A riser is the vertical part of a stair run that is above and below the treads that you walk on. The International Residential Code (IRC 1011.5.5.3) allows open risers as long as “the opening between the treads does not permit the passage of a 4-inch diameter sphere.” The regulation applies to both interior and exterior stairs and the purpose is to avoid getting a foot caught in the open space when turning around or a child being trapped or falling through the gap. 

   Stairs are the most dangerous part of a house, and about 1,400 people die in the U.S. each year as a result of a fall from a stair. Also, just under a million people are hospitalized yearly due to stair falls--over half of them in their own home. Falls are also the leading cause of hospitalizations among children and the elderly.

    So why are there so many pictures in design magazines, like the one above, of stairs that are both elegant and unsafe—often in the trophy homes of the rich and famous? We suspect it is because these high-style stairs are partially deconstructed or reconstructed after the building inspector’s final visit to the house.

    The code does have an exception for a short stair run: “The opening between adjacent treads is not limited on stairs with a total rise of 30 inches or less.” We assume this is because the risk of injury is much less on a stair with just four or five steps. Spiral stairs are also exempt from the solid riser requirement.

   But when designers flaunt the stair safety standards for open risers, they usually go all the way, again like in the photo above, and ignore the 4-inch sphere requirement that also applies to spacing between balusters in a stair railing.

    Also, see our blog posts What is the minimum headroom clearance for stairs? and What is the steepest residential stair allowed?

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Here’s links to a collection of our other blog posts about STAIRS:

• What do home inspectors check when inspecting stairs?

• Is a landing always required at the top and bottom of stairs? 

• When is a railing required at stairs?

• What is the building code for the minimum height of stair steps (risers)? 

• When is a nosing required on a stair tread?

• What is the building code requirement for receptacle outlets at stairs and stair landings?  

• Why is a single step dangerous in a house?

• Do I need stairs at all exit doors from a mobile home? 

• The stairs feel too steep. What's the building code? 

• What is the longest stair run allowed? 

• What is the lighting requirement for stairs?

• A light is required over a stair after how many steps/risers? 

• When is safety glass required for windows at stairs and stair landings?

   Visit our STAIRS page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.