It is hard to know where modular housing
ends and prefab
begins. Probably they, as well as the manufactured homes and
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
|Modular home, including shipping
|Garage (also modular)
|Utility connections (if close to site)
|Site prep & foundation
|Set up on foundation
|Engineering and survey (if needed)
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
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
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
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,
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.