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By George Porter
A Manufactured Home is a more complicated piece of engineering
than most other homes. Our building code makes us have a multi-purpose
chassis. Strangely, we don't move all that much after the first
installation, but HUD said many years ago that we must have a
frame (transportation system) and I guess that is how the game
will be played. It limits our natural evolution from trailer to
house but those are the rules and I guess we are stuck with them.
There are some advantages to this frame however and if we could
just make the public (and a few salesmen and zoning officials)
understand that, then we would be a lot better off.
Let's make a list of the good things the frame gives us:
1. Mobility. If you ever have to move the home again it is
all pretty much right there waiting to go. Mods are a little more
complicated and stick build is a very big deal.
2. It unitizes the structure. One time I saw a home with a
trussed floor, lots of metal plates on little pieces of lumber,
it had had a rough trip from somewhere and the little plates were
all backing off from the wood and it made the whole floor system
weak. There are still some floors like that today, but most homes
in our industry use big lumber lagged to steel frames. It is so
well connected together that in almost all wind zone 1 homes,
if you secure the frame, you have secured the whole home.
3. You will not find a better system in an earthquake than
a big heavy steel frame. I would prefer to go through an earthquake
in a modern manufactured home with a proper foundation rather
than any other kind of housing structure. The chances of survival
are excellent. In Japan it is a "feature-benefit" used
in the sales process.
4. We save on lumber in the floor. By backing up the floor
joists with I-beams we can use smaller joists and lose no strength
in the floor load.
5. It provides us with the ability to have a shallow frost
protected foundation. The major supports of our homes are tucked
under the perimeter by several feet. When the home has a perimeter
enclosure, such as vinyl with an expansion top cap, then the depth
of the footings can be far less than a conventional foundation
which is located on the outer edges of the home. The area under
the home is protected from wind chill, water, and is a geothermal
zone warmed by the enclosed earth to help retard freezing. Unfortunately
some local authorities are having trouble understanding this and
it cost us lots of extra money for their footings. Maybe, if we
could get them to just crawl under there sometime in the winter
they could figure it out?
6. Steel is lighter than wood of the same strength. In fact
steel is 30% lighter than wood for the same strength.
7. Steel bends. This doesn't sound like a plus but it is. We
can easily camber (bend) steel to sort of build a spring in it.
In fact we have to when we build the home; if we didn't the tail
and belly of the house might drag on the road in extreme cases.
At a minimum it would allow the box to bend so much that it would
cause damage to the home. Manufactured Homes have a frame that
is tailored to fit each home, not only for the length and width,
but for the weight it must carry as well. Modular homes are shipped
on generic carriers and while they do get the job done without
much trouble in most cases, they are not especially engineered
for each home they are carrying. Many times I have seen a lot
of frame sticking out from under a mod where the box is smaller
than the frame by 10 feet or more. Both work, but the Manufactured
Home frame, properly cambered and sized, is a better tool for
8. Steel doesn't absorb moisture. Dampness will not make a
steel beam warp or get soft. Please be aware however, that a steel
beam exposed to lots of dampness over an extended period time
will rust, even if it is properly coated at the start. This is
one of the reasons why site preparation is so important. While
the condition is to be avoided, sometimes in the course of transportation
and or onsite problems such as water heater failure, temporary
extreme climate conditions, or even a broken pipe, the steel will
help hold the floor straight. There is certainly a limit to this,
but a pure wood floor would not survive as well as one backed
up by a steel frame.
9. Steel is an excellent building material. People look under
our homes and think, "Oh my Goodness, this thing is a "trailer,"
it has a steel frame. We have got to stop hiding from this "Trailer
Frame" thing. Sooner or later somebody has to reply to this
strange complaint with the words like, "So what? "or
better yet, "Yeah, isn't it great!" There are some good
things about it and besides that, try and go live in something
without steel, and I don't mean just the nails, bolts and screws.
For years when stick builders need to have a big span or a special
load bearing wall, they always use a steel beam. Every large hotel
or government building in the world uses steel framing. When you
reinforce concrete what do you use? When you want to stick build
a home in a severe wind zone what do builders have use to hold
the rafters to the walls and the walls to the foundation? What
is the Golden Gate Bridge and all the ships in the Navy made of?
Steel of course, so why would we feel we have to be ashamed of
our frame? We probably ought to brag about it!
10. Hey, Leonardo de Vinci's "Mona Lisa" has had
a frame since 1506 and she has been smiling for 500 years! So
how bad can it be?