How To Build a Detached Deck
A backyard deck offers the promise of outdoor parties, fun, food, and time with nature. But if the prospect of building a full-scale attached deck feels daunting, consider an easier alternative: a detached deck. A detached deck is a low deck that is not attached to the side of the house. This type of deck, as opposed to an attached deck, creates a cozy setting wherever it's placed, whether it's by a water feature or within a garden.
Because detached decks usually remain lower than 30 inches, many communities do not require building permits or railings and balusters. Many homeowners still opt to install rails for increased safety. Be sure to check with your local building department for permit and code requirements.
Another benefit of a detached deck is that it does not disturb the siding of your home. Attached decks require that you cut away part of the siding to secure a ledger board, but detached decks stand alone and do not require ledger boards. Instead, this deck uses concrete pier blocks as a type of pre-cast foundation to avoid setting wet concrete and large, deep footings. Though a detached deck offers ease of installation and lower costs, at the same time, it may bring a lower resale value than full-scale attached decks.
What You'll Need
Equipment / Tools
- Marking paint
- Tape measure
- Wood stakes
- Post-hole digger
- Wrench set
- Bubble level
- Electric miter saw
- Drill, with driver and drill bits
- Carpenter's pencil
- Circular saw
- 9 Concrete pier blocks with metal brackets
- 3 12-foot long Pressure-treated 4-by-4 boards
- 9 0.8 cubic feet Bags of 7/8-inch drainage rocks
- 8-foot long Pressure-treated 2-by-8 boards or 2-by-6 boards for decking
- #9 by 1 1/2-inch External hex flange hex-head connector screws
- #8 by 2 1/2-inch Coarse thread polymer-coated exterior screws or hidden deck fastener system
- Oil-based wood preservative for cut ends
Mark Out the Deck Area
- Choose an open, level area of firm undisturbed soil measuring at least 10 feet by 12 feet for this 8-foot by 12-foot deck.
- Using a tape measure, lay out the nine spots where the concrete pier blocks will rest.
- Mark three spots in a straight line, each spot 4 feet on-center from its neighbor.
- Create a similar line of three spots parallel to the first line and 3 feet away.
- Create a third line similar to the others, also parallel and 3 feet away.
Determine the Depth of Holes
Determine the depths of the holes for the concrete pier blocks. 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 a 4-inch galvanized adjustable pier support bracket.
Dig Holes for the Pier Blocks
- Remove any 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 rotate 360 degrees.
Dry-Fit the Deck Beams
- Rest the three 4-by-4 boards in each of the three sets of pier blocks' brackets.
- Push down firmly to make sure that they are properly seated in place.
Check Leveling and Adjust
- With the bubble level or laser level, check if the deck beams are 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 4-by-4 board, 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 4-by-4 boards to the brackets by drilling 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 inches to 16 inches. Because the beams on this project are spaced farther apart, you must use pressure-treated boards. 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 2-by-6 boards or 2-by-8 boards. These will provide 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.
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 of 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.