A long-lasting shed will need a sturdy foundation to keep it level and protect it from moisture. Follow these steps to build your shed foundation.

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Check local provincial guidelines for requirements and information about:

  • Required Permits
  • Foundation type
  • Frost line
  • Location
  • Shed size and type


Most municipal governments include guides on the requirements you’ll need before installing your new shed.

Follow the manufacturer's instructions and safety precautions for your shed.

Note: Contact provincial utility location services before beginning so you don’t impact any utility lines that might be beneath your lawn.


Pick the Perfect Spot for Your Shed

Pick a spot for your shed that's close to level and doesn't collect water. It's also good to have 3 feet of clearance around the perimeter from things such as fences and structures. Larger sheds — 160 square feet and up — need 4 feet of clearance. This area gives you room to build the shed.


Mark Out Where Your Shed Will Go

To ensure you have enough space at your location, mark the area with mason's string and batter boards.

For some installations — such as the one described here with runners — the shed overhangs the runners several inches. The runners are set back from the shed frame the distance of the overhang. Set batter boards and mason's string to mark the perimeter of the posts that support the runners.


Square the Area

To square the area, measure 3 feet along one string, and 4 feet along the adjacent string. The distance between the two points should be 5 feet. Adjust the string as needed along the batter boards and mark the location of the string on the batter boards. Check the other corners.

Tip: Enlist a helper when measuring and adjusting for square

Building the Shed Foundation

You can build your foundation several ways. On-grade foundations are for areas that don't freeze, and come with two options:

  • A concrete slab with sill plates on top.
  • Masonry blocks set on 4 inches of gravel.


The next methods are for frost-proof foundations. The footers are set below the frost line to prevent shifting during freezing temperatures. You'll need additional string and batter boards to line up post holes and runners.

The first method uses concrete tube forms on gravel with post base brackets on top.

For our shed, we're using posts set in concrete footers.

Tip: Talk with a local building inspector or look up your local government’s guidelines on the foundation requirements for your area and shed.


Dig Post Holes

The post holes should be about 4 feet. apart. Set up batter boards and mason's string to mark these points. The intersections of the string indicate the locations of a post corner. Use the 3-4-5 method described above to check for square at each intersection. Adjust the string along the batter boards as necessary and mark the location of the string on the batter boards.


Fill the Holes with Gravel & Concrete Mix

Dig the post holes 12 in. in diameter and 12 in. below the frost line. Pour about 4 in. to 6 in. of gravel in the hole, compact it and then add concrete following the manufacturer's mixing directions. If you move the mason's string, use the marks on the batter boards to return it to the correct location.

Tip: Consult with local building code officials for the frost line depth in your area.


Calculate the Shed Floor Height

After all the posts are set, determine the height you want for your shed floor and mark one post. Use this as a guide to mark the other posts and cut the posts with a saw


Attach Brackets & Runners

Attach post base brackets and treated 4x4 runners.


Build the Floor Frame

Build the floor frame with treated 2x4s and nails according to your shed's directions.

Tip: Some shed floor frames use 2x6s.


Set the Frame in Place

Set the frame on the 4x4s, leaving an overhang at the ends, and attach one side to each 4x4 with one screw.


Secure the Frame

Check for square by measuring the diagonals of the frame. Measure between two opposite corners and then measure between the remaining corners. The measurements should be the same. Make any adjustments and secure the other side of the frame to the 4x4s. Then use screws to secure the frame at each point that contacts the 4x4s.


Attach the Panels to the Frame

Next, set a floor panel at the corner of the frame, flush to the edges. Nail down the short edge, and check the frame for square one more time. Make any final adjustments. Nail down the rest of the plywood. Attach the other floor panels according to the directions and check for level.


Build the Shed

With the foundation set, you're ready to build the shed. Kits come with detailed instructions to do it yourself, or you can have it professionally installed.

How To Terms

Tools, products, materials, techniques, building codes, and local regulations change; therefore, Lowe's assumes no liability for omissions, errors, or the outcome of any project. The reader must always exercise reasonable caution, follow current codes and regulations that may apply, and is urged to consult with a licensed professional if in doubt about any procedures.

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