N.M. Code R. § 14.7.2.14
See this chapter of the IBC except as provided below. Section 603 - Combustible Material in Types I and II Construction. See this section of the IBC except as provided below. Section 603.1 - Allowable materials. Add the following exceptions to subsection 2:Exception 28. Stairways within individual dwelling units and stairways serving a single tenant space are permitted to be of fire-retardant wood or heavy-timber construction. In other than Group R occupancies, such stairways shall not serve as a required means of egress. Exception 29. Stairways complying with section 510.2, item 4 permitted to be constructed of wood above the horizontal assembly are also permitted to be constructed of wood below the horizontal assembly.
N.M. Code R. § 14.7.2.14