How to Make a Room in a Cellar

Sketch the layout of the cellar onto a piece of paper, marking the locations of items such as the staircase, water heater, furnace and support posts. Moving these items may not be possible, or only at great expense, so working around or incorporating them into the room's design is probably your best option.

Repair cracks in the floor and walls of the cellar. Patch smaller cracks by chipping away at the area surrounding the crack with a hammer and chisel until you reach the concrete underneath the crack, then fill the crack with patching compound. If the cracks are 1-inch-wide or wider, have a contractor inspect them as it could be the sign of a problem with your foundation.

Screw sill plates to the floor with masonry screws in the locations where the walls will stand. These are pressure treated 2-by-4 boards that are resistant to water damage, which helps protect the untreated lumber of the wall framing.

Construct the frames for the walls by cutting untreated 2-by-4 boards that match the length of the sill plates (the top and bottom frames), and nailing wall studs between them. Keep the spacing between the studs no more than 16 inches. Nail the framing to the ceiling joists and the sill plates.

Install the electrical wiring. You can install the wiring and outlets yourself, but local building codes often require that a certified electrician connect the wiring to the main electrical panel, and inspect any work you complete yourself. If you don't have experience installing electrical components, have the electrician do all of the work.

Install the heating, air conditioning and ventilation (HVAC) ducts. If there are ducts adjacent to the area where you're building the room, you might be able to do this yourself, but if you need to run an entirely new line to the room, you may need to hire a contractor. Local building codes may also require that you hire a contractor to complete this work.

Cover the outer edge of the framing that isn't against the foundation walls. Use drywall if you want a more finished look, or sheets of 1/2-inch plywood if you don't care about the room's outer appearance.

Install rolls of fiberglass insulation between the studs. Place the foil or paper-backed edge facing toward you, and staple the edges of the paper to the sides of the studs. Don't compress the insulation because it will lose its effectiveness.

Install the drywall panels to the ceiling joists and wall studs inside the room with drywall screws. Cover the seams between the different panels with joint compound and drywall tape, then sand them smooth after they've dried.

Apply a coat of primer to the drywall and allow it to dry, then paint the room with two coats of paint. Allow the first coat to dry before applying the second coat.