What is the proper joist spacing for a residential deck in Dieppe NB?

The proper joist spacing for a residential deck in Dieppe NB is 16 inches on centre for wood decking and 12 inches on centre for composite or PVC decking. These measurements are taken from the centre of one joist to the centre of the next, and they apply uniformly across the deck surface to ensure consistent support and prevent sagging or bouncing between joists over time.

The 16-inch on-centre standard for wood decking, whether you are using pressure-treated lumber, cedar, or another species, is derived from the span tables in the National Building Code of Canada. At this spacing, standard 5/4x6 deck boards (which are actually about 1 inch thick and 5.5 inches wide) have adequate support to resist deflection under foot traffic and furniture loads without feeling springy. For 2x6 deck boards, which are thicker at 1.5 inches, 16-inch spacing provides even more rigidity, and some builders will go to 24-inch spacing with 2x6 boards on simple, low-traffic structures. However, 24-inch spacing is uncommon for quality deck work because it creates a noticeable flex underfoot and makes the deck feel less solid.

Composite and PVC decking requires the tighter 12-inch on-centre joist spacing because these manufactured boards have different structural properties than solid wood. Composite boards are more flexible across their span than a wood board of similar dimensions, and they will develop visible sag between joists over time if the span is too wide. Every major composite manufacturer, including Trex, TimberTech, Fiberon, and AZEK, specifies maximum joist spacing in their installation guides, and 16 inches is typically the absolute maximum for straight-run installations. For diagonal board patterns, which are popular for visual interest, the maximum joist spacing drops to 12 inches for most composite products, and some manufacturers require it even tighter at 10 inches for 45-degree diagonal installations. Since many homeowners in Dieppe choose composite decking for its low maintenance in the Maritime climate, planning for 12-inch spacing from the start gives you the flexibility to install boards in any direction without reworking the framing.

For Dieppe specifically, there is a practical climate consideration that influences joist spacing decisions. The Greater Moncton area including Dieppe receives significant snow loads, and decks must support this accumulated weight in addition to normal live loads. Tighter joist spacing creates a stronger overall deck platform, which handles snow loads with a greater safety margin. A deck framed at 12 inches on centre is roughly 33 percent stronger in surface load distribution than the same deck at 16 inches on centre, simply because there are more support members sharing the load.

The joist material itself matters alongside the spacing. In Dieppe, pressure-treated SPF (spruce-pine-fir) is the standard joist material, with 2x8 being the minimum size for most residential decks and 2x10 being common for longer spans. For joist spans up to about 10 feet, 2x8 joists at 16 inches on centre are adequate for wood decking. Push the span to 12 or 14 feet and you need 2x10 joists to stay within deflection limits. When using 12-inch spacing for composite decking, the added number of joists means more lumber, more hangers, and more fasteners, which increases material cost by roughly 20 to 30 percent compared to 16-inch spacing. This is a standard cost of building with composite and should be factored into the project budget from the beginning rather than treated as an upgrade.

Blocking between joists is also important for decks in Dieppe's climate. Solid blocking at 4-to-6-foot intervals prevents joists from twisting or rolling over time, which is especially important with the wet-dry and freeze-thaw cycling the framing endures annually.

---

Find a Deck Building Contractor

New Brunswick Decks connects you with experienced contractors through the https://newbrunswickconstructionnetwork.com:

• Duguay Construction ✓
• Eastbound Homes ✓
• Larmondin Carpentry ✓