How to Build a Detached Backyard Platform


Building a detached backyard platform, sometimes called an island deck, provides a firm, slightly elevated surface in your yard if you do not have space for a deck next to your home. Placing the platform on concrete blocks protects it from moisture in the ground while keeping the platform detached from any structure, so you maintain the ability to move the platform as needed. This is a project that you and a friend can complete in a weekend.

Things You'll Need

  • Tape measure
  • Spray paint
  • Shovel
  • Tamp
  • Gravel
  • Wooden stakes
  • Hammer
  • 8-inch concrete blocks
  • Level
  • Rubber mallet
  • String
  • Line level
  • 2-by-6 boards
  • Circular saw
  • Safety goggles
  • Galvanized nails
  • 1-by-4 board
  • Angle brackets
  • Drill
  • Galvanized screws
  • Galvanized joist hangers
  • Decking boards

Setting the Footers

  • Mark the location for the platform on the ground by spray-painting the outline of the deck and the location of the concrete support blocks. Place the blocks no more than three feet apart from each other, ringing the perimeter of the platform.

  • Dig holes for the concrete blocks at the locations you marked that are 6 inches deep. Smooth the soil in the bottom of the holes, and tamp it down.

  • Pour 2 inches of gravel into each hole, and tamp it.

  • Drive wooden stakes into the ground 12 inches behind one of the corner holes. Place the stakes so that one is on the back edge of the corner and one is on the side edge. These stakes will be used to check the blocks for level.

  • Place an 8-inch concrete block into the first hole. Lay a level across the block, and tap it down with a rubber mallet to level it if needed.

  • Place 8-inch concrete blocks into each of the other holes.

  • Tie string to one of the wooden stakes you hammered into the ground behind the first stone, and tie the other end to another stake. Check the blocks on the opposite side for level by extending the string and driving the second stake into the ground 12 inches behind the block you are checking.

  • Slide the string up and down on the stakes so that it lies directly on top of the first stone you placed and the stone you are positioning. Place a line level on the string, and adjust the second block as needed until it is level with the first block.

  • Check the other blocks for level, using the same process. When checking the blocks on the same side as the first block, use the wooden stake hammered into the ground on the side of the first block.

Building the Platform

  • Measure and cut 2-by-6 boards to fit the outer edges of the platform, using two boards for each side. Nail the boards together with galvanized nails so that the outer beams on each side consist of two 2-by-6 boards nailed together. Wear safety goggles when sawing the wood.

  • Nail the outer beams of the platform together to form a rectangle.

  • Lay the outer frame on top of the concrete blocks. Check the frame for square by measuring diagonally across it in both directions. If the measurements are different, the frame isn't square. If this is the case, cut a temporary spacer to the proper length from a 1-by-4 board, and place it inside the frame. Check the frame for square again.

  • Attach angle brackets to the inner edges of the corners with galvanized screws to help strengthen the corner joints.

  • Nail galvanized joist hangers to the two inner edges of the frame where the joists will be installed. The joists are the beams that support the decking of the platform and are installed perpendicular to the direction of the platform. Keep the joist hangers spaced no more than 12 inches apart.

  • Measure and cut 2-by-6 boards to be used as the joists. Slide the joists into the joist hangers, and nail them to the joist hangers with galvanized nails.

  • Cut decking boards to fit along the top of the platform, and attach them to the framing with galvanized screws.

  • Construct a second, smaller platform to be a step for the main platform, if desired. Nail the step to the side of the main platform.

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