Garden sheds are handy for a whole slew of reasons. You might require some additional storage space for all of your gardening bits and bobs, fancy yourself a DIYer and need an outdoor workshop, or perhaps it’s going to be converted into a home office. Whatever the case, you’re going to need solid foundations. Without them, your outbuilding simply won’t last.
To truly savour the perks of having your dream shed over the years, you’ll need to know how to make a concrete base for a shed of its size and stature. Do it right and you can stave off damp and level the ground, ensuring a warm, neat and tidy haven. Get it wrong or neglect to do it at all and ground water might pose a problem, not to mention an uneven floor.
Before the worry sinks in, though, know that Estate Sawmill’s landscaping pros have got you covered. By reading this tutorial on how to make a shed base, you’ll give your new outbuilding a leg up when it comes to structural integrity. And the best part? It’s fairly easy.
Why does my shed need a base?
(Skip straight to the tutorial if you’re already clued up)
An amateur mistake is assuming that your new shed can be plonked straight on the ground. Whether you’re building it from scratch or choosing between a handful of pre-made models, a base is necessary to safely support its weight, keep the ground level and help with air circulation.
You can take it from us that you can’t achieve this trio of goals by just plonking down a few planks of wood or pavers that you had lying around. There is a special knack to providing the right amount of support. You’ll also need to prepare the ground for your base – i.e., elevate it slightly above ground level – to let the runoff from rainy days drain away properly. On top of that, maintaining a layer between the wet earth and your shed’s floor will protect it from dampness and subsequent rot.
Types of shed bases
There are several types of bases you can build for your shed, and each foundation has its own set of qualities. The four main types are a timber frame, concrete, paving slabs or a plastic base.
Concrete
A concrete foundation can provide the optimum level of stability and moisture protection for your shed. Admittedly, it is one of the most labour-intensive options as building a concrete shed base involves removing any existing turf, levelling the ground and then filling it in with your materials. You’ll also need a sub-base as the concrete can’t be laid directly onto the ground.
Once the work is completed, though, you can smile as it’s absolutely worth it, especially for larger sheds that require additional support due to their weight.
For all of these reasons (and some others), we’re going to focus on how to build a concrete shed base in this tutorial rather than the other options. Keep reading and you’ll understand why.
How to make a concrete base for a shed in 6 steps
With some of the preliminary information covered, there’s nothing left to do except launch into our tutorial. This is how to make a concrete shed base in 6 straightforward steps.
What you’ll need for the job
The right tools and high-grade materials are a must if you want to properly build your foundations and waterproof your shed. If you’re lucky enough to live near a tool-sharing library or other similar neighbourhood scheme, you can hire or borrow the main equipment.
Tools & equipment
- Safety equipment: gloves, dust mask, eyewear, work boots
- Tape measure, pegs, hammer, mallet and string
- Spirit level and set square
- Appropriate groundwork tools: shovel, rake, edger and tamper
- Wheelbarrow, cement mixer and tamping board
- A suitable saw for the timber
Materials
- A suitable hardcore for the sub-base
- Concrete ingredients: mixed ballast, cement, water
- Treated timber to cut to the appropriate size
- A pack of wood screws
An overview
Spoilers! Here are the main steps at a glance:
- 1) Establishing a location in compliance with building regs and your own requirements
- 2) Levelling the site and building the sub-base
- 3) Constructing the formwork to contain the drying concrete
- 4) Mixing the concrete
- 5) Pouring the concrete into the frame
- 6) Installing the shed on top of the completed base
Step 1: Planning and building considerations
Your first step involves sussing out your site. First off, consider whether you’ll need planning permission – it’s likely you won’t as sheds are classed as temporary structures but if you live in a conservation area there might be a few regulations to take note of.
Then think about access and sunlight; after all, you don’t want it blocking out the sunlight to your precious flower beds or preventing easy navigation around the garden. For example, if you’re planning to use the shed as bike storage, can you easily get them inside and out?
Finally, for those intending to make use of the outbuilding as a workshop or garden room, you’ll need to consider the electrics. This should involve consulting a professional electrician.
Step 2: Prepare the site for your sub-base
Concrete bases require a sub-base, so once you’ve run through all of the early considerations, mark out where you want it to go using the pegs/stakes and string, ensuring that when tied they remain straight – this will be directly under where the shed is meant to go.
We recommend creating a sub-base that is the same size or just 25mm smaller than the base of the shed itself. The latter option accounts for moisture as it creates an overhang that prevents water from pooling around the timber runners or shed floor.
