It’s not easy to remember every code requirement, especially when you don’t build stairs often! Here’s an easy-to-access and easy-to-understand illustrated version of the 2009 IRC code as it applies to stairs.
For a stair to pass inspection, these code requirements are critical. But, these requirements are also critical if you want to build a safe, easy-to-use stair.
Railing height gets confusing. Here’s a simple illustration. But remember, the bottom newel post in this illustration isn’t legal! The railing must be continuous to a point plumb with the bottom riser.
Many carpenters think that the “4 in. sphere rule” applies to every space on a balustrade. Not true! The balusters on a guard rail must be close enough so that a 4-in. sphere cannot slip through. But the balusters on a raked handrail can be spaced wider; and the spandrel space between the bottom rail and the tread can allow for a 6-in. sphere.
And don’t forget to check the head height! To meet IRC Code, there must be 80 in. clear, measured plumb from the nose of the tread to any obstruction above (floor, coffered ceiling, beam, etc.).