How to Build a 12-Foot-by-12-Foot Wood Deck

Determine the location of your deck and lay out its perimeter. Drive a stake into the ground at the location of one corner. Measure 12 feet from the stake to the location of the second corner and drive a stake into the ground at that spot. Determine how high you want your deck to be. Measure that distance from the ground on one corner stake and tie the string to the corner stake at that height. Run the string to the next corner post, using the level to ensure you maintain the correct height. Do not trust a measurement from the ground on the second and subsequent corner posts because the ground might not be level. Use the carpenter's protractor to establish a 90-degree angle from each of the two corner posts. Measure 12 feet from each post and drive a stake in the ground. Continue to run the string completely around the perimeter using the level to maintain the correct height. Tie the string off at each post. Verify your deck layout is square by measuring diagonally between opposing posts. Both diagonal distances should be exactly 12 feet.

Determine the length of your support posts by measuring the distance between the ground and the string on each post. Those lengths will likely be different. Write the measurements down, noting which measurement corresponds to which post. Cut the 4-by-4-inch support posts to length. Replace the stakes with concrete deck footings. Set the support posts into the concrete footings. Toenail the support posts to the footings.

Cut your 2-by-10-inch skirt boards to length. Place one skirt board against the corner posts on one side of the deck, allowing 1 1/2 inches to extend above the top of the posts. Drill two 3/8-inch holes through the skirt boards and corner posts. Insert 3/8-by-6-inch carriage bolts and secure with washers and nuts. Repeat this procedure on the opposite side of the deck.

Cut your 2-by-4-inch ledgers to length. Place the ledgers 1 1/2 inches below the edges of the remaining skirt boards. Attach the ledgers to the skirt boards with 3/8-by-2 1⁄2-inch lag screws. Arrange these skirt boards with their ledgers facing the deck's interior. The ledgers should be even with the top of the corner posts. Drill two 3/8-inch holes through the skirt boards and corner posts, being careful to alternate with the previously installed lag bolts. Attach the skirt boards and ledgers with 3/8-by-6-inch carriage bolts and secure with washers and nuts.

Measure the interior of one opposing pair of skirt boards, marking 24-inch centers. Set your joist hangers in place, with the base of the joist hanger at 9 3/4 inches below the top of the skirt board. This will allow the top of the joints to rest 1 1/2 inches below the top of the skirt board. Attach the joist hangers to the skirt boards with 1 1⁄4-inch joist hanger nails. Measure your 2-by-8 joists and cut them to length. Set the joists in place in the joist hangers.

Arrange your decking boards on top of the joists, but do not secure them. Rearrange the boards until you obtain a pleasing pattern. You might need to cut some of the decking board to make your pattern work. Remember to have a 1/8-inch gap between the boards. Once you are satisfied with the appearance of the deck boards, pre-drill holes in the boards to help prevent splitting. Attach decking boards to the joists, ledgers and skirt boards with 3-inch deck screws.