Building code requirements for exterior decking railings and stairways are especially stringent because properly built decks can help prevent serious injury. In a four-year study, the Consumer Product Safety Commission found that close to 179,000 people were injured on decks and porches, with over 11 percent of those injuries being the result of structural failure or collapse. It's important to keep on top of the building code requirements for decks because the code is continually changing.
For example, your older deck may have toe-nailed connections—wood connections made with nails simply driven through the joints at an angle. If so, be advised that toe-nailing is no longer an accepted connection, according to the current International Building Code (IBC). Older decks using older construction methods may be grandfathered in, but new requirements are mandated whenever you build a new deck or remodel or repair an older deck.
Deck Code Terminology
As a model code, the IBC is developed by the International Code Council for states, cities, and other local groups to both adopt and adapt for their use. As a result, your locality may adapt the IBC to suit the needs of its citizens. Be sure to speak to your local permitting office and consult your applicable code before building.
Understanding the code requirements is easier if you fully understand the terminology that is used:
- Guardrails: A guardrail (sometimes simply called a guard) runs horizontally along a landing or other flat area with a drop on the other side. As the terms are defined by the code, a guardrail is different than a railing—which is a similar feature found on a stairway
- Railing: As the terms are used by the code, a railing is a form of guard that protects stairs, running on the incline up and down the stairway.
- Balusters: Balusters are small vertical in-fill posts running between the guardrail or railing, designed to prevent people, particularly children, from falling off the deck through the space below an angled stairway railing or the horizontal guardrail.
- Grade: Grade refers to the ground level directly adjoining the deck.
- Low-rise decks: Also called ground-level or floating decks, low-rise decks do not rise more than 30 inches above the ground and thus are exempt from certain guardrail and baluster requirements. Another benefit is that low-rise decks often do not require a building permit.
- Rise: Rise is the vertical distance from one stair tread to another.
- Tread: Tread is the flat part of a staircase that you place your foot on.
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Deck Guardrail Height
Deck guardrails (guards) should rise to at least 36 inches above the residential deck level. This is a minimum required height for residential structure—higher guards are acceptable. Commercial deck guardrails, such as those found at restaurants, bars, and at multifamily homes such as apartments or condos, are required to be 42 inches high, minimum.
When Is a Deck Guardrail Not Needed?
Some decks are not required to have guardrails, provided those decks are no more than 30 inches above grade. If you see a deck that has no guardrails (also called a low-rise deck), this might be the reason: its height is below 30 inches.
Guardrails on Low-Rise Decks
Even with very short, low-rise decks, many homeowners still opt to construct guardrails.
If you do decide to include a guardrail on a low deck, its height and the spacing of the balusters is up to you. However, these guardrails still must be as strong as those on higher decks. It is understood that people will lean against guards, and code requires that these guardrails be strong enough to resist collapsing.
Adding hand railing to a low-rise deck is often a very good idea. Disabled people, too, can benefit from having guardrails on low-rise decks.
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Requirements for Deck Stairs
The code has some very specific requirements for deck stairs:
- Stair rails on decks should be between 34 inches and 38 inches high, measured vertically from the nose of the tread to the top of the rail.
- Treads must be at least 10 inches deep, measuring from front to back.
- Stair treads must sustain a weight of at least 300 pounds in an area no more than four inches square.
- The rise, or the vertical distance from one tread to the next, can be no more than 7 1/4 inches high.
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Deck Balusters and Benches
Deck balusters: Balusters are required to be 4 inches apart or less. One classic rule of thumb: a 4-inch diameter ball should barely be able to fit between the balusters. The reasoning is that this 4-inch space is the average diameter of a baby's head, to prevent their heads from getting stuck.
Where balusters butt up against a lower railing, the gap between the bottom of the railing and the deck surface also must be no more than 4 inches.
Deck benches: Homeowners concerned about preserving the view from their decks may wonder if benches are acceptable substitutes for deck guardrails. Unfortunately, benches are not an acceptable alternative. On decks tall enough to require guardrails, they must still be installed behind the benches, rising to the minimum 36 inches above the decking surface.
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Minimum Strength for Guardrails and Balusters
Guardrail strength requirements: The International Building Code mandates that guardrails must be able to sustain a 200-pound force at the mid-span between posts, without excessive deflective.
Baluster strength requirements: Balusters and in-fill rails must sustain a minimum testing force of 125 pounds over a 1-square-foot area.
Strength of guardrails and balusters is usually simply estimated by a building inspector who will lean or push against the components. In commercial applications, this may be done by an independent third-party testing agency with equipment that applies force up to 500 pounds as a safety margin.