What's In This Article
An on-grade foundation is suitable for all solid build sheds up to 160 square feet.
A permanent foundation is suitable for larger sheds. Why do you need a foundation?
Sheds should sit on a solid foundation because moisture causes wood to rot and metal rust.
Foundations raise the shed off the ground so doors open easily, and the shed lasts longer.
A good foundation also keeps the structure stable and less likely to move during inclement weather.
Here is how to build a shed floor base.
Before building anything, check with the Building Inspector first.
They can tell you if you’re allowed to do something and how much work you’ll need to put into it.
You might need permits or licenses and your local Building Inspector will help you get everything you need.
A safe place to build a shed should be level, and not collect too much water. You need enough room to move around to get things done.
Frost lines vary based on climate. You should know what your frost line is and how to protect your house from the cold.
Contact your HOA or use this frost line map to find out more about frost lines in your area.
You should avoid building sheds near trees because roots can easily damage foundations.
If you plan to put up a shed, make sure there is enough space for electrical outlets.
A shed foundation should be located at least two feet away from any permanent fire pit, furniture, swing set, or other structure.
The location of the shed should allow for easy access to utilities such as water and electric lines. There shouldn’t be any overhanging branches or close proximity to trees.
Generally, you will need the following tools to start building a shed floor base:
- Chalk reel
- Concrete leveling blocks
- Tape measure
If you don’t have all the tools and budget is an issue you could consider hiring them for the job, search online for a local tradesman that hires them out for a reasonable fee.
Frost Proof Or On Grade?
Sheds can be built on grade foundations and are super easy to install.
They are strong enough to support heavy loads. However, they aren’t as durable as frost-proof foundations.
On-grade foundation is the most common type of foundation used for sheds. and requires very little maintenance.
Permanent foundation is the more expensive option but offers better stability.
Concrete paver foundations are great for smaller sheds. They are easy to install and inexpensive.
But they’re not ideal for larger sheds because they require digging up the dirt and filling holes with gravel.
For bigger sheds, you’ll want to consider other types of foundations.
A flat surface is perfect for a garden shed. Soil should be firm, well-draining, and free of rocks or other obstacles.
Gravel should be placed directly over soil. This prevents weeds from growing up through the gravel.
What type of foundation you choose will largely depend upon what size you want your shed.
Sheds should be built using materials that are strong enough to hold the weight of the structure and the contents.
A gravel pad, paved block foundation, or concrete slab foundation is recommended for smaller sheds. Larger sheds need more substantial foundations.
Solid concrete blocks and lumber are suitable for larger sheds.
Deck blocks and lumber are also recommended for large sheds. Sheds should be built using a deep foundation because they’re large and heavy.
Concrete piers and lumber foundations are also recommended for large constructions.
Prepare The Area
A shed needs to be built near a flat surface without any obstacles or obstructions. Sheds should be built at least 16 inches away from walls, fences, and other buildings.
Mason lines and batter boards are used to make sure there is adequate space for the shed.
The shed must be built around the post supporting the runners. Measure 3 feet along one string, and 4 feet along the next string.
The distance between them should be 5 feet. Mark the locations of the strings on the batter boards. Use the strings to check the other corners.
An assistant is needed to measure and adjust for squares. Post holes should be about 4 ft apart. Batter boards and mason lines can be set up to mark these points.
You can use string to check for squares at intersections. Adjust string along with the batter board if necessary. And mark the location of the string on the batter board.
Dig post holes 12 inches in diameter and 12 inches below the frost line.
Pour about four to six inches of gravel into the hole, compact it, and then add concrete following the manufacturer’s directions.
If you move the batter board, use marks on the board to return it to its original position.
Consult with local building code officials to determine the frost line depth in the area you’re working in.
Once the concrete has hardened, set posts on top of the footers. Square them using the mason line as a guide.
Add concrete around the sides and brace each post to keep it upright. Hold the posts steady until the concrete hardens.
