Modular Homes and Prefab Housing Can Save Time and Money
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.