Reverse floating walls in basement construction

When working in expansive soils such as clay and other soils that expand with moisture content, special precautions must be taken to prevent structural damage to foundations and basement walls. One of these precautions is floating walls. A floating wall is not joined at the top and bottom like most walls. A floating wall can move with the house and prevents cracks from opening in the floor, foundation, and walls as the moisture content in the soil changes.

Floating basement walls are usually attached to the first floor floor joists and then nailed into the floor to provide a gap under the wall. This space is covered by the baseboards and cannot be seen.

A reverse floating wall is attached to the floor. You lay the flooring on the base plate on the floor and nail it at the top so the wall is stable but only attached at the bottom. This is done on wet walls to keep the pipe stable. The open space is at the top of the walls and is covered by moldings. You can cover the entire wall with drywall, but be careful to leave the top open for movement. This means you can’t attach the drywall to the wall all the way to the top or it will crack as the wall moves with moisture changes in the ground.

For reverse floating walls, follow the basic instructions for floating a wall, but instead of hanging the wall from the floor joist, you’ll adhere the floor to the base plate and the spike to the top plate. Make sure your wall is plumb. If you don’t have an exactly square wall, it will bring you problems. A 4 ½-inch gap is needed at the top of the wall. The wall also needs to be nailed in the same way as a normal floating wall, just at the top instead of the bottom. See floating wall instructions for more information.

To cover the open area at the top of the wall, you can use trim. Many people don’t like the look of the trim around the ceiling. If you want alternatives, you may want to consider having a drop ceiling that can move with the walls and floor. You would have to attach the roof frame to the wall frames. When the house breathes your whole room will move and you won’t notice it.

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