(A) The board of building standards shall adopt rules governing the number of water closets required to be installed in women’s and men’s rest room facilities in buildings or parts of buildings used for assembly purposes in accordance with the standards specified under a national model plumbing code that is consistent with rules adopted by the board pursuant to division (A) of section 3781.10 of the Revised Code.

(B) For purposes of this section, a building or part of a building is used for assembly purposes when the use of the building or part of a building conforms to assembly usage as adopted by rule under division (A) of section 3781.10 of the Revised Code.