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If you are building a deck more than 30 inches above the ground, you are going to need a guardrail.

International Residential Code (IRC) for one- and two-family homes (which is followed by most​ city building departments) requires that you install a 36-inch-tall “guard” to prevent anyone from falling from the deck to the grade below. While a half-wall or even a planter box can be used as a guard, most builders and homeowners prefer to use a railing system -- in this case, a cable railing system.

When building a code-compliant cable rail there are two other safety-related concepts you’ll need to take into account:

The cable infill you use to complete your railing system-- whether installed vertically or horizontally--will need to be spaced according IRC code section R312.3: “Required guards shall not have openings from the walking surface to the required guard height which allow passage of a sphere 4 inches in diameter.”

When you’re working with wood or metal pickets, this rule is much more straightforward and easy to comply with. But, because cable is flexible, you’ll need to make additional considerations for “deflection.” If you were to install cable infill with 4-inch spacing, one could easily push a 4-inch sphere between adjacent cables by pulling up on one and down on the other. The simple solution is to compensate by using 3-inch spacing for your cables. You could never put enough tension on the cable to eliminate deflection, and you certainly wouldn’t want to have an intermediate post every foot for support, so reducing the spacing will be your best bet. In fact, most cable rail suppliers offer posts pre-drilled with 3-inch spacing for code compliance.

In 2000, the IRC included the following language in their guardrail requirements: “[guardrails]shall not be constructed with horizontal members or other ornamental pattern that results in a ladder effect.”

Despite the fact that this was stricken from IRC building guidelines in the following year (and the fact that there have been many code updates since), some inspectors are still making judgements based on the idea that “climbable guards” are not safe. If you have small children that love to climb and may not always be under direct supervision, this type of railing may not be the most practical choice. But, regulating organizations including the IRC and the International Code Council (ICC) are firm in their ruling that climbable guards haven’t proven to be a significant hazard, and that prohibiting horizontal features in a guardrail is too restrictive.

With that said, however; it’s important to be aware of the standpoint of the building inspectors in your area before you begin installation of your cable railing system.

If you want a cable railing system, you should have one! This simple, sophisticated update is sure to improve your views and the value of your home. Happy building!