Abstract: An air-conditioning condensate drainage system for mounting to the roof membrane of the roof structure of buildings or for constructing directly onto the roof membrane of a building structure. The air-conditioning condensate drainage system has an isolation membrane having a bottom surface for assembly to a roof membrane. A pair of ridge structures are disposed in fixed relation with the isolation membrane and are disposed in spaced relation with one another and cooperate with the isolation membrane to define an air-conditioning condensate drainage channel between the spaced ridge structures. Each of the ridge structures has one or more ridge defining elements which is fixed to the isolation membrane and projects above the isolation membrane sufficiently to define a condensate drain channel therebetween.