Basement framing is not much different than the framework on the upper floors. The frame must be adapted to the concrete surface of the foundation and be built to accommodate the various obstructions such as columns or mechanical equipment, and protrusions, such as ducts or utility lines, which found in an average basement.
The finished interior space typically has less than the standard 8-foot ceiling height and may contain seemingly random jogs, soffits, and projections. Before any work begins in the basement, the must be sufficiently sealed so that no moisture is seeping through the foundation walls and no water is collecting on the floor. Any wall assembly that contains excessive moisture within its cavity will soon have to be replaced.
Begin by erecting the exterior stud walls along the basement perimeter. If batt insulation will be installed, create cavity space by using 2x-4-inch wood studs. Otherwise, 2x2-inch furring spaced 16-inches apart on center can be nailed and glued directly to the foundation wall. Using pressure-treated 2x4-inch lumber, cut the bottom plates to length and secure them to the concrete slab using adhesive and concrete nails with 3-foot spacings.
Install the top plates by nailing them to the bottom edges of the exposed floor joists. If the joists are perpendicular to the top plates, nail through each joist where it intersects with the plate. If the joists are parallel to the plates, install blocking flush with the bottom of the joists at 3-feet on center.
Use a level to determine whether the plates are aligned properly and that the wall is plumb. Install the studs one at a time at 16-inches on center by toe-nailing into the top and bottom plates. Frame the rough openings for any basement windows and doors. Maintain access to junction boxes, meters, cleanouts and valves by framing out openings where needed.
Interior partition walls are framed in much the same way. Using a chalk line, layout the wall plan on the slab and install the bottom plates. Plumb and snap chalk lines along the bottom of the joists to show the locations for the top plates. If the concrete slab is found to be uneven in some places, you may have to trim the length of individual studs.
A soffit is constructed like a miniature stud wall (2x2-inch lumber can also be used), hung from the bottom of the joists and built wide enough and low enough to clear the protrusion by an inch. Nail a 2x4-inch nailer against the stud wall adjacent to the soffit and level with the soffit’s “bottom plate.”
Blocking is installed between the “bottom plate” and the nailer, effectively building a box around the protrusion. Soffits are installed plumb and level. They should occupy minimal space. Large beams can simply be concealed with a layer of sheetrock. Free-standing steel lally columns can either be left exposed or boxed out and trimmed with a finishing material.