Way back in 2012 when the first wall was about to be taken down, I took this photo of the floating wall in the master bathroom.
A floating wall is not fully connected between the ceiling rafters and the floor of the house. In areas of expansive soil, the walls are not allowed to create a solid plane that could push up against the rafters when the floor heaves. The roof could become warped and the house pushed out of alignment. A gap is created between either the top or bottom plate and a second plate is connected to its base with long nails that can take the pressure and allow the wall to slide along them as the floor heaves or falls.
Interestingly in this photo some of the worst floor cracking had occurred. I sure didn’t notice when admiring the house to purchase it, but the inspector pointed out the big drop in this corner. A large crack is seen under the floor brush in the foreground and it goes through the wall, where the 2 x 4 is cracked and through the linoleum. The shower pan has dropped away from the back wall and there is a large crack at the perimeter behind and beside the toilet. So it is a good thing this house had floating walls!
Although the bottom plate is partially obstructed by the drywall debris in the photo, there is a gap between it and the 2 x 4 above it. This gap appears to be less than the 1 1/2″ that is required now, but it could be that the gap changed over time as the floor heaved and fell.
In areas subject to floor heaving, non-bearing walls on basement floor slabs should be built to accommodate not less than 1-1/2 inches of floor movement.
The finish detail shows pressure treated floor plates, however our floor is not below grade so we are using the original 2 x 4 base. This specification mentions 40 lb nails for the walls to slide on. It also shows that drywall does not extend to the bottom plate but a spacer is installed instead, supposedly covered by the baseboard.
The floating or hanging walls are more secure than you might believe since they are only held vertical by a few long nails. We have just started our walls and Dave has developed a method he is comfortable with that is very sturdy.