How to measure on site
- The drop. From the walking surface, measure down to the floor or grade below at the edge and at points out to 36 in from it. Use the greatest of those drops. Above 30 in, a guard is required.
- Guard height on a deck, porch, balcony or landing. Measure from the walking surface straight up to the top of the guard.
- Guard and handrail height on a stair. Stretch a string or straightedge across the tread nosings and measure straight up from that line to the top of the guard or rail.
- Openings. Find the widest gap, often between balusters, under the bottom rail or where the guard meets a post or wall. Enter the largest ball that would pass through it. On a stair, also measure the triangle formed by the riser, the tread and the bottom rail.
- Risers. Count the risers in the flight. A flight with 4 or more needs a handrail on at least one side.
The tool compares each number with one limit and shows how much it has to spare or how far it misses. These are comparisons, not code text. The limit values and section numbers are cited so you can find them in your own code book; read the full sections there, including their exceptions.
Which sections, in which edition
The tool checks both editions at once and shows each one's section number in its own column. The 2024 IRC reorganized Chapter 3: guards and window fall protection moved from Section R312 to Section R321, and the handrail details moved out of the stairway section into their own section, R320. The base values this tool uses are the same in both editions.
- Where a guard is required: R312.1.1 in the 2021 IRC, R321.1.1 in the 2024 IRC.
- Guard height, including stair guards and a guard top that serves as the handrail: R312.1.2 and R321.1.2.
- Guard opening limits, including the stair and triangle openings: R312.1.3 and R321.1.3.
- Handrail on flights of 4 or more risers: R311.7.8 and R318.7.8.
- Handrail height: R311.7.8.1 and R320.2.
Bring the numbers for the edition your exam uses. The 2021 vs 2024 IRC guide lists the other Chapter 3 moves.
Worked example: a deck 4 ft above grade
Invented numbers. A deck surface is 48 in above grade within 36 in of its edge. The guard is 36 in tall from the decking, and the widest baluster gap passes a 3 3/4 in ball.
- Guard required: 48 in is 18 in over the 30 in trigger.
- Guard height: 36 in against a 36 in minimum, meets with 0 in to spare. Measure at several posts; a sagging rail or a raised deck board can drop it below.
- Opening: a 3.75 in ball is smaller than the 4 in sphere, meets with 0.25 in to spare.
Worked example: an open-sided porch stair
Invented numbers. A porch stair has 5 risers and an open side 35 in above grade at its high end. The stair guard is 33 in above the nosing line, its baluster gaps pass a 4 1/2 in ball and a separate handrail is 36 in above the nosing line.
- Guard required: 35 in is 5 in over the 30 in trigger.
- Guard height: 33 in against a 34 in minimum on the open side of a stair, 1 in short.
- Opening: a 4.5 in ball against the 4.375 in (4 3/8 in) stair sphere, 0.125 in too wide.
- Handrail: 5 risers is 4 or more, so one is required, and 36 in sits inside the 34 to 38 in range with 2 in to spare at each end.
A deck exactly 30 in above grade needs no guard by the base code, because the trigger is more than 30 in. These are original examples, not exam questions.
What this tool does not check
It does not check guard or handrail loads and attachment, handrail grip size, continuity, returns or wall clearance, the exceptions for volutes, turnouts and fittings, window fall protection, alternating tread devices or ship's ladders. For stair risers, treads, headroom and width, use the IRC stair check. For the difference between the two parts, read guard vs handrail.
Guard and handrail questions
When does a deck or porch need a guard?
When the drop from the walking surface to the floor or ground below is more than 30 in anywhere in the first 36 in out from the open edge. That is R312.1.1 in the 2021 IRC and R321.1.1 in the 2024 IRC. Measure the greatest drop in that band, not only straight down at the edge, because grade often falls away from the house.
How is a guard opening checked?
With a sphere, not a ruler on one gap. Find the largest ball that passes through any gap below the height the guard has to reach and compare it with the sphere size for that spot: 4 in for most guards, 4.375 in (4 3/8 in) on the open side of a stair and 6 in for the triangle under the bottom rail of a stair guard. An opening the sphere fits through does not meet the limit, so the tool treats an opening equal to the sphere as too wide.
Can I use this to pass or fail a real guard?
No. For study and plan-review practice only. The adopted, locally amended code and the authority having jurisdiction (AHJ) decide whether a guard or handrail passes. Local amendments change these rules in some places, and this page does not check guard loads, attachment or the exceptions in each section.
Guards and handrails on the B1 exam
Stairs, guards and handrails sit in the public-safety area of the ICC Residential Building Inspector (B1) outline. Questions usually give a height, a gap or a drop and ask whether it complies, so the skill is finding the right section fast in an open-book setting. Practice locating each limit in your edition rather than memorizing it. The B1 exam outline guide shows how the areas are weighted.