Most house built since the 1920s have wood-frame construction: a system of wooden wall studs, floor joists and other wooden members that provide structure and a framework for attaching finished surfaces.
The high cost of lumber is fueling an interest in steel and other alternatives, but wood is still-far and away-the most popular framing material. In most cases, even houses that appear to have brick or stone walls actually have wood frame construction beneath their masonry façade.
There are two basic framing methods: platform and balloon construction, as shown at right. Platform construction is much more common than balloon framing, though balloon framing was employed in many two-story houses before 1930.
With both methods wall studs and ceiling and floor joists occur every 16 or 24 inches, measured from center to center. These standardized layouts take advantage of floor, ceiling and wall materials with the least cutting and waste. Most older houses have 2 by 4 wall studs spaced 16 inches on center; many newer houses have 2 by 6 wall studs either 16 or 24 inches on center to make exterior walls stronger and allow a larger cavity for wall insulation.
Exterior wall sheathing adds rigidity to the structure and provides a flat base for siding, stucco or other exterior wall finish. Older homes have diagonal sheathing-1/2 inch-thick boards nailed on the diagonal. Most newer homes have plywood or similar composite panel sheathing.
Exterior roof sheathing serves the same purposes for roofing. Most contemporary roof sheathing is either plywood or oriented-strand board (OSB) panels; spaced wood sheathing is common for wood shingle roofs.
With platform construction, walls sit on top of subflooring. Multi-story houses are built one level at a time-each floor provides a platform for building the next series of walls. Nearly all contemporary houses are built using the platform construction method.
--Don Vandervort
