Floating decks can be set directly on the ground or, preferably, a bed of gravel. But it's best to support the deck on concrete blocks. This keeps the wood off the ground and away from moisture so the wood stays drier and lasts longer. You can buy special blocks designed for deck support, or you can use standard solid concrete block (the type without holes), which are cheaper and give the deck a lower profile.
What Is a Floating Deck?
Floating decks are standard decks that appear to levitate on top of the ground. In other words, they're free-standing decks that aren't not attached to any structure, including your house. Floating decks are much easier to build than standard attached decks and typically don't require a building permit.
Codes and Regulations
You typically do not need a building permit for a floating ground-level deck, but confirm this with your city's building department before starting your project. In some cases, you may be subject to zoning rules, which govern the size and placement of all structures on a property; your city office will provide guidance.
A deck does not need a handrail or stairs if its walking surface is under 30 inches above the ground. However, it's best to keep a floating deck as low as possible. Even a fall from a height of 12 inches, or so, can easily twist an ankle or cause more serious injury.
If you need to remove more than a few inches of soil to prepare the site for your new deck, call 8-1-1, the national "Call Before You Dig" hotline, to have all underground utility lines marked on your property. This is a free service that may take a few days, so call well in advance of starting your project.
Equipment / Tools
- Tape measure
- Carpenter's level
- Circular saw
- Framing square
- Drill and drill bits
- Landscape fabric and gravel (optional)
- 21 4 x 8 x 16-inch concrete blocks
- 3 1/2-inch and 2 1/2-inch deck screws
- 7 Pressure-treated 2x6s (8 feet long)
- 2 Pressure-treated 2x6s (10 feet long)
- 17 Pressure-treated 5/4 decking boards (10 feet long; typically 1 inch thick by 5 1/2 inches wide)
Prepare the Deck Area
Clear the ground where the deck will be installed, removing grass and all other organic material, as needed. Rake the ground so it is flat and level, and tamp it well with your feet or with a hand tamp tool. If desired, lay down landscape fabric over the soil and add a layer of gravel to prevent weed growth under the deck.
Set the Concrete Blocks
Arrange 21 concrete deck blocks in a rectangle, creating seven rows of three blocks each. Place the four corner blocks so they are 10 feet apart along the long sides of the rectangle and 8 feet apart along the shorts sides, measuring from the centers of the blocks.
Arrange the remaining rows of blocks so all are evenly spaced between the corner blocks. Use a level and a straight 10-foot-long board to make sure all of the blocks are level with one another.
Build the Deck Frame
Clear a flat area of lawn (or use a garage floor or driveway) for building the deck frame. If necessary, you can also build the deck on top of the concrete blocks. Cut seven pressure-treated 2x6 boards to length at 93 inches, using a circular saw or power miter saw; these are the standard joists.
Measure the two 10-foot 2x6s; if they're anything over 10 feet, trim them to exactly 120 inches (lumber often runs a fraction of an inch longer than the nominal dimension; in this case, 10 feet). These long joists are the end joists. Place the two end joists over the ends of two of the standard joists to create a 96-inch-by-120-inch rectangle.
Drill pilot holes, and fasten the pieces together with three 3 1/2-inch deck screws at each corner, using a drill. Measure from the inside of one corner of the frame and make a mark every 19 1/2 inches along one of the 10-foot end joists. Do the same to mark the other end joist.
Place a standard joist so it is centered on each pair of lines, making sure the tops of the joists are flush. Drill pilot holes, and fasten through the end joist and into the standard joist with three 3 1/2-inch screws at each end.
Position the Deck Frame
Place the deck frame onto the concrete blocks so the frame parts rest over the centers of the blocks. Use a framing square to check the corners of the frame for squareness (90-degree angles). Square up the frame, as needed, by pushing diagonally from opposing corners (this takes two people). Re-check with a framing square to ensure the frame is square.
Check the Blocks
Confirm that each concrete block is level and makes solid contact with the deck frame. If necessary, add or remove soil or gravel beneath blocks to adjust their height.
Install the Deck Boards
Measure all of the 10-foot-long deck boards, and trim any as needed so they are 120 inches each. Place one deck board along one long side of the deck frame so it is flush with the outside face of the end joist.
Drill pairs of pilot holes aligned with each standard joist, with one hole going into the end joist and one into the standard joist. Position the holes slightly off-center so they won't interfere with the frame screws. Fasten the deck board to the joists with 2 1/2-inch deck screws.
Install the next 10-foot deck board with two screws in each standard joist, spacing the two deck boards by about 1/8 to 1/4 inch apart. Install the remaining deck boards using the same techniques, spacing them evenly apart.
Tips for Building a Floating Deck
Pressure-treated lumber is the least expensive and most durable option for the deck frame and decking boards. For a modest upgrade, you can opt for Southern yellow pine (SYP) for the decking material, which typically has fewer knots and a better appearance than standard pressure-treated decking. Going further up the scale, there is cedar, followed by redwood. Choose these for looks only; they're not as rot-resistant as treated lumber, despite their reputation for being naturally decay-resistant. Composite decking is also an option. It is generally made from recycled material, requires no finish or maintenance.
You don't have to finish the frame (if you use pressure-treated wood), but any wood decking should be finished with a protective deck stain or similar sealer as soon as the wood is suitably dry. If the decking is left unfinished, it will turn gray and begin to splinter in a matter of months.