Giovanni Valle is a licensed architect and LEED-accredited professional and is certified by the National Council of Architectural Registration Boards (NCARB). He is the author and managing editor of various digital publications, including BuilderSpace, Your Own Architect, and Interiors Place.
Many homeowners have to deal with limited space. You may want the stairway to take up the least floor space possible for efficiency. Building steep-angle stairs is one way to preserve space, but you may have a problem if the stairs are too steep.
A slope of 45 degrees is too steep of an angle for stairs in residential buildings. The standard staircase angle is 37 degrees. A stair flight angle of up to 38 degrees is acceptable as it accommodates the minimum riser and run requirements.
The stair angle you choose has a significant impact on the floor space. You must balance code requirements, comfort, and space when building stairs. In this article, I’ll discuss fitting stairs that comply with building codes in a tight space.
How Steep Is Too Steep for Stairs?
It’s normal for homeowners to try to budget their floor space. If you have an upper floor, you’ll worry about installing comfortable stairs while minimizing space.
Many will try to fit stairs in the smallest space possible when the space is tight. The smaller the space for stairs, the steeper the slope angle will need to be.
While shrinking the floor under stairs may serve your interest, stairs can’t be as steep as you wish to save space. Fitting the staircase too tightly can make the installation uncomfortable for some users and breach building codes.
The stairway angle is affected by riser height and run depth measurements, which determine the space you need for the installation. The riser is the vertical part of a step, and the run is the horizontal component.
There’s a range within which riser and run measurements should fit to comply with codes. These are the acceptable riser and run sizes for residential buildings:
Residential Stair Riser Height Range
The widely-used International Residential Code (IRC) requires a maximum riser height of 7¾ inches (20 cm). Although the IRC has no minimum riser height, many stairway installations observe a minimum height of 4 inches (10 cm). Most staircase steps are 7 inches (18 cm) high.
Residential Stair Tread Run Depth Range
The IRC requires a minimum staircase step depth of 10 inches (25 cm). Again, the IRC doesn’t have a maximum tread run depth requirement. As a result, you can install wide, custom stairway steps if you have the space.
To barely comply with the codes, your stairway risers should be 7 ¾ inches (20 cm), and runs should be 10 inches (25 cm). With that, the maximum acceptable staircase angle is 38 degrees.
Achieving a 45-degree slope angle would require setting risers and runs at 7 inches (18 cm) each. With that, you’d comply with the IRC riser code but miss on the run, which must be 10 inches (25 cm) at the very least. As a result, 45 degrees is a too steep angle for stairs to meet code requirements.
Can You Have Unequal Stair Riser Heights?
Step heights can vary slightly, but there’s very little wiggle room. The IRC allows riser height variations up to 0.375 inches (0.95 cm).
Considering the riser-to-run ratio guidelines that architects generally follow when designing stairs, reducing the riser can allow you to increase run depth.
The problem is that the acceptable variation is too small to make a difference. For example, installing stairs with a slope angle of 45 degrees would mean having 7-inch risers and 7-inch runs. Reducing the riser height by about half an inch and expanding the run depth by the same measure would still fall short of the code.
Moreover, unequal staircase step heights can be a severe safety hazard. People climbing stairs need to make consistent steps to maintain the proper balance. As a result, uneven step heights can disrupt the walk, potentially causing people to trip and fall.
Additionally, unequal stairway steps may save you space but adversely impact your home’s resale value. If you plan to sell your home, invest in an excellent stairway installation to protect your property’s value.
What Is the Ideal Angle for Stairs?
The ideal angle for stairs is 37 degrees. A flight sloping at this angle is comfortable, compliant, and efficient. The preferred angle range for stairs is 30 to 37 degrees.
Apart from the stairway angle, headroom is another important consideration when installing stairs. The code requires a minimum headroom of 6 feet, 8 inches (2 meters).
Why Stairway Flight Angle Matters
A steep angle for stairs takes up less floor area, which you may want if you have a tight space. However, high angles are considered uncomfortable for most people and unsafe for elderly people and others with mobility challenges.
A high slope would give narrow runs, resulting in a small surface for people to step on as they walk along the steps. The run span should be large enough to accommodate the foot, providing sufficient support and avoiding slipping and tripping incidents.
A low slope angle allows for a more comfortable climb. Apart from taking up more space, a low angle fits more steps. As a result, low-slope stairs can take more time to climb.
Width is another stairway dimension to watch. It’s another aspect of staircase design that impacts space. The width should be at least 36 inches (91 cm) for single-user stairs.
Codes also require a stairway with a continuous handrail on at least one side. The minimum height of the handrail from the ramp slope should be 34 inches (96 cm). The rail’s maximum height should be 38 inches (96.5 cm)
How to Fit Compliant Stairs in a Tight Space
The ship ladder stair can be an excellent option to fit a stairway in a tight space. This stair design combines the features of a traditional ladder and a conventional stair system.
Ship ladders can be significantly steeper and narrower than standard stairs. For example, codes allow riser heights of up to 9.5 inches (24 cm) for ship ladder stairs. The tread run depth on ship ladders can be as narrow as 5 inches (13 cm).
Moreover, the ship ladder flight width can be as narrow as 20 inches (51 cm). These installations must have handrails on both sides to provide support.
With ship ladder stairs, you can install a comfortable, economical, and compliant 45-degree stairway flight angle. However, the ship ladder stair option has limited application in homes.
A stairway angle of 45 degrees is too steep for residential stairs in conventional installations. With a ship ladder stair, you can achieve a steeper staircase angle and save floor space.
Consider contacting a professional to discuss stairway options for your home if you have tight space.
- Inspectapedia: Stair Angle or Slope Specifications
- How To Look At A House: What Is the Steepest Residential Stair Allowed?
- CDAID.ORG: IRC Code Handout
- Autodesk: Rule-of-Thumb Formulas for Stairs
- Inspectapedia: Stair Step Height FAQs
- MercuryNews: Homefix: You Cannot Sell A House With Uneven Stairs
- Dimensions: Stair Widths
- California Department of Industrial Relations: Stairways
- Building Code Trainer: Are Ship Ladders Code Compliant?
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