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How to Build Safe & Comfortable Stairs
Stair building is both an art and a science governed by strict building codes to ensure safety. Whether you are building a deck staircase, an interior set of stairs, or a basement entry, understanding the relationship between rise, run, and angle is critical.
Understanding Stair Terminology
Total Rise: The total vertical distance from the finish floor below to the finish floor above.
Total Run: The total horizontal distance covered by the staircase.
Riser: The vertical portion of a step. Open risers are permitted in some jurisdictions but typically closed risers are standard.
Tread: The horizontal part where you place your foot. This must meet minimum depth requirements.
US Building Code Guidelines (IRC)
The International Residential Code (IRC) dictates the standard for safe stairs in the US. Key requirements include:
- Maximum Riser Height: 7.75 inches (196 mm).
- Minimum Tread Depth: 10 inches (254 mm).
- Minimum Stair Width: 36 inches (914 mm).
- Minimum Headroom: 6 feet 8 inches (80 inches / 2032 mm).
- Riser variation: No more than 3/8 inch variation between the largest and smallest riser.
The Comfort Formula
Beyond code compliance, a comfortable stair follows a rule of thumb known as the "Rule of 25" or the "17-18 Rule".
Rise + Run = 17 to 18 inches.
Example: A 7-inch rise paired with an 11-inch run (7+11=18) is considered ideal. Steeper stairs (e.g., 8" rise + 9" run) may be code compliant in older structures but are often uncomfortable and steeper than modern standards.