No Terrain under room on piers

[Gary-Doski]

So, besides the "hide terrain intersected by building" check box, and making a custom solid, what other ways have users

got the grass to grow under a room?

[DBCooper]

Try this:

Select the terrain perimeter.

Use the "make terrain hole around building" tool.  This takes the auto generated hole and converts it into a manual terrain hole.

Select the hole and reshape as needed.

[CharlesVolz]

Or, place the terrain on Floor 0 so that cantilevered building areas like boxed windows do not cut a hole in the terrain. Only your foundation walls influence the terrain cut out.