How to Build an Exterior Plywood Deck


Most exterior decks have dimensional lumber as their flooring material, instead of plywood. Plywood does not usually have the kind of moisture resistance needed to function as a finished surface. For homeowners intent on building a plywood deck, however, marine plywood -- which has a much greater resistance to moisture than regular plywood -- makes a serviceable decking material. It comes in 4-by-8 panels, holds paint and stains well. Although more expensive, its increased durability makes up for the extra expense. Building a floating deck with a foundation of precast concrete makes construction much easier.

Things You'll Need

  • Pencil
  • Nail
  • String
  • Wood stake
  • Tape measure
  • Concrete block
  • Carpenter's level
  • Boards, 2-by-6
  • String level
  • Drill
  • Deck screws
  • Gravel
  • Marine plywood
  • Circular saw


  • Measure out the deck width against the side of the house with a tape measure. Tack a nail to each mark and wrap a string around it.

  • Measure the length of the deck straight out from the nail, and place a wooden stake. Repeat for the other side.

  • Connect the strings on the nails to the stakes. Pull the string taut and wrap it around each stake.

  • Run another string line between the two wooden stakes.

  • Measure the two diagonals inside the string rectangle. Ensure that the measurements match.


  • Set a concrete block on the ground 13 1/2 inches inside one of marks on the house. Repeat for the other mark. Place a 2-by-6 support board on the divot of each block. Ensure the board aligns with the marks on the house. Check the joist for level.

  • Place a concrete block at each wooden stake. Set a 2-by-6 support between the blocks. Check for level. Run a string line between the support boards next to the house and the ones you just installed. Check for level with a string level.

  • Have a helper position a 2-by-6 end joist against the ends of two support boards. Fasten the joists by drilling 2 1/2-inch deck screws through the joists and into each support board. Repeat for the other side.

  • Join the interior joists to the end boards. Space them 16 inches apart. Screw them in place with deck screws.

  • Set the interior concrete blocks under the joists. Space them in rows about 2 feet apart. Ensure the joists fit comfortably in the divot. Remove soil or add gravel to achieve this, if necessary.

  • Check for level. Remove soil or add gravel to obtain level.


  • Apply a plywood panel to the corner of the framing. Place it flush against the support board and the end joist. Fasten in place by drilling deck screws about 6 inches apart through the plywood and into the joists and support board.

  • Place the next panel in position. Fasten it to the deck with screws at every joist and the support board.

  • Continue fastening the deck panels as you did the first two. Cut end panels to length with a circular saw.

Tips & Warnings

  • Paint or stain your finished deck for a more attractive look.

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