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I Think There's A Problem Here
By George Porter
Did you ever have one of those little thoughts nagging around
in the back of your mind while you're doing something that you've
probably done a hundred times before? It's the little notion that
you think there's something wrong here, but you just can't quite
put your finger on it.
Well, that little thought boiled to the surface the other day
when I was reviewing an installation manual for a manufacturer.
I was doing the part where they described mating up one half of
a double to the other and most of the companies treat this in
pretty much the same fashion. They say you block and level one
half of the home, the heavy half if you have a choice, and if
the manual hasn't been looked at by anybody in the last ten years
or so, it probably says you go get some greased boards and slide
the house over. (At this point, I generally mention something
about rolling and jacking equipment.) But, nevertheless, it basically
says you get one half over there and then you raise the inside
I-beam until the two floors are joined together and there is a
gap in the roof. Most manuals then say you then lag-bolt the two
halves together loosely, then you raise the outside I-beam until
the floor and the raised half becomes level with the floor in
the half that you had previously set.
Now here's the problem, what happens to the house between the
outside I-beam and the marriage wall? If the floor remains straight
across, then the inside I-beam will have to lift off of the inside
blocks. But with all that weight, it can't. So it does one of
two things. The home either sags a little to leave the I-beam
sitting on the blocks and putting large force on the marriage
wall, or the lag-bolts will rip out. If you don't think you're
inducing some kind of stress into the home by doing this, next
time try it just once without putting the lag-bolts in. The floor
in the half you're jacking will drop below the floor of the one
you have set when you raise the outside I-beam. So, if it stays
put when you do this, and if you've put enough lag-bolts in it,
it should, then the floor joists and decking and frame and outriggers
on both halves of the home are put under a considerable strain.
If you're still using a carpenter's level, instead of a water
level, to set all the piers first, you'll probably never discover
this strain and it will be trying to relieve itself over the life
of the home.
As these floor joists and decking relax, creaks and separations
will occur along the marriage line and in the floor of the home.
Drywall may develop stress cracks and you'll need to make a couple
of more service calls on this house because of "settling."
If you set all the piers under all four I-beams with a water
level, raise the home, bring it over and set it down on those
piers, the home should be extremely tight together, the floor
should be level, and when you bolt those two halves together,
there should be very little strain between them and the structure
will not be trying to slightly change its shape as time goes on.
Think about this next time you're putting a double together.
I think maybe you'll come to the same conclusion.