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Floor Has A Hump
Dear HammerZone,
I'm remodeling my kitchen and family room. I'm replacing the carpeting
with laminated flooring.
When I took the furniture out of the family room, and pulled up the
carpeting and pad, I discovered I had a "hump" running across
the room, in the same direction as the joists under the sub-floor.
Measuring with a 4 ft level, I narrowed the problem down to a single joist
(approx 12 ft long) that appeared to be bowed upwards almost 1" in
the middle.
When the room was carpeted, that kind of hump didn't make much difference,
since it was fairly near the end of the room. But I really think it will
be noticeable when I put down the laminated floor.
What would you do?
I loved your dissertation on "jacking up" a floor ... can I
"jack down" this joist?
Thanks for your help!
T. R. Berta
I
was in a shoe store recently and I saw the solution to your problem.
That is really weird because it was two weeks before you asked
your question.
Seriously. I was in Rockford Michigan, near Grand Rapids, at an outlet
store for Wolverine World Wide, which makes numerous brands of shoes and
boots such as Hush Puppies. While my girlfriend browsed for shoes, I
stood around and my mind wandered to more interesting things such as the
structure of the building. The store is housed in an old factory, dating
back to perhaps the late 1800's.
And I was a little surprised to see that all of the floor joists above
were "discontinuous", that is, they had been spliced in the
middle of the span.
The joists in question were huge, about 4x12, which was typical for
factory buildings of that era. And the joists spanned about 20 feet from
one wall to a beam in the center of the room, and kept going for another
10 feet. The remaining 10 feet of span was accomplished with ANOTHER
piece of 4x12.
This type of construction is not very common, but it can be done. They
had joined the two sections of joist with 2x10 "scabs" about 4
feet long, on each side of the joist. The scabs were clamped together
with four large bolts and washers, which is the key to making these
splices work.
It was weird though, seeing a whole row of joists that were spliced
together. I've seen a few odd splices done for repairs, but this
structure must have been built this way.
If I was faced with a problem of a joist bowing upwards, my approach
would be to "Slice and Splice".
1. I would first verify the amount and location of maximum bow. I
would use a length of string to create a perfectly straight reference
line next to the top of the joist. I would secure one end of the string
to the underside of the floor, just a fraction of an inch from the
joist. The other end must he pulled very tight and held or secured to
the floor. Then I would be able to measure the exact amount of error and
the location of the worst deviation. It might be necessary to remove
blocking or bridging to create a clear work area.
2. I would cut right through the joist, severing it into two
pieces. The joist could be replaced with two sections of new wood, but
that is a lot of hassle. My approach would be to let the cut joist sag a
bit (I might prop the ends up from below with 2x4's) until the floor
above is flat and level.
3. Then I would splice the joist with an 8 foot long piece of
lumber (the same size as the original joist) on EACH SIDE of the joist.
The key to success is using the right fasteners. First I would nail the
splices in place with a dozen (or more) 16d nails. Then I would install
at least 3 large bolts on EACH SIDE of the splice, to clamp the wood
tightly. These bolts should be at least 5/16" diameter (and
whatever length that will leave some thread sticking out at the end,
perhaps 5 or 6 inches long) and they also need to have very large
diameter washers (such as washers for 3/4" bolts) under the bolt
and nut to prevent crushing of the wood fibers. There also needs to be a
lock washer under the nut.
This
article shows what I mean about washer size.
Some Relevant Photos:
| These
connectors are actually pieces of 3/8" threaded rod.
These are joining floor joists together, but the connection is
supported by a lally column because there is not enough wood
available for adequate overlap. |
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| This
closer view shows the washers... a large flat washer, a 3/8"
flat washer, and a lock washer. |
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The Opposite: Raising A Joist
| I
installed this bracing in the attic to support a ceiling joist
that had sagged. The vertical post on the right is the location of
the sag, the rest of the wood is just to provide additional
stiffening.
To raise the joist I simply made
a "T"-shaped post from an 8-foot 2x4 and a scrap of
wood, and placed it under the joist. |
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The trick is to make a post a fraction
of an inch longer than the proper ceiling height. Then the ceiling can
be raised slightly by hammering the post more towards vertical, and
lowered by making the post less vertical.
I suppose this type of apparatus could
be used to pull a joist downward.
Bruce W. Maki, Editor.
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