Roofing systems and methods

A method for fabricating roofing boards, the method comprising:

• providing a production line configured for continuous fabrication of polymer or predominantly polymer roofing boards by setting and expansion of precursor materials on a conveyor;
• dispensing to the production line a first polymer or predominantly polymer material foam precursor;
• allowing the first foam precursor to rise and at least partially set to form a foam core layer for an insulation board, the foam core layer for the insulation board having a first density;
• dispensing to the production line a second polymer or predominantly polymer material foam precursor;
• allowing the second foam precursor to rise and set to form a core layer for a cover board, the foam core layer for the cover board having a second density greater than the first density;
• and
• setting the combined thickness of the foam core layer for the insulation board and the core layer for the cover board by constraining the expansion of the combined foam precursors using a downstream forming conveyor disposed above the rising foam precursors and positioned downstream of the dispensing of the second polymer or predominantly polymer foam precursor.