How to Make a Foundation for a Floating Deck

Plot six foundation footings for the floating deck, using a tape measure. There should be one footing at each of the four corners and two at the center point of the two longest sides. Mark each location with a wooden stake. Use a shovel to remove the top layer of grass, rocks or soil at each mark so there is a smooth surface for the foundation. Use a compactor to press the soil down and create a firm footing. Pour 1 1/2 inches of gravel into each of the footprints.

Place a single concrete block atop the gravel at the highest of the footing locations and work it back and forth until it settles in firmly. Use a hammer to insert a wooden stake just behind the concrete block. Tie a piece of string to the stake and stretch it diagonally to the farthest opposite corner. Place a block at this corner and hammer the stake into the ground behind it.

Slide the string at the high corner downward until it touches the top of the concrete block. Hang a spirit level from the string at its center point and slide the lower end of the string up or down until it sits perfectly level. Insert as many concrete blocks as necessary to bring the low end up to the level of the string. Spread construction adhesive between the blocks when piling them. Repeat the process with all four corners and the center footings.

Cut 4-by-6 inch wooden beams to the length of the deck you are building, using a circular saw. The beams should sit along the center line of the concrete block footings. Lay two cut beams onto the concrete blocks, one on each side. Use the circular saw to cut two 2-by-4-inch studs to the width of the deck you are building. Place one stud between the two beams at each end. The studs will act as temporary spacers and allow you to properly align the beams.

Stretch the tape measure from one end of a beam to the opposite corner of the opposing beam. Move to the other end of the beam and repeat this measurement. Compare the measurements and adjust until they are equal. The beams will then be properly aligned. Use a level to check that the beams are plumb and adjust as needed using shims. The floating deck foundation is now ready for joists to be installed and for the temporary joists to be removed.