A guard is nothing more than a barrier to block a human body from a fall from an elevated walking surface. It does not require any type of rail or graspable feature. The word "guard” should be used to describe that barrier.
The image above shows a guard supported by balusters. Guards should be supported by posts every 6 feet.
A handrail requires a graspable rail. That's what a handrail is. It is a graspable thing. They're installed next to certain stairs and ramps. And sometimes they're built into the top of the guard.
Guard Load Connected to Joist
Where guards are supported on deck framing, guard loads must be transferred to the deck framing with a continuous load path to the deck joists. The guard must connect to the floor joist, not the outer rim or band joist.
Where guards are connected to the interior or exterior side of a deck joist or beam, the joist or beam shall be connected to the adjacent joists to prevent rotation of the joist or beam. If the guard is connected along the exterior joist, it must be connected to an adjacent joist. Otherwise, the single joist connection will rotate and won't support the guard above adequately. Connections relying only on fasteners in end grain are not permitted.
Where guards are mounted on top of the decking, the guards must be connected to the deck framing or blocking and installed in accordance with the manufacturer’s instructions to transfer the guard loads to the adjacent joists. The guard must connect to the framing or blocking to transfer the load to the adjacent joists.
Where 4-inch by 4-inch (102 mm by 102 mm) wood posts support guard loads applied to the top of the guard, those posts must not be notched at the connection to the supporting structure. For wooden posts at deck guards, the posts must not be notched at the connection to the deck structure.
The image above depicts a notched-deck guardrail post attachment. This common notched-type of attachment was permitted by most older codes. It is no longer permitted. Notched posts are a defect. The building standard changed in 2021. Refer to 2021 IRC R507.10. Notched guard post attachments could become loose and unsafe, especially as the deck ages.
The 2021 IRC code specifically prohibits notched 4x4 guard posts at the connection point, which historically have been attached to rim joists or beams with anything from lag screws to nails.
Code now requires that the connection extend back into the framing in some manner to help prevent a guard from pulling a rim joist off the ends of the joists or from rotating a single side joist.
Loads and Forces in Directions
While graspable stair handrails are meant to support us and must resist forces in all directions, guards that wrap around a deck are only meant to keep us from falling off the edge.
According to the 2021 IRC code, guards will no longer be required to resist forces pulling inward or upward. Just outward.
Leaning on or sitting on top of a guard is common, so a guard must be able to support the load. Guard and handrail design loads are separate and different. The load direction for guards and handrails is also different. There is also a difference between uniform and concentrated loads.
The 2021 IRC Table R301.5 recognizes the differences between guards and handrails. The code separates them from each other and provides a separate column for concentrated loads.
The concentrated load direction for guards and handrails in the IRC before 2021 was in “all directions.” The 2021 IRC Table 301.5 changed the loading direction for guards to only outward and downward directions. Guards: a concentrated load of 200 psf (pounds per square foot) outward and downward.
If the top of a guard is NOT serving as a required handrail, the single concentrated load could be applied at any point along the top, in the vertically downward direction and in the horizontally outward direction away from the walking surface.
Where the top of a guard IS serving as the handrail, a single concentrated load could be applied in any direction at any point along the top. So, inspectors should really wiggle those handrails.
While handrails are graspable and can be pulled in any direction, a guard is NOT required to be pulled or pushed in any direction. Just down and out. A guard has no reason to resist a fall backward or to resist a load placed in line or upward.
Because of leverage, a 200-pound force pushing the deck's guard outward causes a 1,700-pound force at the upper bolt attaching the post. It is difficult to attach deck guard posts in a manner that is strong enough without using deck guard post brackets.
The image above depicts a deck guard post properly attached with brackets.
Decks that are greater than 12 inches above adjacent areas should have guards around the edges. Some codes require guard only around the edges of decks 30 inches or higher.
Guard Height & Openings
Most residential codes require the top of the guard to be at least 36 inches from the deck surface. Most commercial code height is 42 inches.
The image above depicts child-unsafe guard infill. Infill should not permit a 4-inch sphere to pass through.
The image above depicts horizontal balustrades. Ladder-type guard infill on high decks is prohibited by some local codes because they are easy for children to climb over.
The illustration above depicts a post and balusters cut level and not shedding water. The end-grain of vertical posts and balusters should not be cut level.
The illustration above depicts a post and balusters properly cut at angles to shed water. The end-grain of vertical posts and balusters should be cut at an angle.
Stringers, Risers and Treads
The illustration above depicts a deck stair stringer. Stair stringers shall be made of minimum 2x12-inch lumber, and no less than 5 inches wide at any point.
The illustration above depicts deck stair stringers. Stringers should be no more than 16-18 inches apart for wood decking and 12 inches for composite.
The number of stringers installed at a wood-framed stairway is related to the 36-inch minimum width. If cut stringers are used in the stair construction, then at least three stringers are required. Cut stringers should be spaced no more than 18 inches on center. For example, a 36-inch-wide stairway would have three stringers.
If the stairway is wider than 36 inches, four stringers should be installed. If the stairs are wider than 36 inches (914 mm), the maximum spacing between the stringers should be 18 inches (457 mm) on center. The maximum 18-inch spacing works well with treads made of 2x boards or 5/4-inch boards.
The illustration above depicts ledger strips properly located under stair treads. Where solid stringers are used, stair treads should be supported with ledger strips (as depicted), mortised, or supported with metal brackets.
The illustration above depicts a set of stairs with open risers. Most deck stairs have open risers and are not safe for children. Risers may be open but should not allow the passage of a 4-inch diameter sphere.
The illustration above depicts stair riser height. To minimize tripping, the maximum variation among riser heights (the difference between the tallest and shortest risers) should be no more than 3/8-inch.
The bottom step of a stairway leading up to a deck is typically at a different height than the rest of the steps. This can present a trip hazard.
Steps with open risers can present a tripping hazard if a user catches his foot by stepping too far into the tread. To mitigate this hazard, the risers can be closed or the treads can be made deeper.
Information used with permission of nachi.org