How to Frame a Shed Floor Over Concrete Piers

There are several ways to build a new shed on your property. Building a platform floor on top of concrete piers is one of the fastest, easiest and least expensive options. It's as easy as clearing an area, digging footings, adding crushed gravel before the piers, and then building the 10-by-12 foot floor platform on top of the concrete piers.

Things You'll Need

• Six concrete pier blocks
• Approximately six full wheelbarrow loads of crushed gravel
• Four pressure-treated 2-by-8 inch boards, 12 feet long
• Ten pressure-treated 2-by-8 inch boards, 10 feet long
• Approximately 5 pounds of 16 penny galvanized nails
• Approximately 5 pounds of 8 penny galvanized nails
• Approximately 5 pounds of 2 inch exterior-grade deck screws
• Six sheets of 3/4 inch thick, 4-by-8 foot, exterior-grade plywood
• Twenty galvanized steel joist hangers

Instructions

Site Layout and Setting Pier s

1. Clear an area that will be just larger than the overall footprint of your new shed. Most areas are not going to be perfectly level but try to level the area.

2. Lay out the locations for the concrete piers so there is one at each corner and one in the middle of each of two opposing sides of the shed. This shed will have six concrete pier blocks to support the floor platform.

3. At each location, dig a hole a few inches larger in diameter than the base of the concrete pier block. Dig the holes at least 4 inches deep, deeper in areas where frost heaving in the winter is an issue.

4. Add a few inches of crushed gravel to each of the six holes and then tamp the gravel tight and level. The gravel will allow for drainage under the piers.

5. Place one pier block at each location. Use a line level to align the tops of all of the piers. You can lift them out of the holes and add additional gravel to make them level. Each block should have a notch in it to accommodate standard framing lumber thickness; be sure the notches are aligned in the same direction on each side of the shed (each side will support one long board).

6. Measure across the top of the pier blocks to ensure that the two rows are 10 feet apart and that all of the blocks are level to each other and evenly spaced before starting to build the floor platform.

Floor Platform Construction

1. Place a 12-foot long 2-by-8 inch board on edge into the notches on top of the concrete pier blocks on each side. These will be the rim joists that the 10-foot floor joists will be attached to. The notches will help keep the boards in place while you work.

2. Measure again to ensure that the two rim Joist boards are exactly 10 feet apart and level to each other. If not, adjust the piers to achieve even and level spacing before continuing.

3. Mark the locations where the 10-foot floor joists will be nailed to the rim joists. The 10-foot joists should be installed on 16-inch centers.

4. Attach the galvanized steel joist hangers to the rim joists using 8 penny galvanized nails, again on the marks for 16-inch centers.

5. Place the 10-foot long boards into the steel joist hangers. Nail the ends of the boards to the joist hangers using 8 penny galvanized nails. Use 16 penny galvanized nails to nail through the rim joist into the ends of the floor joists, at least two or three nails per joist end.

Plywood Floor placement

1. Place one sheet of plywood at a corner of the floor fram. Use the 2 inch deck screws to attach the plywood to the frame making sure that the edges line up to the frame. It may help to snap a chalk line to mark the center line of the top of each joist on the plywood, to ensure you don't miss the joists. Construction adhesive is not required, but if you are seeking a place for solitude and meditation, gluing the plywood to the frame before inserting screws will help keep the floor quiet.

2. Stagger the full sheets of plywood on the frame so that the seams do not create a straight line all the way across the floor. Leave a 1/16 inch gap between each plywood sheets to allow for expansion and to prevent buckling.

3. Trim the plywood sheets to fit the frame as needed. This size platform will require four standard sheets with just a little waste.

4. The floor frame is now ready for installing a roof or walls as desired.

Tips & Warnings

• It is important to make sure that the floor frame is square and level before building the floor.

• Dig down into the soil at each location of the concrete piers to allow at least 4 inches of crushed gravel.

• For extra support, you can double the rim joists by gluing and nailing two 2-by-8 boards together for each joist.

References

• "Sheds and Garages," Scott Atkinson, 2008