Deck Material & Code Takeoff
Decking boards and footage, joist count at your spacing, fastener boxes, and railing with balusters spaced to the 4 in sphere rule, from the deck footprint.
Joist spacing sets span and decking deflection, not the look: composite decking wants 12 in or tighter, and stairs want 10 in. Baluster spacing is the 4 in sphere rule, measured at the widest point.
How the math works
- Decking: board coverage = (board width + 1/8 in gap) ÷ 12 sq ft per linear foot, with 10% cut waste. A 5.5 in board at a 1/8 in gap covers 0.469 sq ft per foot of board.
- Joists: count = span ÷ spacing + 1. Span tables cap the joist depth: 2x6 at 12 in tops out near 6 ft, 2x8 at 12 in near 9 ft, 2x10 at 16 in near 12 ft. Rim board and ledger add the perimeter.
- Fasteners: 2 per board end per joist plus 1 per intermediate crossing = about 3.2 screws per sq ft; use coated or stainless deck screws, 2½ in at the face.
- Railing: 42 in minimum height on a residential deck, balusters spaced so a 4 in sphere cannot pass (2.4 to 2.5 in on center with 2x2 balusters), 36 in on the stair side, and a 44 in graspable handrail on stairs with 4 in max tread nosing.
- Stairs: one stringer per 30 in of width, 7 to 7¾ in max riser, 10 in min tread, and the top tread must respect the headroom clearance. Treads run 3 ft for a 3 ft wide flight.
How many decking boards for a 16x12 deck?
192 sq ft, 211 sq ft with 10% waste. A 5.5 in board at a 1/8 in gap covers 5.625 sq ft per 12 ft board, so 38 boards of 6x6x12; 10 in nominal wide board covers 9.6 sq ft per board, so 22 boards.
How many joists for a 12 ft span?
At 12 in on center a 12 ft span needs 13 joists, and a 12 ft span needs 2x10s (2x8 at 12 in caps out near 9 ft 7 in). Check the span table for your species and decking, not spacing alone.
How far apart do deck balusters go?
Close enough that a 4 in sphere will not pass through: 2.4 in on center with 2x2 pine balusters, 3.1 in with 1.5 in square composite balusters. Measure at the widest gap, which is at the rail line.