A shed should be built using treated lumber rated for ground-contact use. Fasteners and hardware used in the assembly must also be labeled for treated lumber.
When installing the shed floor, make sure you measure the height you want for the floor before marking any posts.
Then, use these measurements to mark the posts and cut them with a saw. Wear protective equipment when working with treated lumber.
A shed floor frame uses treated 2-by-2s and nails. The frame is built using four 2-by-4 pieces. Two sides of the frame are attached to each piece.
Square up the frame by measuring the diagonals. Use two screws to attach each corner of the frame to the 2-by-4.
Level And Level Again
Building a shed foundation can be hard work and you need to ensure you don’t make mistakes as they can be time-consuming to put right.
You need to stake out the perimeter of the shed, and then level the string before building the foundation.
A flat stone should be used to level the ground, and then you can use the wood piece to level the dirt and gravel.
Levels should be checked frequently during construction to ensure the foundation sits straight.
Gravel foundations distribute the weight of sheds evenly over the entire frame. This helps prevent rot and decay.
Anyone with at least intermediate construction or tools skills can handle installing a gravel pad.
Plus, there’s no need to get a cement truck in your yard to lay this foundation! You can bring in all your supplies with a wheelbarrow, and use hand tools to complete the job.
Gravel foundations are easy to install, but there are several things you should know before you start building them.
First, if you want to use gravel, you need to make sure that the soil underneath your house is well-drained.
Second, you must check with your local building department to see what kind of footings you need to install.
Wooden Frame/Concrete Blocks
Concrete blocks are inexpensive and offer great versatility when building a shed. Blocks are easy to work with and can be stacked to accommodate any slope.
This type of foundation requires less excavation than other foundations and doesn’t require a subfloor or floor joist system.
It’s a great foundation option for those who want to build a sturdy shed without spending too much money.
This option is very durable and stable, but it does require some work. It is also not ideal for soft soils or slopes.
This type of foundation is also a good option for those who are new to this kind of work and want to take on the challenge themselves.
It is easy to construct and requires very few materials.
Blocks must be leveled before construction. The size of the shed dictates the number of blocks needed and corner support and center support are necessary for stability.
A simple shed made out of concrete blocks varies in price so it is worth shopping around.
You need to consider how much money you want to spend before building your shed and this should be done at the planning stage.
This type of foundation is suitable for flat yards or slopes up to 24″ of difference. Leveling kits are recommended when building this shed.
Unfortunately, this product isn’t recommended if you need more support for slopes greater than 30 inches.
Wooden Frame/Pier, Deck Blocks
Deck blocks are square-based pyramidal in shape. Their channels are at the top for wood framing.
They sit on the ground and need to be leveled, and level with each other. Shed dimensions determine the number of blocks needed.
You need to support each corner and 6′ to 8′ on the perimeter (closer if heavy equipment).
An 8′ x 12′ shed would use six-deck blocks – three per long side. Good choice for flat lots, not sloped.
This kind of foundation requires a lot of work, but it’s worth it because it’s very sturdy.
A shed made out of concrete blocks is great for people who love nature and need a place to store their tools or garden equipment.
A metal bracket holds the lumber in place while the lumber is secured with wood screws.
Deck blocks don’t have any brackets or screws. Both types of blocks are made of concrete, however, pier blocks are cheaper than deck blocks.
To avoid ground sinkage, gravel and landscape fabric should be used around the base of your shed to help prevent this problem.
Concrete slabs are required for a strong and permanent foundation.
If you are planning on building a heavyweight construction the foundation needs to be made of solid material to support the heavyweight.
The concrete slab should be wide enough to cover the whole base of the wall and it should be deep enough to hold up the weight of the structure.
The slab should have holes drilled into it for drainage and these holes should be covered by a waterproof membrane.
The slabs will need to be reinforced with and installed using Simpson wedges. The anchors should be embedded at least 2 inches deep into the concrete.
Concrete slabs need to be at least 4 inches high. Remember to make sure you’re following local laws and regulations when installing concrete slabs so you don’t get any nasty fines or surprises.
