DIYbanter - View Single Post - Sagging Floors, Jack Posts, Sandwich Beams

(MS) wrote in message ...
I am using adjustable jack posts to level some sagging in my house - a
21' x 26' Cape. The greatest amount of sagging is about 1 ¾" to 2".
The house sags in three distinct areas:

1) Toward the center, along the center beam (originally on three
lally columns)
2) Around the stairs (north side of the center beam [NCB])
3) Along the wall bisecting the house, roughly in half, and
providing (south of the center beam [SCB]) the entry to the kitchen

Gradual extension of the jack post screws (placed under the center
beam and additional plates along various strategic points, SCB, shows
good results with about 3/8" to ½" already regained. This is where the
inexcusable under-design (1947 construction) of the house becomes
evident. The wall which bisects the house north-south and provides the
entry into the kitchen does not rest on a joist. It is instead placed
right smack in the middle, between two joists (7" joists, placed 16"
OC). This wall happens to carry the load for the finished second floor
and is supported by ¾" subfloring only!!!

As the center beam and the joists are beginning to move back into
proper level, the boards under the kitchen entryway wall are beginning
to bow even more. I need to add that this particular area was already
sunk lower than the rest of the house, for obvious reasons. The house
contained a sag within the sag as the main floor came down due to the
settlement of the lally columns, and the kitchen entryway wall itself
then also sagged somewhat (1/2") below the floor level, more or less.

To fix this condition, I plan to add a span of a 5" x 7" beam running
between the joists and directly under the offending wall. Two jack
posts will be placed under the added beam, ensuring that I am raising
the wall in question, along with the rest of the structure.

Once the add-on beam is in place and the leveling is complete, I plan
on adding perpendicular 2"x10" plates securing the add-on beam to both
adjoining existing joists. The permanent supporting new lally columns,
on concrete footings, will go under the new perpendicular plates,
distributing the load along three members.

If you are still reading, here are my questions:

Can I fabricate the 5"x7" beam by combining ¾" plywood with 2x7"
boards? I've heard of this done and it seems to make sense, but I am
not sure if this is a better method than a solid beam. I can see both
sides of the argument: a solid beam can deform in unison due to
internal flaws, etc. OTOH it is a solid piece(!) while a composite
might offer more rigidity, if done correctly, but more components are
involved.

As far as composite beams go - what is the correct method of producing
them? Liquid nails, fasteners, wood glue, clamps?

Anyway, I would appreciate any comments and suggestions you can make.
I am not a professional builder, by trade - as you can tell - and my
methods and ideas might be completely off the mark with the above. If
you tell me I am nuts, I won't take it the wrong way. Thank you for
bearing with it [NPI]!

Michael

I pretty much followed you. Not sure on one point but it is a biggie.
Do not continue jacking on your existing set-up -until- you have
installed the new beam and brought that portion up to the same level
as the othe ones. You are dangerously close to having the center wall
punch right through the floor.

As to your question about the beam. A laminated beam 2x8 with ply
sandwiched between will be stronger than a 1 piece and far more likely
to be straight than one solid wood beam. My method is either
resorcinol glue or liquid nails. The glue probably gives a better
bond. Simple nailing is sufficient, you don't need to clamp it. When
assembling sight down the 2x and place the crowns opposite each other
then begin nailing from one end drawing the loose ends into line. The
closer you get to the end, the harder it will be to draw the ends in
line. This is where you might need clamps. If so, leavit it/them in
place until the glue dries. This results in a straight beam if the
bow in the 2x's are approximately equal. You will need to be careful
in that respect when selecting the lumber.

Harry K