How high does a deck railing need to be in California, and what are the stair rules?

Guards: when you need one and how tall

The code calls a deck railing a guard, and the trigger is height. Where the walking surface is more than 30 inches above the floor or grade below, measured within 36 inches horizontally of the edge, a guard is required. Below that height you are free to use a bench, planters or nothing at all as the edge, which is one reason low decks feel so open. On a sloping yard, measure at the worst point; one corner over 30 inches makes the whole edge a guard situation.

For a house in California the guard must be at least 42 inches tall, measured from the deck surface. That is a California amendment in Section R312.1.2 of the state residential code; the national model code it is based on says 36 inches, which is why online answers disagree. On the open side of a stair the guard may drop to 34 inches measured from the tread nosings, and where the top of that guard also serves as the handrail it sits between 34 and 38 inches. Openings in the guard, between balusters, cables or panels, must be small enough that a 4-inch sphere cannot pass through. The guard also has to resist a specified horizontal load at the top, which is why posts are bolted, not nailed, and why a wobbly rail is a code problem and not just an annoyance.

Stair geometry

The residential code sets a maximum riser height of 7 3/4 inches and a minimum tread depth of 10 inches, and it limits how much risers and treads may vary within a flight, because an uneven step is what trips people. Stairs must be at least 36 inches wide. Open risers are permitted on a deck stair as long as the opening does not pass a 4-inch sphere where the stair is more than 30 inches above grade. Every stair needs a landing at the bottom, and the landing has to be a real surface, not dirt.

On the porch stairs we rebuilt in North County, the brief was a stair that looked like it belonged on a century-old cottage. The treads and risers were set to a comfortable, consistent rise and run that meets today's code, and the painted railing was scaled to the old porch while keeping its balusters at current spacing. Code and character are not in conflict if the design starts with both.

Handrails, which are not the same as guards

A handrail is the thing your hand holds on a stair; a guard is the barrier that keeps you from falling off an edge. On a deck stair they are often combined in one assembly, but they have separate rules. A handrail is required on at least one side of a stair with four or more risers, mounted 34 to 38 inches above the line of the tread nosings, continuous for the full flight, and shaped so a hand can actually grip it. A flat 2x6 cap is a fine guard top but is not a graspable handrail; the code describes the profiles that qualify. Handrail ends must return to a wall or post or terminate in a newel so they do not catch sleeves.

Guards on a deck below 30 inches

If your deck is low enough that no guard is required, you may still want one for a toddler, a dog or peace of mind. Any guard you build is free to follow the code's dimensions even when it is optional, and we recommend it; a decorative rail with 6-inch gaps is a trap for a small child whether or not the city requires otherwise. Benches and planters at the edge are our favorite way to define a low deck without a rail.

Materials and the coast

Wood guards are warm and easy to match to a house but are maintenance; the top rail takes the most sun and the baluster bottoms take the most water. Cable and metal systems keep the view but need stainless hardware near the ocean, and cables must be tensioned to meet the 4-inch sphere rule under load. Composite rail systems match composite decks and are low-maintenance but can look heavy. Whatever the material, the posts carry everything, and how they attach to the frame is where we spend the engineering.

• Guard required above 30 inches; minimum 42 inches tall at a house under the California amendment, 34 inches on the open side of a stair.
• No opening that passes a 4-inch sphere.
• Risers 7 3/4 inches maximum, treads 10 inches minimum, stairs 36 inches wide minimum.
• Handrail on four or more risers, 34 to 38 inches above nosings, graspable, with returned ends.
• These are the California Residential Code values as we read them, including the state amendments; the city's plan check is the final word.

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