Abstract: An interior roof gutter system intended for use on certain large non-residential buildings on which stormwater flows to low elevation perimeter walls. Whereas such walls frequently present a vertically extended parapet, the present invention discloses a novel interior gutter system. The gutter system is preferably composed of fiberglass reinforced polyester, or similar material. The gutter system is comprised of a plurality of rigid independent, elongated, trough-like, monolithic modules. When installed in tandem, with a non-impinged connection, expansion and contraction forces are accommodated. The present invention provides for attachment and flashing to the parapet wall on one of the elongated module walls, and attachment and flashing under the roof membrane on the opposite module wall. To prevent ice formation from blocking normal drainage in freezing climates, a melting device is presented.