The shower installation kit includes an elongated drain adapted to be arranged at an inclined shower floor and at least one elongated side member adapted to be arranged at right angles to the elongated drain and at a side of the inclined shower floor. Each elongated side member has a longitudinal flange adapted to define a slope of the inclined shower floor and adapted to be positioned under a floor covering of the inclined shower floor. The drain is adapted to be mounted at a distance from a subfloor structure of the inclined shower floor before installation of the inclined shower floor. The drain is provided with a front flange adapted to be positioned under the floor covering, and the longitudinal flange of the at least one side member is connected to and arranged flush with the front flange of the drain.