Raising
a house, or just a part of a house, is serious stuff. It may be
within the grasp of a serious do-it-yourselfer, IF the proper
precautions are taken. I’m not going to actually recommend that
you tackle this project, that is something only you can decide. I
have known people who would ask contractors for quotes… with the
intention of only picking their brains for ideas. That is
considered impolite in this business, so I can’t recommend it
either.
But if you do try this, then the
following may help.
The Short Answer:
Raising a part of a house by 2
inches is not excessive (in my opinion). And you could do the
entire lifting process is 10 minutes… though there would be
negative consequences, primarily cracked plaster. When I was
taking Building Construction Technology courses in college I heard
a general rule about leveling houses: 1/8 inch per day maximum
to prevent excessive cracks in drywall or plaster. So you could do
your lifting job over a two week span to be safe. But because of
the large amount of settling there is a high likelihood that you
will have some cracked plaster or bulged plaster.
The Long Answer:
Houses typically don’t weigh as
much as people imagine, especially when they are built with common
building materials. By that I mean conventional wood framing,
asphalt roof shingles, and materials that are NOT stone, concrete
or masonry. For instance, one of our project houses has concrete
block walls on an absurdly shallow crawl space. We would raise up
the house and excavate a proper basement, but lifting a house with
concrete block walls would be impractical.
My first opportunity to raise
part of a house occurred when I needed to lift up the middle of a
"built-up" beam in a basement, because it had sagged in
the middle. I used a 6 Ton hydraulic jack with a 4x4 wood post for
jacking, and then I supported the beam in the middle with a new
adjustable steel lally column. It all went smoothly.
When lifting a building one needs
a thorough understanding of the structure and which walls are load
bearing. But first one needs to understand house framing and be
able to identify the parts of the structure. I would guess that a
40 year old house would be built with "platform"
framing. I recommend that you do a little reading about house
framing methods. There is also "balloon" framing and
"post-and-beam" framing, both of which are quite rare
for houses built after WW2.
I would also want to know why the
house settled in the first place. It is quite possible that the
original builders failed to compact some soil and the foundation
settled soon after construction. If so, then there should not be
any more settling. But if your house is built on a "problem
soil" such as muck or decaying organic matter, then the
problem could continue. I would bet that you will see no further
settling, but you should monitor the situation. In either case,
then you should be able to see cracks in the foundation that are
consistent with the settling. That is, you should be able to find
some cracks in the foundation wall that are tapered (larger at the
top). Perhaps you can locate a pair of similar sized cracks that
seem to delineate the settled portion of the house.
You must also disconnect the
house from the foundation, if it's attached. Today most houses are
anchored to the foundation with anchor bolts or anchor straps. The
straps are just nailed to the mudsill. Anchor bolts use large nuts
and washers to clamp the mudsill to the foundation. You may be
able to locate these nuts in the space between the joist ends. But
I have seen houses built as recently as 1975 (in Wisconsin) with
no mudsills and no anchoring.
Lifting a house involves
understanding some things about allowable bearing pressures.
Wood can tolerate only about 625 pounds per square inch (PSI) of
compression load. Concrete can handle 3,000 PSI, and steel can
handle easily 30,000 PSI. These figures illustrate why it is so
easy to punch a hole right through a floor or into joist when
attempting to raise a house.
What I’m saying is: the lifting
force must be spread out considerably. And, the wood structure
immediately above the lifting device must be monitored for
crushing of the wood fibers. Crushing of wood fibers MUST be
avoided.
It is also possible to punch a
hole through a concrete basement floor with a hydraulic bottle
jack or a lally column. I have always used one of several heavy
steel plates under the hydraulic jack. I have a couple of pieces
of ¼ inch steel plate that I use under the jack, between the jack
and the lifting column, and between the lifting column and the
wood structure. I have also managed to bend these plates. I would
recommend nothing less than ¼" steel plates for distributing
loads. The ones I have are about 4" x 6", but you can
use smaller plates, possibly as small as 3" x 3". You
might try calling some smaller metal fabrication shops, they
probably have scraps that they can sell you, or they can quickly
cut some steel for you.
But BE CAREFUL with these.
The biggest risk I have seen while raising houses has been the
danger of a heavy steel plate falling from the top of the lifting
post while I am crouched down fiddling with the jack. It takes
only 600 inch-pounds of kinetic energy to deliver a fatal skull
fracture. So a 10 pound object falling from 60 inches above could
kill someone. This really is a "hard-hat" type of
project.
Let’s do some engineering here:
Take a 3.5" wide wood beam (i.e. 4x6 or 4x8) with a 3"
wide by 4" long steel plate at the top of a column. There
would be 12 square inches of bearing area. Each square inch can
tolerate about 625 pounds of force. That amounts to 7,500 pounds
that you can safely lift using such a plate to spread the load.
