The amount of wood you will need for a 12-by-12-foot porch is determined by your deck plans and your experience as a carpenter. Check the return policy of your supplier before purchasing materials. Be sure you can return any unused materials. If you are a novice carpenter, allow for mistakes, overhang, and waste.
The most accurate way to determine the amount of wood you will need for the frame materials is to refer to your detailed plans. You will need a 2-by-10-inch ledger board if you are attaching the deck to the house. Posts are usually constructed from 4-by-4-inch or 6-by-6-inch posts and you will need at least five. You will need 18 boards of 2-by-6-inch lumber or nine 2-by-10 inch boards to build the joists, also known as the beams. You should purchase an additional 25 percent wood to allow for framing pieces and waste.
A 12 -by-12-foot deck will need 144 lineal feet of decking. The amount of individual boards will depend upon the size and type of decking your choose and the amount of space you plan to leave between decking boards. Allow for an additional 15 percent of decking for waste and another additional 15 percent if you plan to lay your decking horizontally.
The amount of wood you need for stairs depends on the height of your deck. Stair stringers are constructed using two 2-by-12- inch pieces of wood and stair treads are constructed using either 2-by-4-inch or 2-by-6-inch boards. You can determine the number of treads you will need by dividing the height of the deck by 7 inches, the typical height of each step.
Adding railings is not only a good safety measure, but also adds a stylish, finished look to your deck. Railing is constructed from nine 4-by-4-inch boards to construct the three sides of railing. Spindles are usually placed 4 inches apart and made from 2-by-2-inch boards. For a 12-by-12-foot deck, you will need 108 of these. You may also choose to add three 1-by-12 inch boards as a skirt board.