When designing or building a staircase, following the Stair Riser Height Code is critical. This code ensures that stairs are safe, consistent, and comfortable to use. In homes and residential spaces, even a small error in stair riser height can cause tripping hazards or code violations. That’s why every step must follow strict measurements approved by the International Residential Code (IRC) or local building regulations.
Understanding the stair riser height code helps homeowners, builders, and DIY enthusiasts avoid costly mistakes. In this article, we explain everything about stair riser height, run, and nosing, based on the IRC 2021 and updated building code requirements as of 2025.
What Is a Stair Riser?
The stair riser is the vertical part of a stair between two treads. When you step from one stair to another, the riser is what lifts your foot to the next level. The stair riser height code controls how high this part can be to maintain uniformity and safety across the entire staircase.
If one riser is taller than the next, it causes a tripping hazard. This is why the code clearly defines the maximum and minimum allowable riser heights.
IRC Stair Riser Height Code 2025
The International Residential Code (IRC) defines the legal requirements for stair risers in residential buildings. According to the 2021 version of the IRC (still valid in most areas in 2025), the stair riser height code sets the following limits:
| Feature | Measurement |
|---|---|
| Maximum riser height | 7.75 inches (197 mm) |
| Minimum riser height | 4 inches (102 mm) |
| Maximum height variation | 3/8 inch (9.5 mm) |
Each riser must be of the same height within a single flight of stairs. Any change more than 3/8 inch between steps is not allowed.
These measurements are taken from the top of one finished tread to the top of the next. That means you must include flooring materials like tiles or carpets in your measurements.
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Why the Stair Riser Height Code Matters
Safety is the most important reason behind stair riser rules. Uneven steps cause people to lose balance and fall. The stair riser height code protects everyone—from small children to elderly people—from injury.
Another reason is comfort. Climbing stairs with very tall risers is tiring. On the other hand, stairs with very short risers feel awkward and take up too much space.
By following the correct stair riser height code, builders create stairs that are safe, easy to walk on, and efficient in space.
Building Consistent Risers: Common Mistakes
Many mistakes happen when people forget to include finished flooring. For example, if you install tile or carpet after cutting stair stringers, the total rise may go above the limit. This breaks the stair riser height code even if you did all math correctly before installing the stairs.
Another error is using pre-made stair stringers without checking the height. Some of these don’t match the local code.
Always measure the total rise from bottom floor to top floor, divide it by the number of risers you want, and adjust to stay within the legal height range.
Stair Tread and Run Requirements
The tread is the horizontal part of the stair where your foot steps. While riser height is important, you must also follow rules about tread depth (also called “run”).
According to the IRC code:
- If your tread has a nosing (overhang), it must be at least 10 inches deep.
- If your tread has no nosing, it must be at least 11 inches deep.
Like risers, treads must also be consistent. The depth of each tread must not vary by more than 3/8 inch.
Stair Nosing Requirements in 2025
Nosing is the front edge of the stair tread that extends beyond the riser below. The stair riser height code includes details about nosing because it affects the total run.
Here’s what the IRC says about stair nosing:
| Feature | Measurement |
|---|---|
| Minimum overhang | ¾ inch (19 mm) |
| Maximum overhang | 1¼ inch (32 mm) |
| Max nosing radius | 9/16 inch (14 mm) |
You don’t have to use a nosing if you have 11-inch treads. But if you do include it, these rules apply.
Practical Example: How to Calculate Riser Height
Let’s say your total rise from floor to floor is 112 inches. To calculate the correct riser height:
- Divide total rise by 7.5 (a common riser height):
112 ÷ 7.5 = 14.93 ≈ 15 risers - Now divide 112 by 15:
112 ÷ 15 = 7.47 inches per riser
This value fits well within the stair riser height code.
Always round your riser height to keep it under 7.75 inches and above 4 inches, and make all risers equal.
Regional and Local Stair Riser Codes
While the IRC is widely followed in the U.S., local governments may adopt modified rules. In commercial buildings or high-traffic areas, other codes such as the International Building Code (IBC) may apply.
Some cities enforce stricter requirements. For example, California may have accessibility rules that further limit riser height for wheelchair-accessible homes.
That’s why it’s important to always check with your local building office before starting a staircase project.
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Nailing the Code: Installation Tips
To meet the stair riser height code, follow these tips:
- Include the thickness of flooring in your measurements.
- Use a level and straightedge when marking stair stringers.
- Use construction-grade lumber for consistency and durability.
- If you’re unsure, use online stair calculators to do the math.
- Always verify your plan with a building inspector.
Even if you follow the code perfectly, poor installation can lead to mistakes that affect safety.
| Code Element | Measurement | Note |
|---|---|---|
| Max riser height | 7.75 inches (197 mm) | Per IRC 2021 |
| Min riser height | 4 inches (102 mm) | Avoid extremely low risers |
| Max riser variation | 3/8 inch (9.5 mm) | All risers must be consistent |
| Tread with nosing | 10 inches | Horizontal depth |
| Tread without nosing | 11 inches | Minimum depth required |
| Nosing range | ¾ inch to 1¼ inches | Optional but regulated |
| Nosing radius | Max 9/16 inch | Must not exceed this curve |
Frequently Asked Questions
What is the maximum stair riser height allowed by code?
The IRC sets the maximum riser height at 7.75 inches for residential stairs.
\Can stair riser height vary in one staircase?
No. The difference between the tallest and shortest riser must not exceed 3/8 inch.
What happens if I build stairs with risers too tall?
You may fail inspection and have to rebuild the stairs, leading to extra cost and time.
Is nosing required for all stairs?
Nosing is not required if each tread is at least 11 inches deep. If included, it must follow strict limits.
Final Words
The stair riser height code protects your safety and ensures a smooth walking experience. By sticking to the exact measurements for riser height, tread depth, and nosing, you meet building standards and reduce injury risk. Whether you’re building stairs for a new home or remodeling an old one, following these rules is essential.
Make sure to use accurate tools, take finished flooring into account, and get your design approved locally. With careful planning and adherence to the stair riser height code, your staircase will be both legal and safe for years to come.