The membrane covers the floor substrate and continues up the wall: where the shower has a hob or step-down, the higher of 150 mm over the finished floor tiles and 25 mm over the level at which the shower would overflow (maximum retained water level); where it is hobless, 150 mm over the highest point of the finished shower floor tiles. In shower areas junctions are treated to the higher of 1 800 mm over the finished floor and 50 mm over the rose (4.11.2); with a ceiling-mounted rose, the junctions are treated to the full wall height with a Type 3 junction.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.