How to Make a Sub Base for a Garden Shed

Written by mason howard | 13/05/2017
How to Make a Sub Base for a Garden Shed
A garden shed can add an attractive accent to your home's landscape. (colonial garden shed image by Kristina Cilia from

Garden sheds are a necessity for any home that has a lawn or garden, as they keep tools accessible, dry and protected. Garden sheds can be placed directly on top of a crushed rock sub base. The crushed rock sub base will provide drainage underneath the shed, keeping the floor of the shed protected from moisture damage.

Outline the square area where the shed will be placed with corner stakes and string. Make the dimensions of the square 2 feet longer on each side than the actual dimensions of the shed.

Use a shovel to dig out 3 inches of ground.

Use a rake to level the bed of the excavated site.

Use a hand tamper to compact the soil in the bed of the excavated site.

Make a retention frame to fit around the inside perimeter of the excavated site out of 4-by-4-inch pressure-treated boards. Saw the boards to match the dimensions of the excavated site and fit them in place. Because the board width is 1 inch more than the depth of the excavated site, the sub base will end up being slightly higher than the surrounding ground. This will elevate the bed and floor of the shed and help keep water from the surrounding area from running in.

Place a 2-by-4-inch board with a level on top on the frame to make sure it is even. Remove or add a little soil underneath a section of the frame if necessary to make it even.

Secure the boards in place by drilling 1/2-inch holes at the corners and centres and hammering 3-feet-long rebar stakes through and into the ground.

Line the bed with weed-blocking fabric. Weed-blocking fabric comes on rolls and is cut with scissors or a utility knife. Cut the fabric so the edges go up the sides of the frame boards. Use a staple gun to staple the edges of the fabric to the frame boards.

Fill the site with crushed rock. Level the crushed rock with a rake. Compact the crushed rock with the tamper.

Backfill around the frame boards with some of the previously dug-up soil. The shed floor support timbers and shed can now be placed on top of the gravel sub base.

Things you need

  • 4 wooden stakes
  • String
  • Shovel
  • Rake
  • Hand tamper
  • 4 pressure-treated boards, 4 inches by 4 inches
  • Saw
  • Drill
  • Hammer
  • 8 rebar stakes, 3 feet long
  • Level
  • 2-by-4-inch board
  • Weed-blocking fabric
  • Scissors or utility knife
  • Staple gun
  • Crushed rock

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