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How To Make A Foundation For Your Garden Shed

A foundation is essential for any shed. It keeps the shape of the shed and provides good anchoring points. A good elevated base will also keep the interior of the shed dry. 

Pick a site for your shed first. Try to visualize what the building will look like in the position selected. Make sure that access is going to be adequate for the intended usage. Take into account the distance from the site to the closest electricity and water points etc.

There are two options for you: a concrete slab or a timber foundation. Both options have their advantages, so it would be best if you considered what your shed is going to be used for before you make a decision. Do you plan to use the shed for garden tool storage, and fertilizer? Or you are going to store your ride on a mower or ATV? The amount of weight you will put on the floor will determine which foundation option you should go with. Also are you the owner of the property or you are planning to move the shed to somewhere with you in the future.

Generally speaking, these two options will have these features:

  • Concrete slab: It will support the most weight and provide a long-term solution. However, it is more expensive and permanent. 
  • Timber foundation: Easy setup and removable. This is the option we usually suggest customers choose unless you have some heavy items you need to store. 

No matter which option you choose, please always make sure the surface is properly levelled. If not, Your Steelmates garden shed will be difficult to be assembled and will cause problems like the doors won't open and close properly and possibly cause leaking. All foundations should also be built above ground level, in order to avoid rainwater running inside. Here are some tips for both options. 

Option 1. Timber foundation


Steelmates offer a detailed floor plan for all the models we sell, it gives you info on timber specs, quantity, and how to put them together. Feel free to contact us if you have not obtained one yet.

In general, all timber used needs to be treated. The bearers on the bottom need to be H4 treated, and others H3.2 treated, which includes joists, plywood or fence paling boards. If the ground is perfectly levelled, which rarely happens, unfortunately, the bearer can be laid on the ground directly, and built on top. If the ground is not level, do not start digging, it will take forever! Instead, all you need are concrete blocks or bricks. Dig shallow holes about 20mm to 30mm deep and fill them with pebbles, these will prevent foundation subsidence. Put blocks or bricks on the pebbles. Each bearer will need 3 supports. These will raise your building off the base altogether, stopping any damp from rising and encouraging air circulation.


Step1: Set bearers

Set the bearers apart in the distance according to the specific floor plan of your shed


Step2: Lay joists

Lay joists on top of the bearers, all edges should overlap. Even the space between joists, the general rule is the gap needs to be smaller than 600mm


Step3: Square joists

Measure the diagonal distance, make sure they are equal. This ensures the layed out timber is in a perfect rectangle. Then fix joists onto bearers.


Step4: Fix floor

Lay the plywood or palings on top, leaving 25mm gap all around. The rebate is reserved for the base frame of the shed. The floor is higher so rain water won’t run inside.



Option 2. Concrete slab

The foundation for your shed will be a little bigger than the shed itself, so keep this in mind when selecting your site. Refer to your Owner's Manual for your shed model for the exact dimensions for your concrete slab. You can also find those dimensions under the "Footprint" in the Specification table of every shed. 

Make sure there is a rebate of 30mm wide and 20mm deep around the footprint size, so the interior is raised to stop water from running into the shed.


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