I've been looking around the internet, and I've seen quite a few stair renovations using common boards with a square edge rather than bull nose stair treads.

Is there a difference between the two beside looks?

Code, wear and tear? The common boards are definitely less expensive and have a larger stock to choose appealing boards from when I buy.

1 Answer 1


The building code does address the width, profile, and the rounding of the treads.

From the 2009 IBC:

R311.5.3.3 Profile. The radius of curvature at the leading edge of the tread shall be no greater than 9/16 inch (14 mm).

I believe the reason for rounding the leading edge of the tread with wood is to reduce the likelihood of splintering. Also, standard soft pine building lumber is more likely to warp or be damaged with use than a hardwood stair tread.

Good luck with your project.

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    For clarity - a larger radius is more rounded. Hence a code specified maximum radius does not preclude having no radius at all, i.e. a square edge would not violate the quoted clause.
    – AndyT
    Commented Jan 26, 2016 at 9:21
  • 1
    But the square edge is going to get roughed up quickly on a stair tread.
    – Michael Karas
    Commented Jan 26, 2016 at 15:10
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    And really square edged don't hold a finish or take well to carpeting or other tread covers. Finally, for us foot-draggers, they may also catch a brushed heel, which a rounded edge is less likely to do.
    – bib
    Commented Jan 26, 2016 at 15:27
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    @AndyT: Mathematically, the larger the radius, the less rounded. An infinite radius circle is a straight line... Now are the drafters of building codes mathematically literate??
    – DJohnM
    Commented Jan 27, 2016 at 1:40
  • @DJohnM - Yes, the drafters are mathematically literate. An infinite radius, causing a straight line, would mean that the tread had only a horizontal plane, and no vertical face to it at all. The drafters have precluded this - sensible people. I will grant you that "more rounded" and "less rounded" are not exact terms, perhaps you would prefer "a larger radius means a larger part of the tread is curved; hence a maximum radius does not preclude having no radius at all, i.e. no part of the tread being curved, i.e. a square edge"?
    – AndyT
    Commented Jan 27, 2016 at 9:06

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