Spot the Violation

FramingStairs, guards & handrailsLevel 32018 IRC

Finished basement stair under a duct soffit

Looking up a carpeted basement stair from the floor of a finished basement. The stairway has painted drywall on both sides and a round wood handrail on metal brackets along the left wall. A drywall soffit boxing in a heating duct crosses the stairway low over the bottom step. Three tape measures are in place: one hangs from the bottom of the soffit to the nosing of the first tread and reads 81, one runs up from a tread nosing to the top of the handrail and reads 36, and one stands on a tread against the riser above and reads 7 1/2. The treads are carpeted over a slight nosing, a framed print hangs on the right wall, and a door is at the top of the stair. 81 36 7 1/2
Finished basement, stair to the main floor

What's wrong here?

  1. Nothing. This installation is compliant
  2. The soffit is too low; stair headroom must be at least 7 ft
  3. The handrail must be 38 in. or more above the nosings to match the guard height
  4. 7-1/2 in. risers are too tall for a basement stair; the limit is 7 in.
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Show the answer and the code reference

The answer

Nothing is wrong: the risers are 7-1/2 in., the handrail is 36 in. above the nosings, and headroom under the soffit is 81 in. (6 ft 9 in.), all within the IRC limits.

Correct choice: 1. Nothing. This installation is compliant

Headroom is measured vertically from the sloped line through the tread nosings, and R311.7.2 requires at least 6 ft 8 in.; this soffit clears the first-tread nosing by 6 ft 9 in., tight but legal. Risers of 7-1/2 in. are under the 7-3/4 in. maximum in R311.7.5.1, and the treads (10-1/4 in. nosing to nosing, with about a 1 in. nosing, as R311.7.5.3 requires for treads under 11 in. with solid risers) meet the 10 in. minimum in R311.7.5.2. The handrail at 36 in. sits inside the 34 to 38 in. range of R311.7.8.1, runs the full flight and is a round Type I rail on brackets. The stair looks cramped, but every measured dimension passes.

How to fix it

No correction needed. When finishing a basement, check that new soffits, ductwork and drywall keep 6 ft 8 in. above the nosing line along the whole flight and that added carpet pad or flooring at the bottom does not shrink the first riser so risers vary by more than 3/8 in.

Code references

  • IRC 2018 R311.7.2 — Headroom

    The minimum headroom in all parts of a stairway is 6 ft 8 in., measured vertically from the sloped line adjoining the tread nosings or from the floor surface of a landing or platform.

    Drills citing R311.7.2

  • IRC 2018 R311.7.5.1 — Risers

    Maximum riser height is 7-3/4 in., measured vertically between the leading edges of adjacent treads; the greatest riser in a flight may not exceed the smallest by more than 3/8 in.

    Drills citing R311.7.5.1

  • IRC 2018 R311.7.5.2 — Treads

    Minimum tread depth is 10 in., measured horizontally between the vertical planes of the foremost projection of adjacent treads; the greatest tread depth in a flight may not exceed the smallest by more than 3/8 in.

    Drills citing R311.7.5.2

  • IRC 2018 R311.7.8.1 — Height

    Handrail height, measured vertically from the sloped plane adjoining the tread nosings, must be at least 34 in. and not more than 38 in.

    Drills citing R311.7.8.1

2024 IRC:renumbered to R318.7.2. The 2024 IRC moved stairways from R311.7 to R318.7 (headroom R318.7.2, risers R318.7.5.1, treads R318.7.5.2) and handrails to their own section (secondary sources say R320); the 6 ft 8 in., 7-3/4 in., 10 in. and 34 to 38 in. figures are unchanged in the sources found. Not checked line by line against the printed 2024 IRC. Confidence: low

Minnesota

MN status unverifiedConfidence: medium

Minnesota adopts the 2018 IRC with Minnesota amendments as the Minnesota Residential Code (Minn. Rules ch. 1309). Minn. Rules 1309.0311 amends parts of IRC R311; search summaries describe a replacement for R311.7.1 that sets which stairs the section covers and show the same 6 ft 8 in. headroom, but the rule text could not be read to confirm that R311.7.2, R311.7.5 and R311.7.8.1 are adopted as published. No Minnesota change to the headroom, riser, tread or handrail figures 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 soffit is too low; stair headroom must be at least 7 ft. The IRC minimum is 6 ft 8 in. (80 in.) above the nosing line (R311.7.2); 7 ft is a common ceiling-height figure, not the stair headroom rule. 81 in. passes.
  • The handrail must be 38 in. or more above the nosings to match the guard height. Handrail height is 34 to 38 in. above the nosing line (R311.7.8.1); 36 in. is right in the middle. The 36 in. guard figure is a minimum for guards at level walking surfaces.
  • 7-1/2 in. risers are too tall for a basement stair; the limit is 7 in. 7 in. is the commercial (IBC) maximum. The IRC allows risers up to 7-3/4 in. (R311.7.5.1).
Code complianceLevel 3 · Master#stair#headroom#handrail#basement#calibration

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