Stacked walls allow the use of subwalls with different thickness stacked on top of each other.
This video demonstrates the following:
There are 3 kinds of wall families in Revit: basic walls, curtain walls, and stacked walls. Curtain walls are defined as a system of grids and panels. A basic wall is a wall made up of layers of material from exterior to interior. Basic walls are the same thickness from the bottom to the top. Stacked walls are made up of basic walls stacked on top of one another, allowing you to have walls that vary in thickness from bottom to the top.
In this example, the exterior walls of this building are made from basic walls that have 2 different finishes on the top and bottom. As an alternate to the design, create a stacked wall to instead create a CMU water table on the lower section of the wall.
In the Project Browser, locate a stacked wall type. All walls are system families, so they can't be loaded from an external library. To create new ones in a model, you have to duplicate and alter an existing type. Right-click the stacked wall and select Type Properties.
In the Type Properties dialog, click Duplicate to create a new stacked wall type, and provide a name. Click Edit on the Structure parameter. In this dialog, basic walls are defined from the bottom to the top of the wall. In this example, 2 walls will be used: Exterior - Block Watertable will be set on the bottom and go up 3000mm, the top wall will be Exterior - EIFS set to Variable. Variable means the height of this section will depend on the height of the wall. In the preview window, you can see the stacked wall. Stacked walls can contain any number of basic walls from the bottom to the top. Click OK 2 times to create the stacked wall type.
Select the exterior walls of the building, and on the type selector, choose the new stacked wall type. Zoom in to see the new wall type or examine the wall's section view to see how the stacked wall has different thicknesses on the top and bottom.
Stacked walls can be used to add detail in your models and allow you to create a wall with varying thickness from the bottom to the top.