How far apart can deck railing balusters be spaced in New Brunswick?

Deck railing balusters in New Brunswick must be spaced so that the gap between them does not allow a 100mm (4-inch) sphere to pass through at any point. This means the clear space — the open gap measured from the inside face of one baluster to the inside face of the adjacent baluster — must be less than 100mm. This requirement comes from the National Building Code of Canada, which New Brunswick adopts as the basis for its provincial building code, and it applies uniformly to all residential guard systems regardless of deck height, railing material, or design style.

The 100mm rule exists specifically to prevent small children from getting their heads trapped between balusters. A child's body can squeeze through a gap that their head cannot easily pass back through, creating an entrapment and strangulation hazard. The 100mm dimension was established based on anthropometric data about the smallest head size of children in the age range most at risk — roughly 9 months to 3 years old. This is not an arbitrary aesthetic guideline; it is a life-safety provision that inspectors in New Brunswick enforce strictly.

In practical terms, if you are using standard 1.5-inch (38mm) square wood balusters — which are the most common type used on residential decks in New Brunswick — the maximum on-centre spacing works out to approximately 138mm, or just under 5.5 inches. That gives you 38mm of baluster width plus a 100mm gap. However, most builders in New Brunswick space balusters at roughly 4-inch (100mm) on-centre intervals, which provides a clear gap of approximately 62mm (about 2.5 inches) between balusters. This tighter spacing exceeds code requirements but provides a more visually balanced appearance and a greater margin of safety.

The 100mm rule applies not just to the spaces between balusters but to every opening in the guard system. This includes the gap between the bottom rail and the deck surface, the gap between the top rail and the uppermost point of the balusters, the space between the last baluster and a post, and any decorative cutouts or openings in panel-style railings. Every single opening, measured in any direction, must be small enough to prevent a 100mm sphere from passing through. Homeowners sometimes overlook the bottom gap — if your bottom rail sits 5 inches above the deck surface, that is a code violation even if the balusters themselves are properly spaced.

Another critical requirement that intersects with baluster spacing is the anti-climbing provision. The guard system must not have climbable elements within the lower 600mm (24 inches). This requirement directly influences design choices. Horizontal baluster patterns — where the infill members run side to side instead of vertically — create a ladder-like configuration that children can climb. While the NB code does not outright ban horizontal balusters, the anti-climbing provision effectively requires that if you use them, the spacing must be tight enough that they cannot serve as footholds. Some municipal building departments in New Brunswick interpret this conservatively and discourage horizontal patterns entirely for residential applications.

Cable railing systems face similar scrutiny. Horizontal cables spaced 3 inches apart technically meet the 100mm sphere test if the cables are close enough together, but the horizontal orientation creates a potential climbing hazard. Some New Brunswick municipalities restrict cable railings on decks at certain heights, or require additional measures to address the climbing risk. If you are considering cable railings, check with your local building department before purchasing materials.

When installing balusters, consistency is important both for appearance and for code compliance. Measure and mark your spacing carefully, using a jig or spacer block cut to slightly under 100mm to ensure every gap is uniform. An inspector will check multiple gaps across the railing run, and even one gap that exceeds 100mm can result in a failed inspection.

---

Find a Deck Building Contractor

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

• R.e.j Construction ✓
• Worry No More Handyman Services ✓
• Eastbound Homes ✓