If you’re going to be building a shed and you don’t want it to start rotting, you need to keep it from coming into contact with the ground.
Ideally, your shed should be at least four inches off the ground. This ensures airflow to keep the ground dryer underneath and discourage mold and mildew. Even treated lumber can succumb to moisture over time.
The distance also discourages termites and other insects. If you’ve ever seen a musty-smelling shed with mildew creeping over items inside or algae growing up the siding, you’ll see why keeping your shed off the ground is a good idea.
Do I Need a Foundation For a Shed?
A foundation is necessary to keep the shed level, to keep it away from insects such as termites, and to keep moisture away from it. Moisture can seep up from the ground and not only deteriorate the lower wooden parts of the shed but also cause dampness inside.
Eventually, you may end up with mold and mildew on some of the items inside. If your shed isn’t level the windows and doors will stick. Even if you level the dirt before you put down your shed, it won’t stay perfectly even over the years and you will eventually end up with a shed that leans.
Even a slight angle can cause boards and panels to pull apart. It’s much better to put the shed on a solid foundation, whether buying a shed or building one. If you want a shed that can be moved, many of the foundation types allow for moving the shed. If your dealing with a sinking shed read my article How to Lift a Sunken Shed Foundation? for information to raise your shed.
The Main 4 Foundation Options
Concrete paving stones can be used as a foundation if your site is level. If your area experiences high winds, you may want to consider using bigger paving stones and anchoring the shed to them. One to two inches of dirt should be dug out of your space to level the ground and filled with gravel before setting the stones.
This method is good for level ground and firm, well-drained soil, as the shed may shift over time. If you have a large shed or soft or soggy soil, another foundation would be better.
Gravel foundation If you have flat ground or a small slope and firm soil, you might consider a framed by 4x4s. If you buy a shed without floor joists you’ll need pressure-treated 2x4s to put under the shed as joists. Make sure the gravel is compacted and level.
Treated wood frame on concrete blocks is another easy foundation type. One unique advantage of this type is that the blocks can be stacked to level your shed on small slopes up to six degrees, as long as it’s not going to be in a windy area. Solid blocks should be used, as the hollow ones may crack over time. This type of foundation is good for smaller sheds on firm soil.
Pier or deck blocks. A better variation of the wood frame construction. This needs to be built on level, firm ground, but if you have problems with standing water, the distance underneath your shed provided by the blocks will handle that problem.
Pier blocks come with brackets that fit various sizes of lumber, which are attached with screws. Deck blocks have channels for the lumber to rest without fastening. While the blocks can be laid on the ground, it’s best to set them in gravel for drainage. You do have to watch for block sinking over time. If you need more options for a shed foundation read my article What’s The Best Shed Foundation Option For You?
Can I Put Shed On Top Of a Concrete Slab?
A shed certainly can be put on a concrete slab. It’s the most permanent and stable foundation type, but also the most expensive. This type of foundation is a permanent foundation and is good for larger sheds or those that will store heavy objects such as lawn tractors.
The slab has to be poured to a depth below the frost line, so those living in colder climates will need some digging. This type is suitable for any size shed or soil type. It can even be used on small slopes. However, considering the excavation requirements and skills needed in framing and pouring the concrete, this type of foundation usually involves hiring somebody to do the work.
Be sure to put some kind of moisture barrier between the concrete and wood frame. Moisture can seep from the ground through the concrete and into your shed, causing lichen and moss growth and even wood rot on the outside and mildew inside.
What is the Best Base to Put a Shed On?
A concrete pier foundation is the most versatile of all types. It’s suitable for all sizes of sheds, all types of soil, and slopes. This involves digging holes that extend below the frost line plus another four to six inches to fill with gravel. Concrete is then poured into the ground, and usually up to six inches above ground.
Ask your concrete supplier about forms for this job. Brackets to fit your shed frame are sunk into the concrete before it dries. Since posts can be attached to the brackets as well as the base frame, this foundation can be used on slopes to level the shed. The airflow underneath keeps the ground dry and prevents moisture problems.
It also keeps insects such as termites away from the shed. The only drawback, if it is one, is that you will need to build steps to the shed or a ramp for your lawnmower. Here’s an article on the best shed foundation base, How to Build Your Shed Floor on Skids.
What is The Cheapest Base For a Shed?
The least expensive foundation for a shed would consist of pressure-treated 4x4s laid parallel. The bottom shed is then attached to that. If your shed is small you can use just two runners. If the ground is not completely level, you can use gravel underneath the skids to level it out.
Concrete blocks placed every four feet or so will keep the wood off the ground. Even though pressure-treated lumber resists rot and insects, it isn’t indestructible. If you have a problem with standing water the blocks will help.
The advantage of this type of foundation is that it’s easy to build as well as being cheap. It also enables the shed to be moved in the future. However, it is best for small sheds that won’t store anything really heavy and those on solid, harder ground.
It’s not as stable on sandy or soft soils. This type will tend to shift over time with unstable ground or if there is a lot of activity or movement in the shed, so another type may suit your situation better.
A shed foundation choice shouldn’t be only a matter of cheapest or easiest to build. In considering a foundation, you must keep in mind a few things: the size of your shed, your soil type, the levelness of your ground, the activity level inside, and the weight of items you plan to store. If you put your shed on a solid foundation, it will serve you well for many years.