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Old 11-11-2008, 04:47 PM   #1
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Adding support to "springy" floors-this mom's got to do it herself!


Hi!
My kitchen/family room ~12.5 feet wide and 30 feet long, built over a dirt-floor crawlspace that's about 4 feet high. The 2x10 floor joists span the 12.5 foot dimension (I haven't measured the spacing). There is no bracing/blocking between the joists. The floors have been kinda springy since the house was built 14 years ago, but is more noticeable now that we've got full-sized teenagers charging through it!

I'm tired of the kitchen floor moving, and want to add an additional support beam in the crawlspace, mid span under the floor joists. From things I've read elsewhere, this seems like the quickest, easiest, and most effective fix for my situation.

So, I'm looking at a pair of 2x10s running down the 30' direction, supported by 4x4 wood support posts at 8-10 foot interval. What I'm looking for is some details of how to actually do this. How do I join the paired 2x10s (adhesive and nails from what I've read, but how many and what size nails, will I need to clamp the boards until the adhesive cures?). How to span the 30' length (offset where board ends come together, or line them up and make sure they're over the support post? Should I use those hammer-on metal joining plates? Something else?)

What sort of "footing" do the support posts need? (the crawlspace is earth, seems compact at the surface) Do I need any hardware to connect the post to the beam and the beam to the joists, or can I just toenail? something else? How do I get this new beam/posts tight up against the joists so that this effort will actually work?? Any considerations I've overlooked?

Anything you can offer would be most welcome.
-Linda

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Old 11-11-2008, 11:11 PM   #2
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Adding support to "springy" floors-this mom's got to do it herself!


First off you have to determine if the bouncy floor is the joists or the flooring. If it's the flooring your plan will do little to nothing to fix your problem.

The flooring could be substandard by today's standards but was accepted when it was put in.

Once you determine what is really the problem then you can devise a plan and we would be glad to help you out.

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Old 11-12-2008, 09:30 AM   #3
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Adding support to "springy" floors-this mom's got to do it herself!


Ah - didn't think about the actual flooring! I still have the plans/specs floating abound in a file drawer. I'll see what I can find out tonight.
-Linda
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Old 11-12-2008, 02:24 PM   #4
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Adding support to "springy" floors-this mom's got to do it herself!


If the house is only 14 years old, I would expect your floor is fine, and the problem is the span. In my world 12.5' is a bit far for 2X10's, but Marvin's right, it would be best to make sure of the problem before you start fixing.

If you elect to brace the joists, here's what I would do (others will surely disagree, but I'm at the keyboard now):

Start with 10' 2X10's so you can haul them under there. Cut one in half and start with the half on one side of your beam so the joints in the 2x10's don't line up. I'd nail them together along with glue, but I have a nail gun. If you don't, you might consider 3" screws or lags, which could be shot with a drill. I would let the nail/screw/lag hold the boards together 'til the glue sets.

Put up an assembly on one of the full-length and one of the halves first, they can be toe-nailed or bracketed, all you're trying to do is hold up the beam until you get the posts in place. Add full lengths to alternating sides, gluing and nail/screw/lag and you go.

When you're done, attach a brace from the beam up to the floor joists in some fashion to hold the beam perpendicular to the joists when you start applying up-force later.

The 4x4's should work fine as down-supports, and once you get them wedged in, it shouldn't matter much what you use to hold them in place under the beam - the weight should keep them in place.

Many will come on and say to dig and pour concrete footing pads for the down supports, which would be the absolute best approach, no question. However, digging and pouring in a crawlspace is a pain! I'd go to a builder's supply and get a pre-formed concreted post block. They have a pocket in the top that is designed for a 4x4 to stand in, and slots that work well for shims to be hammered in. Place the blocks where you want them, and make sure they are level.

Measure from the bottom of the post-pocket in the block to the bottom of the beam, and cut your posts about an 1/8" shorter so you can hammer them in place (if they're the same length you'll never get them upright). Put the post in the block, and hammer tapered shims under the bottom of the post in the slots in the block to raise the post up tight, then anchor it to the beam (see above). The blocks may settle over time, so make sure you use enough shims to be able to come back under occasionally and hammer them in a bit more.

As I said, this is my advice, there are lots of other ways, which I'm sure will be pointed out.

Good luck - and if any of those teenagers are boys, MAKE THEM HELP YOU! Boys are supposed to help their Moms.
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Old 11-12-2008, 02:39 PM   #5
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Adding support to "springy" floors-this mom's got to do it herself!


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Good luck - and if any of those teenagers are boys, MAKE THEM HELP YOU! Boys are supposed to help their Moms.
Hey, even if they are girls make them get out there and help.

My daughter can hang sheet rock with the best of them. She once got a job because they questioned her mechanical skills. She told them she used to help her dad rebuild engines and can do break jobs and lots of other stuff. She got hired on the spot.
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Old 11-12-2008, 02:48 PM   #6
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Adding support to "springy" floors-this mom's got to do it herself!


