The applicable building energy code that determines the minimum insulation requirements for commercial roofs with insulation entirely above the deck in Ohio is the 2017 Ohio Building Code (based on the 2012 International Energy Conservation Code with state-specific amendments). The minimum insulation requirements apply both to new construction and roof replacements on existing buildings.
The minimum requirement for insulation installed entirely above the roof deck is R-25 for all climate zones. This code became effective on January 1, 2017.
Sample roof assembly diagrams and additional information can be found in PIMA’s Ohio code fact sheet.