Factory-built housing appears to be getting an even bigger share of the market, the National Association of Home Builders says.

A recent study by Freedonia Group Inc. of Cleveland, OH shows that factory- or systems-built housing will grow 1.2 percent annually through 2005.

Systems-built housing, accounting for 100,000 new homes each year, is constructed in whole or in part in climate-controlled factories and complies with the same building codes as site-built housing.

Because the construction process occurs in a factory setting, it is not subject to the weather and other issues that can affect more traditional construction - known as "stick-built," because it involves on-site framing with 2-by-4s, 2-by-6s, 2-by-10s, and the like.

Factory-built houses include manufactured homes and modular homes. Modular homes also are built in a factory, but in modules or segments, then are transported to a building site where they are assembled into houses.

Manufactured houses, built to requirements established by the U.S. Department of Housing and Urban Development, are usually ready to live in before they arrive on site, while modular homes are not.

About 40 percent of all houses nationwide are constructed in whole or in part using factory-built components, which can save time and reduce waste. And that means lower construction costs, with savings passed on to buyers.

Building components in a factory reduces the need for a large supply of on-site labor, which also lowers construction costs. Many builders believe that factory-produced components reduce on-site costs up to 15 percent during the initial stages of construction.

In a wood-framing competition at a National Association of Home- builders' convention in the late 1990s, it took 148 man-hours to assemble a component-framed structure, compared with 401 man-hours to frame the same house using conventional methods.

The component-framed house also used 5,300 fewer board feet of lumber, and generated 13 yards less of scrap wood than the conventionally framed home.

The savings: about $5,000 in labor and $1,800 in lumber.

In stick-built construction, everything has to wait while the foundation is being dug and poured. A modular house is built in four to six weeks, while the foundation work is completed.

Once the modular house arrives at the site, it goes up inside of a day, is closed up in another day, and then is finished in four to eight weeks.

By comparison, it takes a minimum of six months for a stick-built house. There are a lot of conditions that determine the length of time for delivery - the weather is an obvious one, but if there is a construction backlog, that, too, can cause serious delays.

In modular construction, three-dimensional modules are about 95 percent complete when shipped to a building site. Two or more sections, 12 to 14 feet wide and up to 60 feet long, are combined to create the finished building.

So labor costs for a modular house are limited to an electrician, a plumber, and a carpenter to touch up the drywall and paint.

Panelized housing components are capturing a larger share of the market, according to a study by the Structural Insulation Panel Association of Gig Harbor, Wash.

Between 2000 and 2001, production of structural insulation panel increased from 30 million linear feet to 35 million linear feet.

The wall panels run 8 feet high and 4 to 40 feet long. The panels are assembled immediately after delivery to the site, and a roof can be added to complete the exterior in a few days. Open-wall panels are wall sections containing exterior sheathing only, with plumbing, wiring, insulation, and interior sheathing installed on site.

Log houses and geodesic domes also are factory-built houses, but they are not modular homes. They come in small pieces, like panels and logs.

Recent studies have confirmed an industry-wide belief that log homes are more popular as primary than secondary residences.

The log-home industry is capturing 7 percent of the custom-home market nationwide, according to the Log Home Living Institute. In North America in 2001, the industry created 25,177 structures on a volume of $1.4 billion - an increase of 12 percent in unit production and 46 percent in dollar volume compared with six years ago.

Log-home companies may produce factory-made or hand-crafted houses with solid log walls, 6 to 15 inches thick. The logs must be certified for structural soundness.

The dome, or partial sphere, is a geometric form that encloses the greatest amount of volume with the least amount of surface area. The structure uses triangles as space frames. Geodesic domes are generally installed on a riser wall or base wall over any properly designed foundation type.

Geodesic-dome houses are highly energy efficient and qualify for energy-efficient mortgages.