Installing Floating Walls in Basements

Since clay is an expansive soil it can make putting a basement in your home a bit tricky. When putting in internal walls you have to allow for the natural movement your home is going to have as the water content in the soil changes. This movement allows the home to breathe, or move up and down as the ground expands and shrinks with the water content in the clay soil. Floating basement walls will allow for this movement.

Floating walls are basement level partition walls that have been suspended from the floor joists of the first floor. These walls have a space at the bottom that isn’t attached to anything to allow the home to breathe. There isn’t a space open at the bottom of the walls that your cat is going to run through and you aren’t going to lose your favorite sneakers under the wall. Floating walls probably aren’t something most people home owners are aware of because the space is covered with baseboards.

Installing floating walls takes a bit of extra time and care. Floating walls are suspended leaving a 4 ½” space between the bottom of the wall and the concrete floor slab. A base plate is attached to the floor and the base plate and the wall have to be precisely vertical. It is imperative that the wall is plumb.

To install floating walls and make sure they are precisely vertical you need to put down the base plate but do not nail it in place. To obtain measurements for the floating walls you need to measure the space from the top of the base plate to the bottom of the floor joists.
It will take two people to measure and install floating walls. While standing on the base plate use a 6’ level and a straight 2X4 stud and holding the stud against the base plate use the level on the inside of the stud to find the point that it is precisely vertical and mark this spot. The floor and the bottom of the floor joist need to be marked so you can frame the wall.

Once you have made sure the wall is plumb you can nail the base plate down with either 3” concrete nails or a nail gun. Place 3” blocks on the base plate to hold up the walls while you install them, these are temporary so do not nail them down.

You have the measurements for the walls so you can put together the frames without having them in place. Pre build the walls and then lift them into place. You can screw the top plate to the floor joists. L-brackets can be used to suspend the floating walls. This will help to distribute the weight of the walls.

The last step is to attach the walls to the bottom plate. You need to allow movement so you are going to drill every 36” on center and place a 60d nail in each hole and nail into the base plate. Once these are in place you need to remove the temporary blocks.

To cover the open area at the bottom of the frame, do not use drywall. Instead use a piece of molding nailed to the side of the base plate. The drywall should only reach the bottom of the wall frame and not beyond. This area must be left open to allow for the movement during expansion and shrinkage.

One final note, you may need to take into consideration the current moisture content in the soil. If it is dry season the walls will most likely raise and if the moisture content is high then the walls will most likely sink from the current position. You may need to adjust the space below the wall to reflect this.