How to Add Basement Walls to an Existing Basement

Lay out the location of the new walls by drawing their outlines on the floor with a magic marker or a pencil. This step isn't necessary for perimeter walls, which will be set against the exterior walls. For other walls, mark both sides of the intended wall so you don't accidentally build a wall on the wrong side of your line.

Install the bottom plates for the walls using the lines you drew as a guide. The bottom plate is the horizontal 2-inch-by-4-inch board at the bottom of the wall, on top of which all the studs sit. Attach the plates to the floor with a powder-actuated nail gun or with a hammer drill and 3-inch concrete screws. While most walls are built on the floor and then put into place, it's easier in a basement to build the walls in place because of space constraints.

Determine the location of your top plates by hanging a plumb bob from the ceiling and adjusting it until its point is touching the edge of the bottom plate, then repeat on the other edge. Mark where the string is on the ceiling for each edge. These marks represent the location of each side of your top plate.

Attach the top plates to the ceiling by driving 3-inch wood screws through the top plates and into the underside of the floor joists.

Measure the vertical distance between the top and bottom plates, and cut your studs to this length. If your basement is uneven, you may have to cut each stud to a custom length.

Install the studs on 16-inch centers to accommodate insulation. Be sure the studs are vertical by checking them with a 4-foot level.

Install any needed electrical receptacles and switches by drilling holes through the studs and running wires from the main service panel of the house to the locations of the outlets.

Screw the outlet boxes to the studs in the desired locations and run the wire out the front of the boxes.

Install insulation in any perimeter walls. Install sound insulation in rooms where you might create a lot of noise, such as a home shop.

Measure the locations of outlets and light switches. Transfer these locations to a piece of drywall and cut out holes that are 1/32-inch larger than the electrical box sizes. Trim the pieces of drywall to fit by cutting them to the height of the wall.

Attach the drywall to the studs using 1 1/4-inch drywall screws. Place the screws at 12-inch intervals along the length of the studs.

Apply drywall mud and drywall tape to the joints between the sheets of drywall and to the holes made by the screws. Allow the mud to dry overnight.

Sand the mud smooth with sandpaper and a sanding block, and apply another coat if necessary.

Apply primer to the entire wall surface after the mud has been sanded perfectly smooth. Allow the primer to dry overnight.

Apply a coat of finish paint to the wall.