The design of the deck dictates the amount of material you need. For instance, a deck with a large railing requires more material than a deck without a railing, while a deck with a staircase needs extra building material to assemble the stairs. The design depends partly on local building codes. Building codes determine the size requirements of support posts – usually at least 4 by 4 inches – and the required number of posts per length of the unit.
Primary Construction Material
Primary construction material on residential decks is almost always wood. The amount of lumber you need to build a 10-by-30 deck depends upon the design of the joists used to build the deck, the size of the posts, the type of surfacing used and accoutrements such as railings or stairs. A deck with a tightly slatted surface requires more material, for instance, than a deck with large spaces between the surface slats, while a deck with five rows of joists per section requires more lumber than a deck with four rows of joists per section.
Lumber decks require a number of fasteners, or materials used to connect pieces of wood together. Joists, for instance, must attach to the primary support beams in the deck with joist hangers, brackets or some similar mounting device. Local building codes list approved devices for mounting deck joists in any given area. Brackets are also needed to attach posts to the underside of the deck, and support beams to the wall of the house, if necessary. Bolts or screws attach the deck planking to primary support beams.
Determining Material Needs
Determine how much material you need for a deck by creating detailed drawings. Create drawings of each view of the deck, and include in each drawing the piece of material required for each part of the deck and the dimensions of all materials. You typically need to create detailed plans for decks to obtain a building permit, so those plans can be used to determine the detailed materials list.
By way of example, assume you make the top surface of your 10-by-30 deck with 2-by-12 boards. A 2-by-12 board measures 11¼ inches wide. To cover 10 feet of lateral space, you need nine such boards, spaced at about 2 1/3 inches from one another: 120 (10 feet times 12 inches) minus 11¼ multiplied by nine (the width of the boards), divided by eight (the number of spaces between the boards). Therefore, you need nine 2-by-12 boards measuring 30 feet long to cover the entire deck surface, or 18 2-by-12 boards measuring 15 feet, or 54 2-by-12 boards measuring 5 feet. In addition, you need materials for joists, posts and support beams.