Getting a decking order right

Board counts are arithmetic. These are the things that make the arithmetic wrong before you ever pick up a tape.

• Measuring the frame, not the decking. Decking usually overhangs the rim joist by an inch or so on open sides. Measure the surface you intend to cover.
• Buying nominal widths. A "6 inch" board is 5.5 in once milled. Sizing off 6 in leaves you roughly 9% short — on a big deck that is a second trip.
• Skipping the gap. Boards need the 0.125 in gap to drain and to move with humidity. Butting them tight traps water and cups the boards.
• Ordering exact. Ten percent covers bowed boards, knots and cut-offs. It is cheaper than a second delivery.

Joists, beams and footings

Joist and footing counts vary with span tables, beam placement and local frost depth. Treat any number you get from a calculator as a shopping estimate, not a structural design, and check your local code before you build.