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rising floor...

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SLTA

SLTA

Structural
Joined
Aug 11, 2008
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I looked at a house built in 2007, where there appears to be a growing hump in the first floor. Floor joists (TJIs) run parallel with a CMU wall that has a little wood stem wall above it and is in place of a TJI at that spacing location. The wall below doesn't line up with the wall above, of course. The TJIs are level - they don't appear to be deflecting much at all, according to my 4' level - but there is a definite upward hump over the length of the stemwall/CMU location. There is no obvious movment of the wall, or cracking in the CMU, or swelling in the stemwall, that could be seen from below in the unfinished basement space. We don't have swelling soils around here.

Anyone have any idea what's going on with this?

Please remember: we're not all guys!
 
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Obvious hard point/line in the floor system relative to the floor joists.

Can you post a plan of the floor framing system with the miss aligned stacked walls showing too?

Mike McCann, PE, SE (WA)


 
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You asked for it - my AMAZING drafting skills, in action. TJIs are 16" deep and 16" oc. Wall is 8" unreinforced CMU, not retaining. This is one of those crazy McMansion-type houses that was built when the county didn't have time to inspect every house during construction, so there's flat no telling what's happened.

floor_joists_hclhwa.jpg


Please remember: we're not all guys!
 
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Is the rise roughly consistent along the span of the TJIs? If so, I would suspect that the bearing walls have settled, but the NLB CMU wall hasn't. Thus the "rise" in the floor system at that point.
 
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The rise appears to be greater near the middle of the span of the parallel wall. There is no indication of differential settlement between the CMU wall shown and the exterior bearing walls (no cracking, etc).

Please remember: we're not all guys!
 
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You have a relative stiffness issue with the hard bearing line of the CMU wall below compared to the stiffness of the parallel joists, and you are reading the deflection of the floor joists at midspan. That is the reason that it seems like the center of the CMU bearing wall is lifting. It is all relative.

Mike McCann, PE, SE (WA)


 
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Span of the TJIs?

Have you set up a laser level and checked the bottom chord of the TJIs for deflection. Not noticeable to the naked eye on the bottom is still enough for a noticeable hump in the floor above.
 
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That's what I figured - just wanted to make sure I wasn't missing something big.

Now - what do I tell them to do about it? I'm considering stiffening the floor trusses, perhaps jacking them with a beam.

Please remember: we're not all guys!
 
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jayrod12 - didn't yet. I checked with my level, but I think by the deflection pattern that you're exactly right.

Please remember: we're not all guys!
 
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Does the wall provide lateral support? Is the wall above load bearing?

If the answer to both of those questions is no, then I would look at providing supplementary wood members on either side of it, and removing the cmu wall.

If either of those answers is yes, then there aren't really any feasible options. It's a poor design layout.
 
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Removing the wall isn't really feasible, because one side is unfinished but concrete floor for storage but the other has just raw soil cut away at this wall. I agree - totally a poor design.

Cheers, folks, and thanks for the help.

Please remember: we're not all guys!
 
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Or you could replace the CMU wall with a beam under the wall above of the same EI and overall deflection characteristics as the floor joists...

Or, if the floor joists can tolerate it, add a transverse beam supporting the TJI's at midspan, framing to the CMU wall footing and whatever beyond.

Mike McCann, PE, SE (WA)


 
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Complete removal isn't necessarily required, just enough removal that the wall no longer supports the floor. Take out the top course. It could still act as a demising wall.

This is all of course subject to seismic and stability detailing depending on the location.
 
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SLTA said:
a CMU wall that has a little wood stem wall above it and is in place of a TJI at that spacing location
Click to expand...

Seems that the CMU wall below has a small stem wall on top of it, that is now load-bearing.

Can the "little stem wall above" the CMU wall be removed to temporarily (permanently?) 'de-load' the floor system at this location and be rid of the 'bumb'?
 
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Ingenuity - it could be removed, except that it's also in place of one of the TJIs at that spacing location. I think I'm going to have to tell them to deal with it.

Please remember: we're not all guys!
 
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Does the deck/sheathing cantilever to support the wall above? If yes, could the CMU wall below flat and level while the wall above is causing the sheathing to deflect creating the hump?
 
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Not likely at all. That would be very non-standard framing.

Mike McCann, PE, SE (WA)


 
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