Backyard Decks: Build an Island Deck

Create a comfortable retreat anywhere in your yard

Built with composite decking and hidden fasteners, this maintenance-free backyard deck is designed to go together fast and to fit in anywhere in the yard, without footings or ledger boards.

By the DIY experts of The Family Handyman Magazine

TIME

Weekend

COMPLEXITY

Moderate

COST

Over $500

Floating deck

Most decks are attached to houses, but there’s no reason they have to be. Sometimes the best spot to set up a deck chair and relax is at the other end of the yard, tucked into a shady corner of the garden. And if you don’t attach the deck to the house, you don’t need deep frost footings—which can save hours of backbreaking labor, especially in wooded or rocky areas where footings are difficult to dig.

We designed this deck with simple construction in mind. If you can cut boards and drive screws, you can build it. The only power tools you’ll need are a circular saw and a drill, though a miter saw also helps. We used a premium grade of low-maintenance composite decking with hidden fasteners, which brought the total cost to over $2,000, but using standard treated decking and screws would cut the cost by more than half. You may need to special-order composite decking and hidden fasteners if you use the same types we did, but everything else is stocked at home centers or lumberyards.

A few cautions: If all or part of the deck is higher than 30 in. off the ground, you’ll need a building permit and railings. If you intend to build any kind of structure on top of the deck or attach the deck to the house, you also need a permit. If you dig footings, call 811 first to check for underground utilities. Also, keep the deck at least 4 ft. back from the property line.

Figure A: Island Deck

The dimensions of this deck are 11-ft. 8-in. square, not including the stairs.

A complete Materials List and Cutting List is available in pdf format in Additional Information below.

Figure A: Island Deck Figure A: Island Deck
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Place the footings and beams

Lay out the two beams parallel to each other, 9 ft. apart. Screw on temporary 1x4 stretchers across the ends of the beams, overhanging them each the same distance, then measure diagonally to make sure the beams are square to each other. Mark the location of the gravel pads (see Figure A) by cutting the grass with a shovel, then move the beams out of the way and cut out the sod where the gravel will go.

Establish the highest and lowest points with a string and string level to get a rough idea of how deep to dig and how much gravel to put in to make the blocks level (Figure A). Tamp the dirt with a block to make a firm base, then spread the gravel. Place the blocks and level them against each other and in both directions (Photo 1), adding or scraping out gravel as needed. Use construction adhesive between the 4-in.-thick blocks if you stack them, or use 8-in. blocks. If your site slopes so much that one side will be more than 2 ft. off the ground, support it on a 4x4 post on a frost footing instead—it’ll look better and be safer.

Set the beams across the blocks and square them to each other, using the same 1x4 stretchers to hold them parallel and square (Photo 2). If the beams are not perfectly level, shim them with plastic shims (sold in home centers).

Mark the joist locations on the beams, starting with a joist on the end of each beam. We used 11 joists spaced 12 in. on center to keep the composite decking we used from sagging over time, but wood decking can be spaced 16 in. on center.

Instead of toenailing, which often splits the wood, use metal angles to hold down the joists. This also makes it easy to place the joists. Attach one alongside each joist location (Photo 3).

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Cantilever the joists on all sides

Set the two outer joists and the center joist on the beams against the metal angles. Extend the joists over the beam on one side by 10-1/2 in., but let them run long over the opposite beam. Trim them to exact length when the deck is almost done so you can avoid ripping the last deck board.

Fasten the joists to the angles with deck screws. Screw on both rim joists—you’ll have to take the second rim joist back off when the joists are trimmed and then reattach it, but it’s needed to hold the joists straight and to hold the outside joists up (Photo 4). The decking will hold the outside joists up when the rim joist is removed later.

Set the other joists on the beams and fasten them to the beams and rim joists. Reinforce the outside corners with additional blocking (Photo 5). Finally, mark the center of the joists and run blocking between each pair of joists. Set the blocking 1/2 in. to the side of the center mark, alternating from side to side, so that the blocking doesn’t end up in the gap between the deck boards.

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Add a step

The deck surface should be no more than 8 in. above the ground where you step up on it. If it’s close, just build up the ground or add concrete pavers. Otherwise, add a step.

To cantilever the stairs, extend the stair stringers underneath four deck joists, then join the floor joists and stair stringers with reinforcing angles (as we did) or wood 2x4s, which are less expensive (Photo 6). Use a screw first to hold the angles or 2x4 blocks in place, then finish fastening them with nails, which have greater shear strength.

The 5/4 (nominal) decking we used called for a maximum spacing between stair stringers of 9 in. on center, but you can space stringers 16 in. on center if you use solid wood.

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Hidden fasteners create a clean look

We attached the deck boards with hidden fasteners (see Materials List in Additional Information below). Other types of hidden fasteners are available—or you can use deck screws, which create lots of holes but save time and money.

Start with a full board at one side, aligning it with the edge of the rim joist. Leave the boards long at both ends, then cut them back later all at once so the edges are straight. Use four 1/4-in. spacers between each pair of boards as you fasten them, but check the distance to the rim joist after every four boards and adjust spacing if necessary.

At the next to the last board, remove the rim joist and mark and cut the ends off the joists so the last deck board lines up with the edge of the rim joist. Reinstall the rim joist and attach the last boards.

Nail 1/4-in. spacers ripped from treated wood to the rim joist every 16 in. so water won’t get trapped against the rim joist. Screw on skirt boards with two screws at each spacer (Photo 8). Attach the decking to the steps after the skirt boards are fastened.

Finally, finish the steps (Photo 9).

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Required Tools for this Project

Have the necessary tools for this DIY project lined up before you start—you’ll save time and frustration.

  • Hammer
  • Clamps
  • Miter saw
  • Cordless drill
  • Circular saw
  • Line level
  • Level
  • Drill bit set
  • Framing square
  • Safety glasses
  • Spade
  • Speed square

See Additional Information at the end of the Step-by-Step section.