As you’ll need to lay 7.5cm of compact hardcore beneath 7.5cm of concrete later on, the sub-base requires around 15cm of depth. Using the ground tools, remove the turf and dig according to the above specifications, checking everything is flat with the spirit level. When you’re happy you can fill in the hole evenly with the hardcore material, compressing it with the tamper before adding a fine layer of ballast, which you can then rake level.
Step 3: Construct your timber frame (formwork)
With the groundwork mostly done, you can move on to building a basic timber frame, otherwise known as formwork. This is to hold the concrete as it dries, providing crucial structural support.
Use 50mm x 50mm timber to make eight wooden pegs, sharpen one of their ends and hammer each into the ground just outside the corners of your shed base. Run string lines between the posts to mark the base edges, checking the corners are exactly 90 degrees using a square.
To position the first plank of your frame, cut your timber to length and position it at one end of the site. Hammer posts at each end, flush with the top of the plank, just outside the formwork area. Don’t forget to level the plank, before securing it to the posts with 50mm wood screws.
Attach the remaining planks in the same way to form a square or rectangle, nailing them together securely at the corners. To reinforce the structure hammer pegs at 1m intervals along the outside of the formwork – this will keep it solid and holding its shape during the concreting.
Step 4: Mix your concrete
It’s time to mix your concrete. You can do this either as a 1:5 ratio of ballast and cement respectively, or simply use a pre-mixed formula. Here, you might need to borrow or hire a mixer.
How much concrete do you need?
Good question! To work out much is required for your concrete shed base, you need to do a quick calculation. It’s as simple as estimating the surface area, so the width of your length multiplied by its length. Then times that number by the depth (7.5cm) to get the volume in cubic metres. You might want to add 5-10% to cover all bases.
Step 5: Pour the fresh concrete into the frame
Before you go about dumping the concrete within the frame, make sure that you wet the sub-base with a light sprinkling of water. It’s best to do this with a small watering can.
Then, beginning in one corner, pour in the concrete. To spread it out evenly grab your shovel and/or rake and use it to distribute the wet mixture evenly, ensuring that you go right up to the edges to avoid any air pockets.
Enlist a helper to support you in compacting the concrete, starting at one end with a tamping board and then steadily pulling it along to create one even, ridged surface. If you notice any excess, you can go in again with the tamping board, dislodging it by sliding it back and forth across the concrete-filled frame. Keep doing this until the entire site is looking nice and even.
Satisfied? Then grab a trowel to go along the edge of the frame to seal the edges of the concrete smoothly and prevent chipping. After this, you can cover it with plastic sheeting and wait for it to set – just make sure it doesn’t touch the drying surface as it will stick.
Step 6: Install the shed on top of the finished concrete base
After 3 days, you should be able to walk on the concrete base, remove the frame and place your shed on top. With all the structural stuff completed, you can then work on the fun things like decking it out with the right equipment and decorating it with the trendiest shed interior ideas.
What about other types of shed bases?
Timber frame (a portabase)
Timber shed bases are a neat way of ensuring your shed remains level, but again they need a sub-base and a good deal of legwork to install. Whilst they don’t involve the extra step of constructing the formwork required to let concrete set effectively, do expect it to take longer than putting down pavers.
Another thing to keep in mind is that to keep your shed untainted by the good ol’ British weather you’ll need to put effort into the treatment and maintenance of the timbers. So if that sounds like too much hassle, concrete is definitely your best bet.
Paving slabs
For those looking for a low-cost, low-effort option laying down paving slabs might be in order. They’re perfectly sufficient for smaller sheds but do take care using them with heavier outbuildings. Like timber shed bases, paving slabs may require some maintenance, particularly as they can shift or sink under the weight of heavier sheds.
Plastic shed bases
Whilst not the most visually appealing option, plastic shed bases work adequately. These lightweight options as super easy to install and they come in kits designed for standard-sized sheds. As they don’t have the best load-bearing capacity, we wouldn’t recommend them for sheds on the larger side.
Shedloads more garden landscaping content
And there we have it: the most efficient way of making a concrete shed base. Using this method any competent DIYer can secure additional structural integrity and weather protection for their outbuildings. All it takes is care, consideration and, of course, a bit of elbow grease.
So, if this has whetted your appetite for more garden landscaping, you’re in for a treat. We have tons of other tutorials over on the rest of our blog. Are you ready to roll up your sleeves?
