Building code requirements for exterior decking railing, guards, and stairs are especially stringent because they fall into the category of critical health and safety matters. Code requirements for bathroom fans or drywall might be important but are not a life and death matter. By contrast, deck code is truly a matter of life and death or at least serious injuries. 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 the result of structural failure or collapse.
It pays to keep on top of deck code because it is continually changing. For example, your deck may have toe-nailed connections. If so, be advised that toe-nailing is no longer an accepted connection, per current International Building Code (IBC), though older decks may be grandfathered in. High-profile deck collapses that result in fatalities typically prompt calls for a fresh look at decking code.
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Deck Guardrails: Height and Necessity
The minimum deck guardrail height is 36 inches above deck level. Since this is only a minimum required height for residential structures, higher guards are acceptable. Commercial deck guards, such as those found at restaurants, bars, and at multifamily homes such as apartments or condos, are required to be 42 inches high, minimum.
Some decks are not required to have guardrails, as long as those decks are 30 inches above grade or lower. If you see a deck that has no guardrails (also called a low-rise deck), this might be the reason: its height remains below 30 inches.
If you decide to construct a guard on a deck low enough that it doesn't require guards, it is up to you as to guardrail height and baluster spacing. However, these guards still must be as strong as guards located on higher decks. It is understood that people will lean against guards, and code requires that these guards not collapse, even though only minor injuries would result.
Even with very short low-rise decks, many homeowners still opt to construct guardrails. While a 12-inch drop will rarely prove to be fatal or result in serious injury, it still can twist an ankle or injure a lower back. Adding a guardrail is an inexpensive hedge against injuries such as these.
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Deck Stairs: Rail Height and Stair Treads
Stair rails for decking should be between 34 inches and 38 inches high. This is 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. The rise, or the vertical distance from one tread to the next, can be no more than 7 1/4 inches high.
Stair treads must sustain a weight of at least 300 pounds in an area no more than 4 inches square.
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Deck Balusters and Benches
- 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. Because small children are tempted to stick their heads between balusters (and get them lodged in place), the "four-inch rule" is designed to prevent this from happening.
- Benches: Many homeowners are concerned about preserving the view from their decks and they wonder if benches are acceptable substitutes for deck guards. Unfortunately, they are not. Guards must be installed behind benches, though they do not have to be higher than other guards on the deck.
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Guardrails and Baluster Infill: Minimum Strength
- Guardrails: The International Building Code states that, at a bare minimum, guards must be able to sustain a 200-pound force. In other words, imagine a strong person pushing horizontally against the railing. The railing must be able to sustain 200 pounds of force. However, it is important to note that, from a testing standpoint, the guardrail must sustain 2 1/2 times the minimum force. So, really the guardrail must be able to sustain 500 pounds of force.
- Balusters: Balusters and in-fill rails must sustain a minimum of 50 pounds or a minimum testing force of 125 pounds.