How to Build a Detached Deck

Backyard decks offer the promise of outdoor parties, fun, and food, or just serious one-on-one time with nature. An outdoor deck is the flat, stable, dry surface that sets the stage for barbecue grills, chairs, and outdoor rugs. But if the prospect of building a full-scale attached deck feels daunting, consider an easier alternative: building a detached deck. Whether you situate it by a water feature, within the garden, or near the house, a detached deck helps create a world all its own.

Because detached decks usually remain lower than 30 inches, many communities do not require building permits or require railings and balusters. Be sure to check with your local building department for permit and code requirements. Many homeowners still opt to install rails for increased safety, though. Another benefit of a detached deck is that you do not need to disturb your house’s siding. Attached decks require that you cut away part of the siding to secure a ledger board. Standing independently of other structures, detached decks do not require ledger boards. This deck uses concrete pier blocks as a type of pre-cast foundation to avoid setting wet concrete.

Tools and Supplies You Will Need 

• (9) Concrete pier blocks with metal brackets
• (3) Pressure-treated four-by-fours, each 12 feet long
•  (9) Bags of 0.8 cubic foot 7/8-inch drainage rock
• Two-by-eight pressure treated boards for decking, each 8 feet long
• #9 by 1 1/2-inch external hex flange hex-head connector screws
• #8 x 2 1/2-inch coarse thread polymer coated exterior screws or hidden deck fastener system
• Marking paint
• Tape measure
• Wood stakes
• Twine
• Post hole digger
• Spade
• Wrench set
• Bubble level
• Electric miter saw
• Oil-based wood preservative for cut ends
• Drill, with driver and drill bits
• Carpenter’s pencil
• Circular saw
• Hammer

Instructions 

Mark Out the Deck Area

Choose an open, level area of firm undisturbed soil measuring at least 10 feet by 12 feet. Lay out the nine spots where the concrete pier blocks will rest. Use the tape measure to measure out the spots and use the twine and stakes to create the straight lines. Create marks on the ground with the marking paint.

1. Mark three spots in a straight line, each spot 4 feet on-center from its neighbor.
2. Create a similar line of three spots parallel to the first line and 3 feet away.
3. Create a third line similar to the others, also parallel and 3 feet away.

Determine Depth of Holes

Determine the depths of the holes for the concrete pier blocks. In some areas, you may be able to rest the blocks directly on firm soil after the turf has been removed. Building codes in areas that freeze may require that the pier blocks rest on gravel and in a hole of depth sufficient to extend below the frost line. Always be sure to check with your building department for guidance.

Keep in mind that concrete pier blocks with attached metal brackets tend to be about 11 inches tall. If you need a few inches of extra height, another type of concrete pier block has a hole on top that accepts 4-inch galvanized adjustable pier support brackets.

Dig Holes for the Pier Blocks

If there is any turf, remove the turf. With the post hole digger and spade, dig a hole at each marked spot to the required depth. Create holes that are about 1 1/2 times the width of the pier block base. Generally, pier blocks are 11 1/2 inches at the base, so your holes would be about 18 inches in diameter. Fill with drainage rock to the required height.

Place the Pier Blocks

Set the pier blocks in the designated spaces. For pier blocks with attached brackets, be sure to line up the blocks so that the brackets’ open cradles all run in a straight line. With adjustable bracket piers, the brackets can be rotated 360 degrees.

Dry-Fit the Deck Beams

Rest the three four-by-fours in each of the three sets of pier blocks’ brackets. Push down firmly to make sure that they are properly seated in place.

Check for Level and Adjust

With the bubble level or laser level, check the deck beams for level. Do this from two adjacent sides. If any section is too high or too low, it must be adjusted.

For piers with attached brackets, you must remove the four-by-four, remove the pier block, then either remove or add landscape gravel to bring the pier to the proper height. For piers with adjustable brackets, keep everything in place. Turn the bolt on the bracket clockwise or counter-clockwise to raise or lower the bracket.

Attach the Deck Beams

Fasten the four-by-fours to the brackets. First, drill a pilot hole through the hole in the bracket. Then, with the ratchet wrenches, screw in the flange hex-head connector screws.

Cut the Deck Boards

Deck boards have a wide range of joist spans. Composite and synthetic PVC deck materials have short joist spans: as little as 10 to 16 inches. Because the beams on this project are spaced farther apart, you must use either pressure-treated two-by-sixes or two-by-eights. If in doubt, check with a structural engineer, licensed contractor, or your local building department for guidance.

Because the outer deck beams are 7 feet apart from each other, you can use factory-cut 8 foot-long two-by-sixes or two-by-eights. These will provide for a 6-inch overhang on the two long sides. Besides saving you from cutting boards, the other advantage is that the ends are pressure-treated. If you do decide to cut the ends of the boards, you must treat the cut ends with oil-based wood preservative.

Attach the Deck Boards

Attach the deck boards to the deck beams either with deck screws or with a hidden fastener system.

For deck screws, use two screws per beam, for a total six screws for every deck floorboard. Drive the deck screws directly through the face of the floorboard until the head is level with the top of the board. Be sure to pull away any splinters that develop from screwing into the face of the board.

Hidden fastener systems like Camo and Kreg require a jig that fits over the edge of the board. A special fastener is inserted into the jig and a cordless drill drives the fastener through the side of the board. The position of the fastener and its angle ensure that the fastener will not be visible.