How to Build a 18 X 12 Deck

Building an outdoor wooden deck will add value to your home.

The Foundation

Decks add value to homes.Decks add value to homes.
To build a secure deck, each step in the process must support and strengthen the construction of the deck. Specific care and concentration must be followed to ensure that the deck you build will be durable enough to last for many years. The project can be handled alone, or with a helper.

Measure a 12- by 18-foot area and stake it off with the string. The 18-foot length of the deck will be against a house or similar structure.

Take the shovel and remove sod from the area, if any. Dig four troughs perpendicular to the house, 12 feet long, 8 inches wide and 4 inches deep. The troughs will be at the edges of the area and 6 feet inside. This will result in three 6-foot sections. Fill each trough with 2 inches of sand and level it off.

Unroll the plastic sheet and cover the entire 12- by 18-foot area. Lower the timbers into the troughs over the plastic, resting against the sand. Level the timbers on the sand. The sand is what will keep them level indefinitely. Spread 2 inches of gravel over the plastic between the timbers. This will prevent any growth of grass or weeds under the deck.

The Support Beams

Lay four rows of support beams along the 12-foot width of deck. These will run along the 18-foot length of the deck and will be 4 feet apart. Each 18-foot row will be made up of three 6-foot lengths of 2- x 6-inch lumber. They will be nailed to the timbers that are 6 feet apart.

Vertical support beams.

Nail the 2- x 6-inch beams vertically on the timbers with the 6-inch width perpendicular to the ground. Nail them with the 2 ½-inch wood nails on a 45 degree angle.

Check to ensure all the support beams are level and solid before beginning the finishing layer.

The Finishing Layer

Use a pencil to position the lumber.

Take a small finishing nail and nail it through a pencil, near the eraser. This will be used to measure the ¼-inch gap between the top layer of 2- by 6-inch strips of lumber.

Top of deck 2- by 6-inch lumber.

Start at one edge of the deck and screw the 12-foot lengths of 2-x 6-inch planks to the support beams. These will now be perpendicular to the house and the support beams. They will lay flat with the 6-inch side parallel to the ground.

Use a circular saw to even out the deck.

Keep using the pencil to space the 2- by 6-inch planks apart. When finished, the deck will have the 12-foot lengths of 2-x 6-inch planks all lined up evenly with their butt ends up against the house. Use the circular saw, if necessary, to trim the edge of the deck so that it is even.

Things You Will Need

  • Circular saw
  • Hammer
  • 2 ½-inch wood nails
  • Tape measure
  • Level
  • Shovel
  • Plastic sheet roll
  • Gravel
  • 2 ¾-inch wood screws
  • Screwdriver
  • Pencil
  • 1 finishing nail
  • Four pressure-treated timbers, 8 inches by 8 inches, each 12 feet long
  • Sand
  • Approximately 12 planks of lumber, 2 inches by 6 inches, each 6 feet long
  • Approximately 65 planks of lumber, 2 inches by 6 inches, each 12 feet long


  • It would be best to use an electric screwdriver.


  • Goggles should always be worn when nailing and sawing wood. Unplug all electrical devices when not in use.

About the Author

Based in Troy, Mich., A.W. Ellison is a cartoonist, artist and writer. His work has appeared in Chicago newspapers and art galleries, as well as his two books, "We're Surrounded by Idiots" and "A Pie in Every Eye." Ellison graduated from Michigan State University with a B.A. in theater.