What's the right joist spacing for a Vancouver PT deck?

For pressure-treated lumber decks in Metro Vancouver, joist spacing depends on your decking material and joist size, but 16 inches on center is the most common spacing for standard 2x8 or 2x10 joists with 5/4-inch PT decking boards.

The BC Building Code requires deck joists to support a minimum live load of 1.9 kPa (40 psf), and proper joist spacing ensures your deck meets this structural requirement while preventing bounce and deflection. For 5/4-inch (32mm) pressure-treated decking — the standard thickness — you can space 2x8 joists up to 16 inches on center for spans up to 9 feet, and 2x10 joists up to 16 inches on center for spans up to 12 feet.

Metro Vancouver's wet climate makes proper joist spacing even more critical because moisture-weakened lumber loses structural capacity over time. PT lumber in Vancouver's 60-80% humidity environment stays at higher moisture content year-round compared to drier climates, which can increase deflection and bounce if joists are spaced too far apart. Many experienced Vancouver deck builders actually prefer 12-inch joist spacing for a more solid feel underfoot, especially for larger decks or areas that will support heavy furniture, planters, or hot tubs.

For composite decking over PT framing, most manufacturers require 12-inch joist spacing maximum because composite boards are less rigid than wood. Trex, TimberTech, and Fiberon all specify 12 inches on center in their installation guides. This tighter spacing prevents the flexing and bounce that can cause composite boards to crack or pull away from fasteners over time.

Joist sizing and spacing work together — if you're using 2x6 joists (not recommended for most deck applications), you'd need to reduce spacing to 12 inches maximum and limit spans to 6-8 feet. For longer spans common in Vancouver's larger deck projects, 2x10 or 2x12 joists at 16-inch spacing provide better structural performance and reduce the need for intermediate beams.

Always use joist hangers approved for outdoor use — galvanized or stainless steel hangers with the proper nails or screws. Vancouver's moisture accelerates corrosion of standard hardware, and joist hanger failure is a serious structural concern. The connection between joists and the ledger board (attached to your house) is especially critical and must be engineered to resist both gravity loads and seismic forces per BC Building Code requirements.

When to hire a professional: While joist spacing might seem straightforward, calculating proper beam sizes, post spacing, and footing requirements for your specific deck dimensions and loads requires structural knowledge. Any deck over 600mm (2 feet) above grade requires a building permit in Metro Vancouver, and the permit application must show proper structural design including joist spacing, beam sizing, and connection details.