Open Riser Building Code Issue
The picture above provides us with an excellent example of stair
treads that are thick enough to prevent a 4 inch round sphere from
slipping past it. 4 inches is the maximum distance any section of a
stairway can have in between the other parts.
For example, 4 inches is the maximum distance allowed in between the top of a lower stair tread and the bottom of the one above it as shown in the picture above. This 4 inch measurement also applies to baluster spacing and for more information, you can check out our list of stair building codes.
Before you design and build an open stairway, it wouldn't be a bad idea to check with your local building department, because some stairways are required to be closed, for a variety of different reasons, including fire and safety.
Closed Stairway Riser Options