The applicable building energy code that determines the minimum insulation requirements for commercial roofs with insulation entirely above the deck in Pennsylvania is the 2015 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-30 for all climate zones. This code became effective on October 1, 2018.
Sample roof assembly diagrams and additional information can be found in PIMA’s Pennsylvania code fact sheet.