Spot the Violation

FramingStairs, guards & handrailsLevel 32018 IRC

Foyer balustrade at the upper hall

A two-story foyer seen from the side. A stair with stained oak treads, white risers and a white cut stringer rises from the left to an upper hallway. An oak handrail on white square balusters runs up the open side of the stair, two balusters per tread, to a white box newel post at the top, and continues level along the open edge of the upper hallway as a guard on the same white balusters. A tape measure is hooked on one baluster of the hallway guard with its blade laid across the opening to the next baluster, reading 4 1/4. A framed picture hangs on the stairwell wall, and a bedroom door is visible in the upper hall. 4 1/4
Two-story foyer, stair and upper hallway balustrade

What's wrong here?

  1. The hallway guard has 4-1/4 in. gaps between balusters, so a 4 in. sphere passes
  2. The hallway guard must be at least 42 in. high
  3. Guards at a stair may have openings up to 4-3/8 in., so 4-1/4 in. is fine on the hallway too
  4. Nothing. This installation is compliant
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Show the answer and the code reference

The answer

The balusters along the level upper hallway are 4-1/4 in. apart; R312.1.3 requires guard openings that will not pass a 4 in. sphere there.

Correct choice: 1. The hallway guard has 4-1/4 in. gaps between balusters, so a 4 in. sphere passes

R312.1.3 says required guards may not have openings, from the walking surface up to the required guard height, that pass a 4 in. sphere. Exception 2 relaxes that to 4-3/8 in. only for guards on the open sides of stair treads, and exception 1 allows the triangle under the bottom rail at a stair to pass up to a 6 in. sphere. The level hallway guard gets neither exception. Builders often lay out the whole balustrade to one spacing that works on the stair, and the level run ends up a little too open; a small child's head and chest can pass through 4-1/4 in. and the drop here is a full story.

How to fix it

Re-space the balusters on the level run (or add balusters) so the clear opening is under 4 in.; with 1-1/4 in. balusters, a 5 in. on-center spacing gives 3-3/4 in. clear. Check the stair section separately against the 4-3/8 in. limit.

Code references

  • IRC 2018 R312.1.3 — Opening limitations

    Required guards may not have openings from the walking surface to the required guard height that allow passage of a 4 in. sphere. Exceptions: the triangular openings at the open side of a stair formed by the riser, tread and bottom rail may not pass a 6 in. sphere, and guards on the open sides of stairs may not have openings that pass a 4-3/8 in. sphere.

    Drills citing R312.1.3

  • IRC 2018 R312.1.2 — Height

    Required guards at open-sided walking surfaces must be at least 36 in. high, measured vertically above the adjacent walking surface or the line connecting the tread nosings; on the open sides of stairs a guard may be 34 in. high measured from the nosing line.

    Drills citing R312.1.2

  • IRC 2018 R312.1.1 — Where required

    Guards are required along open-sided walking surfaces, including stairs, ramps and landings, located more than 30 in. above the floor or grade below at any point within 36 in. horizontally of the open edge.

    Drills citing R312.1.1

2024 IRC:renumbered to R321.1.3. The 2024 IRC reorganized Chapter 3; secondary sources place guards at R321, with the 4 in. sphere rule at R321.1.3 and the same stair exceptions. Not checked line by line against the printed 2024 IRC. Confidence: low

Minnesota

MN adopts this rule as writtenConfidence: medium

Minnesota adopts the 2018 IRC with Minnesota amendments as the Minnesota Residential Code (Minn. Rules ch. 1309). No Minnesota amendment to R312.1.3 is known. DLI is adopting the 2024 IRC as the next edition; see the 2024 IRC note.

About the Minnesota Residential Code

Why the other choices are wrong

  • The hallway guard must be at least 42 in. high. 42 in. is the commercial (IBC) guard height. A dwelling guard under the IRC must be at least 36 in. high (R312.1.2).
  • Guards at a stair may have openings up to 4-3/8 in., so 4-1/4 in. is fine on the hallway too. The 4-3/8 in. allowance in R312.1.3 is only for guards on the sides of stair treads. A guard along a level floor, landing or hallway is held to the 4 in. sphere.
  • Nothing. This installation is compliant. A 4 in. sphere passes through 4-1/4 in. gaps in the level guard, which R312.1.3 does not allow.
Safety hazardLevel 3 · Master#guard#balusters#4 in. sphere#landing

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