All sheds, Garages, or storage buildings must be build on some kind of base, platform or foundation. The foundation must be strong enough to support the building and not allowed to gradually sink if ground is wet or to heave in winter if the frost gets below it.
Note – (There’s a Video farther down on this post)
To plan to build any kind of shed foundation you need to consider;
– The land form: is it level, sloping, sandy, solid clay?
– is it very wet or even flooded at times, or deep frost in winter?
– What is the building used for: light or heavy equipment storage?
– How large is the building? The larger the building, a stronger foundation is needed.
– Consider your budget without sacrificing quality.
The common types of foundations used are;
1. Poured concrete: It’s a solid concrete wall on a footing under the perimeter of the building.
2. A cement block: The blocks are placed on the concrete footing instead of poured concrete.
3 A concrete slab; usually poured on a gravel base and made the size of the shed dimensions.
4. A pressure-treated lumber frame covered with sheets of heavy plywood.
Here are the details.
1. A poured concrete foundation wall is usually used for large buildings, the size of a car garage and larger.
The depth of the wall depends on the frost depth to prevent it from gradually lifting a bit over the years. To prevent
it from sinking, a wide footing of concrete is poured at the bottom of the trench first and after it’s hardened, the foundation wall is build on top. Under the footing, it is best to first pour about 4 – 6 inches of gravel to help with drainage. The height of the wall should be at least six inches or higher above ground level.
2. If a cement-block foundation wall is built, a very strong footing has to be poured first to keep any blocks from sinking. It must be quite a bit wider than the blocks as well as a little deeper to give it more strength.
Choosing between a cement block or solid concrete is a mater of preference and skill. Either one can support a large heavy structure. But for large buildings, the poured concrete might be cheaper.
3. A concrete slab can be poured to form the base of the shed or garage. The floor will be easy to keep clean and it can
also support a car or other heavy equipment. The base should first be dug out and filled with at least about six inches of gravel for good drainage. This method is best if the surface is quite level. If there is a little slope, a partial foundation wall may have to be build. The slab should be at least 4 inches thick and above ground level. It’l sink a bit in time. The structure can then be build on top of the concrete slab.
4. A platform made of treated pressurized lumber might be the cheapest and simplest to build without the mess of concrete,
and is ideal for a garden shed. It can also be raised and adapted to slopes or uneven surfaces as well as sandy or wet areas.
If the ground is fairly solid clay and quite level you can simply lay doun a number of sidewalk slabs and build a framework of
2 x 6’s on top and cover it with 5/8″ or 3/4″ rough waterproof plywood. The garden shed or storage building can then be build on top.
On slopes or sandy and wet areas, you should dig holes under the corners, fill them with a little concrete or at least 6″ of
gravel or both, and install 6″x 6″ posts. Then attach the perimeter joists, level them up, and complete the platform.
Click on this video
Remember, if you build the shed from a kit, and the base is not included, or if you build the shed from scratch, you must first build
a platform or foundation. Many shed building plans include methods to build the base, but many don,t, because there are so many different ways to build it. However, in most large bundles of woodworking plans, (the ones that contain 12,000 to 16,000 different plans with blueprints), an e-book showing how to build a number of different kinds of foundations is included. to get more
information, click here.