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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 for creating comfortable and code-compliant stairs that will serve your home for decades.

Understanding Stair Terminology

Total Rise: The total vertical distance from the finish floor below to the finish floor above. This is the most critical measurement as it determines how many steps your staircase will need. Always measure from finished floor to finished floor, not from subfloor to subfloor.

Total Run: The total horizontal distance covered by the staircase. This measurement affects how much floor space your stairs will occupy and should be planned carefully, especially in renovations where space may be limited.

Riser: The vertical portion of a step. Open risers are permitted in some jurisdictions but typically closed risers are standard for safety reasons. The riser height is crucial for comfort and code compliance.

Tread: The horizontal part where you place your foot. This must meet minimum depth requirements and often includes a nosing that extends slightly beyond the riser below for added safety and comfort.

US Building Code Guidelines (IRC)

The International Residential Code (IRC) dictates the standard for safe stairs in the US. These codes have been developed over decades of research into stair safety and comfort, and adherence to them is not optional—it is required by law in virtually all jurisdictions. Key requirements include:

• Maximum Riser Height: 7.75 inches (196 mm). This ensures stairs are not too steep to climb safely.
• Minimum Tread Depth: 10 inches (254 mm). This provides adequate foot placement area for safe descent.
• Minimum Stair Width: 36 inches (914 mm). This allows for comfortable passage and furniture moving.
• Minimum Headroom: 6 feet 8 inches (80 inches / 2032 mm). This prevents head injuries during use.
• Riser variation: No more than 3/8 inch variation between the largest and smallest riser to prevent tripping.

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". This formula has been used by stair builders for centuries to create stairs that feel natural to walk on.

Rise + Run = 17 to 18 inches.

Example: A 7-inch rise paired with an 11-inch run (7+11=18) is considered ideal for residential stairs. Steeper stairs (e.g., 8" rise + 9" run) may be code compliant in older structures but are often uncomfortable and can be challenging for elderly users or those with mobility limitations.