Abstract: A slate roofing material joint having a flat strip-shaped mounting base plate made of weatherproof soft resin. A pair of flat-based plates, which are also weatherproof, but are made of hard resin, are connected to the sides of the mounting base plate. Several water-guide protruding strips run along the base plates and edge flashings made of weatherproof soft resin are formed at the outer edge of the base plates. A portion of the edge flashings are bent upward and curved inward with an edge thickness that progressively declines for elastically supporting roofing material. The entire structure forms an integral unit made of weatherproof soft and hard resins for carrying away water, which has seeped through the roofing material, out from under the roofing material.