In order to ensure effective water drainage, a gradient needs to be created along the floor to channel the shower water into a drain. The most common method for forming a gradient is to install a sub-floor made from plywood, which creates a “fall” towards the drain.

The wet-area floor needs to slope at least 1/4 inch per foot to send water toward the drain; code also requires that the drain be at least 2 inches below the high point in the floor. If incorporating a wet room in an addition, the floor structure can be built to accommodate the plumbing plan from the beginning.