How to Construct a Shed Foundation
A long-lasting shed will need a sturdy foundation to keep it level and protect it from moisture. Learn how to construct a shed foundation in this Lowe’s video:
For a detailed tools and materials list and project instructions, click here.
Before you begin, check local building codes or homeowner’s association guidelines regarding permits, frost lines and location specs in your yard. Also, call 811 to check for underground utilities.
Pick a spot for your shed that’s close to level and doesn’t collect water. It’s also good to have three feet of clearance around the perimeter from things like fences and structures. To ensure you have enough space at your location, mark the shed area with mason string and batter boards. To square it, measure three feet along one string and four feet along the adjacent string. The distance between the two points should be five feet. Adjust as needed and check the other corners.
You can build your foundation several ways. On-grade foundations are for areas that don’t freeze. One option is a concrete slab and with sill plates on top. Another option is masonry blocks set on four inches of gravel.
For frost-proof foundations, the footers are set below the frost line to prevent shifting during freezing temperatures. You’ll need additional strings and batter boards to line up post holes and runners. For the shed featured in this video, posts are set on concrete footers:
1. Dig holes about four feet apart, 12 inches in diameter and 12 inches below the frost line. Pour about 4-6 inches of gravel in the hole, compact it and then add concrete following the manufacturer’s directions. Once the concrete has cured, set a post on top of the footer. Making sure the post is plumb and holding it straight, add concrete around the sides and top off with soil. 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 with a saw. Then attach post base brackets and 4×4 runners.
2. Build the frame with 2x4s and nails according to your shed’s directions. Set the frame on the 4x4s, leaving an overhang at the ends, and attach one side to each 4×4 with one screw. Check for square by measuring the diagonals – they 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.
3. Set a floor panel at the corner of the frame, flush to the edges. Nail down the short edge, check the frame for square one more time, and nail down the rest of the plywood. Attach the other floor panels according to the directions.
With the foundation set, you’re ready to build the shed. Kits come with detailed instructions to do it yourself or have it professionally installed.
