A storage shed or garden shed can be an excellent addition to your property, increasing property value, storage space and convenience or even acting as a workspace. However, to protect the shed and its contents, your storage shed needs a solid, stable foundation. You want to make sure your storage shed is installed properly so you can use it for many years.
Some particularly small sheds – those less than 8 x 8 feet weighing less than 300 pounds including the contents – may not need a foundation. Other storage sheds, such as those intended for especially heavy equipment, like tractors, or those that don’t have a built-in floor, may need a concrete slab foundation. However, for most sheds, a crushed stone foundation is sufficient and appropriate. This provides both drainage and stability while being relatively inexpensive and simple to construct.
It is essential to note that this type of foundation is usually referred to as a “gravel” foundation but is in fact made of crushed stone of a specific size and grade. Site Preparations explains that actual gravel is rounded river rock, which will not lock up properly to create a stable surface. Make sure to look for “3/4 clean” crushed stone, which is no larger than 3/4 of an inch in size and has been washed to remove dust and residue. Crushed stone that hasn’t been washed can lock up too tightly and may not allow for proper drainage.
The first step to laying a foundation for your shed is choosing the site. Plan for your foundation to extend a foot in each direction from all the walls of the shed for a total width and length that is 2 feet greater than the shed’s footprint. Understand where the utility lines on your property are located. Call 811, the nationally designated phone number for requesting utility line marking on your property.
Next, consider local ordinances, building codes and homeowner association bylaws. These rules and specifications may dictate how far away from structures, roads and property lines your shed must be located and what percentage of your property it can cover. In addition, these codes will often address frostproofing and anchoring if the frost line or high winds are a concern in your area.
With all of these considerations in mind, choose your shed’s future location. Pick a site that has good drainage and has not been recently disturbed by construction. In addition, a site that’s not too sloped makes laying the foundation much easier, as does a site without much obstruction or debris, such as stumps.
Building the Foundation
The general steps for laying the foundation are clearing and tamping the ground, laying and anchoring the border and pouring and tamping the gravel. You will need at least a 4-inch layer of gravel along every part of your foundation, so dig and measure as necessary.
First, measure the intended area and mark it with marking paint or stakes with string. To ensure this area is square, measure across both diagonals. If the measurements are equal, then the area has the proper square edges. Clear this area of loam (grass) and debris (such as rocks and roots) and tamp the dirt until it is firm and even. Best in Backyards recommends a manual tamping step around the edges even if you use an automatic tamper first. Measure with a level at least 48 inches long to ensure the ground has been properly leveled.
Next, build the perimeter of the foundation. Site Preparations recommends using wood that is at least 4 x 4 inches in dimension and not only pressure-treated but ground-contact rated. As you lay the wood in the cleared area, make sure it is absolutely level and adjust the tamping of the dirt underneath as necessary. Secure the wood at each corner with 1/2-inch rebar pounded at least 2 feet deep or deeper if the frost line dictates it. Use a 1/2-inch auger bit to drill holes at the corners and every 6 to 8 inches in between and then pound in the rebar. Build up the perimeter enough that there are at least 4 inches of depth for the crushed stone all along the inside.
Finalizing the Site
Once the perimeter is laid, put down a layer of landscaping fabric, weed barrier or construction fabric. Make sure you have enough to lay all the way across the ground, going up 2 inches along the inside of the perimeter. Pull the fabric taut along the ground and staple it to the inside of the perimeter to hold it in place.
The area is now ready for the crushed stone. Use the level perimeter to make sure the crushed stone is level as you spread it around before you begin to tamp it. Once the entire area has a level layer of crushed stone at least 4 inches deep, you can tamp it in place as the final step. Start a little inside the perimeter and work your way inward in a spiral rather than going back and forth. This prevents the gravel from shifting over to one side as you tamp. Your foundation is now ready for the shed to be placed.
Things You Will Need
- Tape measure
- Marking paint or stakes with string
- 4 x 4-inch wood (pressure-treated and ground-contact rated)
- 1/2-inch auger bit
- Landscaping fabric, weed barrier or construction fabric
- Staple gun
- Crushed stone