It is hard to know where modular housing ends and prefab building begins. Probably they, as well as the manufactured homes and the building kits we discussed earlier, can all be placed on a continuum we can call "factory assisted" housing. In some cases the factory just assists more than in others.

What is usually thought of as a modular house is two or more three-sided structures that are shrink-wrapped at the factory and shipped by truck or train to the building site where each is lifted by crane on to a prepared foundation then joined together. The modules are usually shipped with windows, doors, cabinets, electrical, plumbing and HVAC systems in place and take very little time to finish on site. Some modular homes look, from the outside, very much like manufactured housing except for the foundation that links them to the land and enables them to be deeded with the land. However, modular building has advanced to a state that enables the building of elegant two (or more) story homes in virtually any architectural style and with interesting design features that make them indistinguishable from their stick-built neighbors.

Hard construction prices have been difficult to come by, which is understandable when one considers the many variables such as finish quality, shipping, and customization that go into a project. One modular manufacturer, however, has provided a little guidance with price estimates for a 1,600 square foot home, exclusive of land. Many of the site-related numbers below can be used to arrive at rough estimates for other types of factory assisted construction.

Modular home, including shipping $ 89,000
Garage (also modular)   20,000
Permits   15,000
Utility connections (if close to site)   8,000
Site prep & foundation   15,000
Set up on foundation   17,000
Engineering and survey (if needed)   3,500
Total $ 167,500

This is about $104 per square foot but does not include any finish work or landscaping and is going to vary according to location. Generally, estimates vary on the overall cost savings from modular construction. Estimates are out there that range from 10 percent to 50 percent.

Other types of prefabs need a good deal more work at the site than modulars.

If you watched volunteers assemble 67 homes for shipping to the Gulf on the Today Show this past week you have seen a form of panelized home construction. The frames of the homes were assembled by hundreds of volunteers then taken apart (probably into four separate walls although that detail wasn't mentioned) and shipped to Louisiana where other Habitat for Humanity volunteers will assemble and finish the homes. On-site finish work was estimated at 30 days per house, but this work is being down with sometimes inexperienced workers.

The Today Show houses are an example of open panels. When factory-built, open panels usually have plywood cladding on the exterior of the frame but interior studs are exposed. Insulation, wires and pipes, and wallboard are installed on site. With closed-panel construction, each panel is finished and inspected at the factory with insulation, pipes, and wiring enclosed behind the interior drywall.

Many stick built homes are actually partially panelized. Roof trusses and floor trusses are increasingly built in factories in controlled environments and checked for compliance with building codes and blueprints then shipped to the site.

Panels, once at the site, are typically assembled by local construction crews, however, some manufacturers ship their product complete with an experienced crew which does the assembly work on site.

One manufacturer of building panels estimates that the units can cut the process of closing the home to weather from 10 to 14 days to 2 to 4 days, at which point weather, normal weather at least, ceases to be a construction factor.

Wooden studs are not the only materials used in panelized home construction. Lightweight steel or concrete are also used in the place of much of the wood. In one interesting variation expanded polystyrene panels can be snapped together to create walls of any thickness in 2 to 4 inch increments. Space between the panels is then pumped full of concrete which hardens into a strong monolithic core. Any exterior or interior finish can then be applied. The polystyrene panels can be cut to allow for arches or other architectural details. According to the manufacturer this construction method provides significant energy savings, noise reduction and a four hour fire rating. The construction method can be used to build to any seismic or hurricane standard and won't support growth of mold or mildew.

There are other processes and materials in use and an Internet search on prefab, panelized construction, and concrete home construction will keep you busy for days.

Any of these alternatives to totally site built construction offer the benefit of factory conditions mentioned earlier – greater adherence to standards, computer-assisted construction, freedom from weather delays, and the greater buying power of a mass-market purchasing. One manufacturer pointed out a cost benefit that we hadn't thought about. Back in 1996 the National Association of Home Builders estimated that a 2,000 square foot home results in 8000 pounds of "waste" that ends up in dumpsters and eventually in landfills. At that time builders were paying an average of $511 for disposal not to mention the labor costs involved in policing the site. Panelized construction supposedly virtually eliminates waste on the site and material waste is also reduced because the manufacturer pre-determines the most efficient use of materials when designing the panels.

Prefabs and modulars have long been an accepted form of building in Europe and some of the most exciting new concepts are heading here from European builders and designers. IKEA, the innovative Swedish design company, is now doing homes in boxes for large scale developments in Scotland and other areas. Imagine the day when you can pull up your Penske truck at the IKEA loading dock in Atlanta or Elizabeth, New Jersey and load it up with not only tea candles, a couple of wastebaskets, and the furniture you need for the living room, but the whole new house, assembly instructions included.