How to Build a 12 X 12 Freestanding Deck

Make a 12-foot frame with four 2-by-6-inch treated boards. Stand two boards on edge, parallel to each other and 12 feet apart. Sandwich another board between these two at each end. Ensure the sides are flush with the ends of the first two boards and attach the boards with 2 1/2-inch decking screws.

Mark the corners for the deck at the desired location. Use a tape measure and hammer a stake into the ground at each corner.

Make six parallel rows of precast footings within the corner stakes. Start at one end and position two footings 10 feet apart on center. Place a third footing evenly spaced between the two footings. Set the next row of footings 2 feet 4 inches on center away from the first row.

Position the footings for rows three through five 2 feet 4 3/4 inches apart on center. Set the last row 2 feet 4 inches on center away from row five. Check for correct alignment of the rows before continuing.

Ask an assistant to help lift the 2-by-6-inch frame and set the two slightly longer sides of it in the grooves of the footings -- they would be the frame boards that were positioned inside the first two. Adjust it so there is an equal amount of overhang at the corners. Rest a carpenter's level on top of the boards and check for level. Remove or add soil under the footings if necessary.

Set four 2-by-6-inch support boards, on edge, into the grooves of the footings inside the frame. Attach the boards to the frame from the outside with 2 1/2-inch decking screws.

Position the first 2-by-6-inch surface board on top, perpendicular to the support boards and flush along one side of the deck's frame. Attach the board to the frame and support boards with 2 1/2-inch decking screws. Continue to attach the surface boards as you work your way toward the opposite side of the deck.

Butt the edge of the each surface board against the preceding board if the treated wood is wet. As the wood dries and shrinks, a small space will develop allowing water to drain through the boards. Leave a 1/8-inch gap between surface boards if the wood is dry.