steps to building your very own concrete shed base

  1. Dig the area to a depth of 6 inches
  2. Build a level timber frame
  3. Lay type 1 MOT to a depth of 2 inches
  4. Mix ballast and cement to a ratio of 5 to 1 and fill the area

And that’s it! In most cases you can complete a 6×8 sized shed in a day with 2 of you. If you would like to know how much you should expect to pay to build a shed base then you can see my full price guide here.

If I’ve missed anything or you have any questions then why not comment below? Or you can even visit our forum here where all of us are waiting with the answers to each others questions.

2 Comments Add yours

Leave a Reply