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Storage sheds are most stable with a concrete foundation, but concrete is not the only kind of base a shed can sit on. Other kinds of shed foundations include gravel and wood.
Does a Shed Have to Sit on Concrete? Sheds can sit on a concrete foundation, stone foundation, wooden foundation, or on gravel. Depending on local building ordinances, you may be required to have a certain kind of shed foundation. Check with your local building inspector if you are unsure if the foundation of your shed is up to code.
Keep reading to find out more about the different kinds of shed foundations and how they work. Here are the pros and cons of the different kinds of storage shed foundation materials.
Concrete Foundation vs. Other Kinds of Shed Foundations
Some small sheds will not need any kind of foundation. They can be set on top of stone and anchored to the earth using augers. Larger sheds will probably need a foundation system with heavy duty anchoring to keep up with building codes.
The best place to start your research about shed foundations is to check local ordinances and consult with building inspectors. This may be the most straightforward way to find out what kind of foundation is required by law. Once you figure out what kind of foundation local building codes require, you can narrow down your choices to see what foundation is best for your shed.
You may be tempted to just put your shed on the ground as it is, without a foundation. This is not advisable for a number of reasons and will shorten the lifespan of your shed.
Things to Consider About Foundations for Sheds:
- Price of materials
- Difficulty of installation
- Size of the shed
- Weight of the shed
- If the ground is level or not
- Local weather conditions
- Local building laws and codes
- Tools required
Concrete Foundations for Sheds
The best type of foundational support for a storage shed or garden shed is going to be a concrete slab. While the concrete is still wet you can anchor the shed to the base for the strongest connection.
The size of the concrete slab should be the same as the shed and no bigger or smaller. When the concrete slab is much larger than the shed it allows for water to puddle on top of the concrete and that can cause rot and water damage inside of the shed.
|Concrete Slab Pros||Concrete Slab Cons|
|● Will not be affected by insects or animals (like termites)|
● Does not warp or move
● Creates a sturdy base for anchoring
● Anchors can be installed in wet concrete
● Very clean
● Concrete slab can be the floor of the shed
|● Difficult installation usually requires professional help unless you are experienced in pouring concrete yourself|
● Is very expensive in both materials and labor
● Permanent location
● Water can pool on top of the concrete slab
Areas which have frequent storms and high winds should only use concrete foundations with heavy duty anchors placed around the perimeter of the concrete slab to hold the shed down. The concrete slab should come up out of the ground by about four inches. This also helps with adding external anchoring later. Another thing to consider is the frost line.
What is a Frost Line?
A frost line is the depth of the soil where groundwater begins to freeze. Another word for this is freezing depth. When the temperature drops below freezing the water in the soil will freeze and cause the soil to expand.
How Do Frost Lines Shift Foundations?
When the water in the soil freezes over, it causes the soil to expand. The expansion of the soil can cause the foundation of the shed to shift or crack.
How to Avoid the Frost Line?
The frost line varies depending on the region. The best way to get an accurate answer about where the frost line sits in your area is to consult with a local building inspector.
Wooden Foundations For Sheds
Wood alone is usually not enough to hold up a shed. That is why wooden frames for foundations sometimes incorporate the use of concrete blocks. The concrete blocks are placed around the perimeter of the base of the wood foundation to add more stability. You can also use treated wood if you do not want to use concrete blocks.
Wooden foundations do not sit directly on the ground. The wooden foundation is attached to poles or pillars of wood which go down deep into the ground to create an anchor. It is essential to be careful with the depth of the installation of the wood pillars to ensure that the foundation sits completely even.
|Wooden Foundation Pros||Wooden Foundation Cons|
● Saves significant costs
● Wood insulates
● Can be custom built in any size
● Anchors into the ground with wooden beams or augers
● Easier to move than concrete
● Easier labor
|● Could be damaged by wood-burrowing insects like termites|
● If wood is untreated it can rot with water damage
● Wood can bend or warp with moisture and temperature
Why Does Wood for Foundations Need to Be Treated?
Untreated wood will be susceptible to moisture. Moisture can cause beams of wood to swell or shrink, becoming warped and destabilizing the foundation. In order for a wood foundation to effectively withstand the effects of moisture it needs to be pressure treated.
Gravel Foundations For Sheds
A good option for small to medium sized sheds is a gravel foundation. These are relatively easy to install and offer a good amount of support. Gravel can withstand more heavy sheds than a wooden foundation can.
Gravel is usually not strong enough for large and heavy sheds. Concrete is the best to use for large sheds, but gravel can work for smaller ones. Installing a gravel foundation is easier than a concrete one. All you have to do is dig a hole the exact size of the shed, fill it with gravel, and level the gravel. With a gravel foundation you will need to anchor the shed itself to the ground using augers.
|Gravel Foundation Pros||Gravel Foundation Cons|
|● Gravel drains water and moisture|
● Easy installation process
● Work best with pre-made sheds
● Less expensive than concrete
● Easy to remove if you want to move the shed
|● Does not support heavy sheds enough|
● Is not as strong as concrete
● Does not provide a floor for the shed
What is an auger?
Augers are a kind of anchoring system used for sheds. They are basically large corkscrews which screw deep into the soil to hold down the shed.
Concrete Blocks Foundations For Sheds
We talked a little bit about using concrete blocks in combination with a wood foundation, but you can also use just rows of concrete blocks. This method does not give you any way to anchor down the shed using the foundation so you will need to use augers or dig holes filled with concrete to add brackets to in the corners of the shed.
If you are planning on moving your shed at any point in the future then concrete blocks may be a good solution for you since they are easy to move. It is only recommended to use concrete blocks for small to medium sized sheds. The most important thing about using concrete blocks as a foundation is ensuring that they are leveled.
|Concrete Block Pros||Concrete Block Cons|
● Easy to move
● Easy to install
● Materials are inexpensive
|● Only works with small sheds|
● Can not withstand heavy pressure
● May shift easily
● Can be difficult to level out
● Not enough support
Can you use concrete blocks for large sheds?
Using concrete blocks for a foundation is only going to work properly for small to medium sized sheds. A large, heavy storage shed full of machinery needs more support than concrete blocks could offer.
What is the Best Foundation For Sheds
The best foundation for large sheds, garages, or sheds that contain heavy machinery is a solid slab of concrete. You can install anchors directly into the concrete slab. Concrete slabs are great for sheds that do not come with a premade floor because you can use the concrete as the floor. Having space in between the shed floor and the concrete slab could create a place where water can pool so it is best to have the shed sitting directly on the concrete.
Some people think that gravel is the best solution for shed foundations overall. This is mainly because gravel or crushed stone is great at draining water. It can prevent water damage this way. Gravel may not provide enough support for some sheds however. For anchoring, you can use a combination of a gravel base and concrete pillars in the four corners of the shed.
Some small sheds will not require a foundation. They will just need to be anchored down to the ground with augers, straps, or cords to keep it from flying away. Small, lightweight sheds are fine to build on top of wooden or concrete block foundations. Keep the location of the shed more versatile by using an impermanent foundation like gravel or blocks instead of a solid slab of concrete.
Gravel, wood, and concrete are the three most common types of shed foundations. Small sheds can make do with concrete blocks or gravel, but for large sheds you really want to have a solid concrete slab as the base. While you are building the foundation you should be thinking about how to incorporate an anchoring system. The shed’s base must be leveled, water resistant, and anchored to the shed.