Absolutely true Marvin. I only have boys; 14, 15, and 19. I'm continually prodding them to act like men ought to and it drives me nuts to see a woman in need of assistance with able-bodied men just watch!
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Old 11-12-2008, 03:44 PM   #7
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Adding support to "springy" floors-this mom's got to do it herself!


Running a beam full length may be over-kill.

You should have cross bracing in the joist bays! If these are missing, its a simple process to remedy.

Pre-cut cross braces can be had at most building centers.
They are installed diagonally in each bay and inline from bay to bay!
They are usually nailed in place, but I would suggest using screws would be easier to retrofit.

2X10 joists on a 12 foot span should be quite adequate if they are cross braced.

I once built a house that was a story and a half design.
All the 1st and 2nd floor joists were 2X8X12 with cross bracing throughout and I never had a bounce problem.
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Old 11-12-2008, 04:07 PM   #8
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Adding support to "springy" floors-this mom's got to do it herself!


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I once built a house that was a story and a half design.
All the 1st and 2nd floor joists were 2X8X12 with cross bracing throughout and I never had a bounce problem.
This is what made me think she was having a flooring problem.

2x8x12 should be fine for her situation.

Pictures of what is going on in the crawl space would be nice.
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Old 11-12-2008, 08:54 PM   #9
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Adding support to "springy" floors-this mom's got to do it herself!


Marvin - I checked the house plans, and the floor is 5/8 inch T&G, glued and fastened. The kitchen floor is vinyl, the family room is carpet - so there is no flooring of any substance to add additional strength to the floor. The joists are spaced 16" oc - so could the floor decking be the principal problem rather than the joists themselves? How can I tell whether the problem is the joists or the floor?

If it's the floor, it seems that adding one (or two?) rows of solid blocking (as opposed to the cross bracing suggested by wildie) would be the thing to do because the blocks would add addition points of support for the floor deck. That true?

ojay - thanks for the how to on the support beam. If that's what I need to do, you have given me just the sort of info I was looking for! Perfect!

As for pics in the crawlspace, I don't have a digital camera readily available - sorry.

So - how do I figure out what I need to fix?
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Old 11-12-2008, 09:37 PM   #10
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Adding support to "springy" floors-this mom's got to do it herself!


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Originally Posted by LOStouten View Post
Marvin - I checked the house plans, and the floor is 5/8 inch T&G, glued and fastened. The kitchen floor is vinyl, the family room is carpet - so there is no flooring of any substance to add additional strength to the floor. The joists are spaced 16" oc - so could the floor decking be the principal problem rather than the joists themselves? How can I tell whether the problem is the joists or the floor?

If it's the floor, it seems that adding one (or two?) rows of solid blocking (as opposed to the cross bracing suggested by wildie) would be the thing to do because the blocks would add addition points of support for the floor deck. That true?

ojay - thanks for the how to on the support beam. If that's what I need to do, you have given me just the sort of info I was looking for! Perfect!

As for pics in the crawlspace, I don't have a digital camera readily available - sorry.

So - how do I figure out what I need to fix?
I believe, although I'm not a structural engineer, that cross bracing is more effective than solid blocking.
I think it has to do with transfering the weight from being a verticle load to being a horizontal one.
Why this wouldn't happen with blocking I'm unsure!
My hunch is that the load continues to go straight down, whereas the weight on the end of the cross piece is deflected toward the adjacent joist and so on horizontally. Akin to standing domino's that fall in order when the first one is pushed.

To ascertain whether you have a floor or joist problem, go into the crawl space and place one hand upwards into the joist bay and against the floor. Place your other hand on the bottom of the joist.
Then have someone walk over-head and see if you feel any difference in the deflection.
Do this in several locations, to get an idea of what the over-all situation is.
Another option would be to simply use a tape measure from the floor and observe how the gap changes when someone walks above.
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Old 11-12-2008, 09:38 PM   #11
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Adding support to "springy" floors-this mom's got to do it herself!


Quote:
Originally Posted by LOStouten View Post
Marvin - I checked the house plans, and the floor is 5/8 inch T&G, glued and fastened. The kitchen floor is vinyl, the family room is carpet - so there is no flooring of any substance to add additional strength to the floor. The joists are spaced 16" oc - so could the floor decking be the principal problem rather than the joists themselves? How can I tell whether the problem is the joists or the floor?

If it's the floor, it seems that adding one (or two?) rows of solid blocking (as opposed to the cross bracing suggested by wildie) would be the thing to do because the blocks would add addition points of support for the floor deck. That true?

ojay - thanks for the how to on the support beam. If that's what I need to do, you have given me just the sort of info I was looking for! Perfect!

As for pics in the crawlspace, I don't have a digital camera readily available - sorry.

So - how do I figure out what I need to fix?
Well 5/8" is not a lot of support but depending on how it was installed it could be fine.

The way to see what the problem is is to get several of your teenagers on the floor at the same time close to the same place. Try to get them in the space between the joists. Then have them gently move up and down. Then have them stand over a joist and do the same thing.

There should be a difference.

If it is spongy between the joists then it is more than likely the flooring. If it is spongy all over then it is the joists.

It also could be a combination of both.

As for pictures you can use your cell phone camera. Then just text it to your email address and you can then put it on here.

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