Floor and Ceiling Framing

Though some floors are built on a concrete slab-flat on the ground-most floors are raised above the ground. Raised floors are more resilient under foot and provide access for heating equipment, insulation, plumbing, wiring and other mechanical equipment.

A raised floor is constructed with a wooden framework that bridges from one exterior wall to another. This framework may or may not be supported intermediately by girders, beams or walls. On upper levels of a house, the underside of the floor framing generally serves to back ceiling materials. Ceilings are usually built just like floors, only they may be constructed of lighter materials because they're not intended to carry the same loads.

A floor's framework is made up mostly of wooden joists that run parallel to one another at regular intervals. Floor joists are typically 2 by 8s, 2 by 10s or 2 by 12s; ceiling joists are usually smaller-2 by 6s or even 2 by 4s in older homes. Some newer homes have manufactured, I-beam shaped joists.

Floor joists, spaced on regular intervals, span the areas between supports such as walls, foundations, girders and beams. Normal spacing is 16 inches "on center" (from center to center), though some floors may have joists on 12-inch or 24-inch centers. Joist sizing and spacing are determined by building codes, which are based on engineering requirements.

Joist headers run perpendicular to joists, capping their ends.

At foundation level, floor joists rest directly on a sill that is treated with preservative so contact with the foundation will not encourage termites or rot. Exact construction and connection with wall studs depends upon the method of framing.

Subflooring provides a base for finish flooring and also serves as a platform during construction. It may be made of boards laid either at right angles or diagonally across joists. Or the subfloor may be made of plywood or other panel products that are laid perpendicular to joists.

Solid blocking or metal bridging prevents joists from twisting and helps distribute loads evenly.

Joists are spliced over beams or other supports. They may be butted end-to-end and connected with plywood gusset plates or lapped.

MORE ABOUT:
/ Load-bearing walls / / Foundations / / Foundation footings / / Standard wood framing /
/ Balloon framing / / Wall framing 1 / / Wall framing 2 / / Floor & ceiling framing /
/ Roof framing 1 / / Roof framing 2 /

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