Building On Skids
Skid foundations are used to support buildings. They’re fast and easy to build but they’re not suitable for sites that are too steep.
Skids are usually made of treated wood or you can make your own skids by using 2x4s or 2x6s and nailing them together.
Don’t use untreated wood as it won’t last very long and will cost more in the long run.
Skids should be laid on a bed of gravel before they’re used. Gravel creates a very stable base, but you’ll need to check the excavated areas to see if they’re level.
If not, remove some more soil from the high points. Add 3 inches of gravel to the excavated areas.
Then compact the gravel with a hand tamping machine or gas-powered plate compactor, then place the skids back into place.
Here’s a 2-step guide:
Toe nail all joists to skids using 16d nails. Measure diagonals from opposing corners on each side of the skid to make sure it’s perfectly square.
Make sure you nail them dead center. Whatever method you choose to anchor your shed, make sure it’s done before laying down and napping your floor sheeting.
Anchoring your shed floor is crucial for stability.
You should start by laying out the floor sheeting. Start with the short side first.
Then pull the long side over to align with the outside edge of your floor framing. Make sure that everything is aligned correctly before nailing down the floor sheeting.
Put down the first layer of plywood over the entire floor.
Then put down another piece of plywood over top of the first piece. Continue this process until you’ve covered the entire floor.
Plywood is a very strong material used to build floors. It is often used to cover concrete or cement floors as the last part of the foundation building process.
To avoid squeaky floors, you need to lay the plywood flat and use screws instead of nails. A shed platform should be constructed in such a way as to use the least amount of wood possible.
Plywood is commonly used because of its strength and durability. A 2×6 stud wall should be placed perpendicular to the ground, and then built up with plywood to form the floor.
This will help reduce waste and make the structure more sturdy. What type of plywood should be used?
Plywood should be thicker than 1/2″ because if you’re going to store something heavy inside the shed, it needs to be protected.
Pressure-treated plywood is easier to work with, but regular exterior grade plywood is fine too.
Cutting The Lumbar
The next step is to cut the lumber to the size you need and attach the pieces together. You can save time by cutting the lumber before assembly.
It’s best to use exterior screws instead of nails. Remember to factor in the blade’s width when choosing the length of boards.
To work it out, always subtract 1⁄8″ for any cuts to a board then mark the location of each edge brace before drilling holes for attachment with screws.
Sheds aren’t required to be built against a wall. However, certain sheds are designed to take advantage by being attached to the wall.
To make it a freestanding shed you’ll need to build a conventional wall along the back of the shed. Plywood siding should be installed over the entire wall.
You may use any type of siding as long as it meets the requirements
For a freestanding shed, you can build on concrete slabs or pour concrete footings. You’ll also need to install rafters and roof trusses and attach them to the walls.
This type of shed requires more materials than a conventional wood-frame shed.
Some typical lean-to sheds are built using pressure-treated lumber. They are usually made out of tongue and groove plywood and asphalt shingles.
The roof is often made out of T1-11 plywood. The fascia and rake trim is made out of 1×3 wood.
The door trims can be made out of wood and the door hinges are made out of galvanized nails. The latches are made out of outdoor screws.
The roofing materials include 15 pounds felt, metal framing brackets and door hinges and latch. The exterior of the shed can be painted, stained, or preserved.
A simple gravel shed site prep will cost around $5.00 to $9.00 per square foot. The cost includes the labor and materials needed to prepare the ground for a new shed.
Gravel is by far the cheapest and easy to use.
The average price for a shed foundation is $10.00 to $20.00 per square foot depending on the thickness and quality of the concrete.
Location is also important when calculating cost because if you put your shed near a busy road, you’ll be paying more for maintenance.
Quality also matters and you should get a high-quality shed pad if you want to avoid future problems.
DIY foundation building is satisfying and if you take your time and work hard you could have some additional space to enjoy quicker than you might think!