How far apart can balusters be on a railing?
Openings can't allow a 4-inch sphere to pass through (IRC R312.1.3).
Required guards must be built so that no opening between the walking surface and the required guard height allows a 4-inch (102 mm) sphere to pass. For typical vertical balusters, that means clear spacing of less than 4 inches.
Two exceptions apply on stairs: the triangular opening formed by the riser, tread, and bottom rail may pass up to a 6-inch sphere, and openings in a guard on the open side of a stair may pass up to a 4⅜-inch sphere.
Related answers
- At what height does a deck, porch, or stair need a guard? — IRC §R312.1.1
- How tall do guardrails and deck railings need to be? — IRC §R312.1.2
- How much force does a deck guardrail or handrail have to resist? — IRC §R301.5
- How high does a window sill have to be above the floor to meet fall-protection rules? — IRC §R312.2.1
- How high should a stair handrail be and what size is actually graspable? — IRC §R311.7.8
- How do I attach a deck ledger to the house? — IRC §R507.2
- What is the deck lateral load connection requirement? — IRC §R507.2.3
- How much bearing do floor joists and girders need at the ends? — IRC §R502.6
Need this scoped to your jurisdiction?
Adopted edition and local amendments vary by city and county. Ask Donnie checks your jurisdiction and cites the exact adopted section.
Ask Donnie →General information based on the International Residential Code (a model code). This is AI assistance to verify — not legal advice. Confirm the adopted edition and any local amendments with your local building department (AHJ) and a licensed professional before you build.