(The goal here is to get as much
bearing area as possible while keeping the steel plate weight to a
minimum… to reduce the risk of a falling object. You could also
drill two small holes in each plate so you can screw them securely
in place on the bottom of the big wood beam.)
I’d bet that the corner of your
house weighs less than that. You didn’t mention the size of the
area that needs raising. Let’s say it was 10’ by 10’. That
would be 100 square feet, but since we are raising a
triangle-shaped area, we are only lifting half of that. Assuming a
dead load of 30 pounds per square foot (standard load for a
bedroom or living room), that would be 1500 pounds to lift. But
that is just the first floor. If there is a second floor, double
that number. And then the roof weight must be added in. I would
guess 20 pounds per square foot would be the design load in your
area. You could use 30 to be safer. That would be another 1500
pounds to add to the total load calculation. So a 10’ by 10’
corner might weigh about 4500 pounds. That’s not much, really. A
6 Ton bottle jack could do the trick, but I’d recommend buying a
12 Ton jack, it won’t cost much more.
Then you need to know just where
to lift. You need to basically replicate the support of the
foundation wall. So you need to lift in a long strip along the
ends of the floor joists, just a few inches inside the
basement wall. And you cannot simply raise one floor joist at a
time. So you’ll need a long beam to support all the joist-ends
that need raising. I would recommend at least a 4x6, but a 4x8
sounds better. You can use a "built-up" beam made from
two or three 2x8’s (or larger) nailed together.
This beam will have to be
supported by a lally column at each end. And you’ll need
a third lally column to put on top of the bottle jack. To hold the
beam close to the joists (while I am re-positioning columns and
such) I have used rafter ties. It can be quite a juggling act to
hold the beam up in the air and also two supporting columns.
Once the beam is in position and
pushed up against the joists with the lally columns, you can use
the jack/column rig to lift each end of the beam a little bit at a
time.
Raising a house can be a lot of
fun, but it might be best to spread the fun out over a few days or
weeks. Besides, the house will appreciate it. Raising a section of
a house by an inch or two will create a tremendous noise as the
wood framing moves and rubs together. These noises can be
nerve-wracking, so do a little at a time. Expect to hear snaps,
crackles, and pops for hours, even days, after each lifting
session. I would also recommend a good helper to hold and tighten
the lally columns while you raise the beam.
When we bought lally columns,
there was a choice of capacities. The lighter-duty column was
rated at "one elephant" and the heavier-duty columns
were rated at "four elephants". We bought several of
each type, but I was most impressed with the "four
elephant" type. They had much heavier steel plates for the
column ends. The light-duty columns had such thin end plates that
they always bent into a cup shape. Also, the heavy-duty columns
never showed a tendency to bow. Columns usually fail by buckling.
This mode of failure will first appear as a slight bowing in the
column. For this reason I strongly recommend that you buy three of
the heaviest-duty columns you can get (within reason… I think
the heavy duty columns we bought were rated around 14,000 pounds
at full height).
Measuring:
You will also need a good-quality
level, at least 4 feet long. I understand that
"box-beam" type of levels are generally the best. You
can get a premium 4 foot Stabila brand of level for about $70.
You’ll be the envy of your neighbors. You can also use a line
level, which slips over a tight string, but those don’t work
well. I have used an electronic water level, but it is a hassle to
use unless I need to locate elevations in different rooms. You
also might consider renting a laser transit level, or even just an
old-fashioned telescope transit level. You’ll only need it once,
before you start the jacking. You can use it to determine the
exact amount of settling, and then to make a mark on the
foundation walls (or some other structure that doesn’t get
raised) from which you can measure up to the floor structure as it
is raised.
Filling:
When all the raising is done, you
will need to install shims (such as strips of pressure treated
plywood) between the mudsill and the foundation. Don’t stick
your fingers in there, if the house falls it’ll really hurt! Use
a prybar to position things. Since you should have a tapered shape
to fill, you will need a variety of thicknesses of plywood or
other hard wood materials. Any wood next to concrete must be
pressure treated or preservative treated, to prevent rot. I would
caulk all the small holes between the filler pieces, to reduce
cold air infiltration and bug infestations. Some people use mortar
to fill this gap, and it may look better from the outside if the
filler area is visible. If you use any cement-based product, it
needs to be packed in tightly, and you really should wait 7 to 28
days to apply load to it.
I usually raise houses a small
amount more than I need to (maybe 1/16 inch), so the shims do not
have to be jammed in so tightly. Besides, the filler material may
compress or settle slightly. And don’t be disappointed if you do
not get the house totally level. The floor joists may have taken a
"set" or permanent curvature over time.
This is a very serious project,
and if you tackle this I recommend that you take your time, and
maybe do some more research (but I don’t know of any articles or
books on raising houses).
Bruce W. Maki, Editor.
