Getting the right base or foundation is crucial to the stability of your garden shed. The base should be level, stable and dry. It should withstand heavy downpours and support the weight of your shed over its life span.
The choice of foundations for your garden shed will largely depend on the type of your shed, its purpose, type of ground it will stand on and a few other factors.
There are four types of foundations or bases suitable for a garden shed:
A concrete slab is most sturdy, but it requires certain skill to create it. Best to hire a professional. If you intend to build it yourself, be sure to read this post – “How to prepare the ground and build concrete foundations for your garden shed“.
Before you pour a concrete slab remember, that it is a permanent structure which cannot be moved. If you decide to move your shed, you will have to build a new foundation and to remove your old one, will require considerate effort..
If you are building a tool shed on a slope or unstable ground, you should consider creating post foundations. To prepare this kind of foundations, 4 x 4 treated wooden posts are sunk into the ground. The rest of the hole is filled with crushed stone then reinforced with concrete poured on top.
All posts must be ideally level or the shed will wobble and collapse. Another option is to use concrete instead of wooden posts, if your ground is very wet and “boggy”.
If your ground is mostly dry and level, you can place your shed on bricks or build a skid foundation made out of wood.
This kind of foundation is not as sturdy and durable as a concrete slab, but it can easily be relocated to another area.
A combination of brick and concrete foundations provides the best base for your garden shed. Concrete foundations ensure that your shed is stable, level, less prone to insect infestation and most important – dry.
Unfortunately, concrete foundations are also the most expensive option, they take much longer to build than a wooden base (concrete takes 7 days to cure) and they require some skill, especially with ground preparation and levelling.
Concrete foundations are ideal for any size and any type of shed, whether it is wooden, metal or plastic, providing the ground in your chosen spot is reasonably firm, drains at least moderatly well and is not prone to flooding.
You must also be reasonably sure of your chosen spot. A concrete slab, once build, cannot be moved to another location. You will have to use reasonable force to break it up and remove it or you will end up with an unsightly concrete patch on your lawn.
I have found an excellent video guide prepared by Lafarge Cement. While Lafarge DIY cement is a very good brand of cement that you can certainly use on this project, but you can use any other brand you have. Just prepare the cement mixture according to the quantities and mixing instructions on the packet and you are good to go.
If concrete is used as a base for the retaining wall, this foundation should be at least twice the width of your bricks (8″/20cm) and a minimum of 4″/10cm thick for a small shed and for larger buildings at least 10″/25cm wide and 6″/15cm thick. If you skimp and go much smaller than these dimensions you are wasting your efforts.
Concrete is also used for shed floor and needs to be at least 3″/8cm thick or it will not be strong enough. On spans over 6’/2m aim for at least 4″/10cm thick on firm ground and if the ground is soft or you intend to raise the floor level due to bad ground drainage, you need to use some aggregate.
Two rows of brick are sufficient for smaller sheds, but for larger sheds or where the surrounding ground slopes, is very soft, or drains slowly after rain, three or more rows would be better.
Building the base brick wall
Constructing and damp proofing the shed floor
Your concrete foundations are now ready and you can start assembling your shed.