IBC Chapter 15 covers what goes on top of the building. Roof coverings carry a fire classification — Class A, B, or C (1505) — with the required class tied to construction type and, in some jurisdictions, wildfire exposure. The chapter also governs roof coverings and underlayment, flashing and drainage, and rooftop structures: penthouses (1510), which are limited in height and area and generally not counted as a story, plus towers, spires, and rooftop equipment screening.
The common mistake is a penthouse that exceeds the height/area limits and therefore counts as an additional story — quietly blowing the building's allowable height — or a roof covering whose fire class doesn't match the construction type. Reviewers check the roof classification against construction type and confirm penthouses and rooftop structures stay within their limits, because a mislabeled penthouse can cascade into a height-and-area violation that's expensive to unwind.
This guide describes the model code for general understanding and is not a substitute for the adopted code and amendments enforced by your local authority having jurisdiction. Verify all figures against your jurisdiction's codes of record.