Hump in Floor - New Construction

[Anthony Torello]

I recently inspected a newly built (2024) home with a significant "hump" in the first floor flooring above the centerline beam. The hump is approximately 1/8" over 1' approaching the beam. This condition appears to be built into the framing, as a raised tile line exists in the bathroom above the beam as well, without cracking of the tile or mortar. This indicates to me the issue was present at the time of construction.

The beam consists of (3) 1.75"x9.25" LVL members. 2x10 floor joists lap over the beam, and blocking has been installed. Floor joists span ~15' from the beam to the foundation walls.

The blocking does not appear to have caused the problem, it is installed slightly lower than sub floor, not tight against it.

On one side of the beam, the joist tails extend past the beam approximately 6"-8", and the other side approximately 3". These joist ends are TIGHT against the subfloor, and likely causing the humped area above.

I checked the levelness of the floor joists across the span and found them to be VERY straight, without permanent deflection. No significant loads are present along the span of the joists currently, or wall loads from above.

What could have caused the "humped" area in the flooring? I have seen this detail used without a problem in the past, and after many years of inspecting I am stumped on this one.

Typically I would find deflected joists the cause of "proud" joist tails, but without significant load on the joists or permanent deflection I am at a loss.

Thank you for your input.

Tony

 

[SinStrucEng]

The floor joists - are they not showing signs of notable deflection AND they're level, or are they simply not showing deflection?

 

[phamENG]

How much of a gap between the blocking and the subfloor? Is it uniform across the whole length?

How wide is the hump?

Are the floor joists fastened to each other across the beam, or are they just sitting next to each other and fastened to the beam?

 

[jhnblgr]

Could the 2x10 be rotating in the hangers and prying up the subfloor telegraphing through to over top center of the beam.

 

[Anthony Torello]

The floor joists - are they not showing signs of notable deflection AND they're level, or are they simply not showing deflection?

Yes, they are also level across their span.

 

[Anthony Torello]

How much of a gap between the blocking and the subfloor? Is it uniform across the whole length?

How wide is the hump?

Are the floor joists fastened to each other across the beam, or are they just sitting next to each other and fastened to the beam?

The width of the humped area appears to correspond with the length between joist ends, just over 12"

The gap between subfloor and blocking is not uniform, but in all cases I could slide a 1/16" width metal ruler through.

Joists are toe-nailed to the beam, and occasionally single nailed to each other at the lap over the beam.

 

[DoubleStud]

Did they build a framed wall below the beam to the slab on grade? Maybe the soil is expansive? Not sure what level the beam is.

 

[XR250]

The joists are digging into the beam while the unloaded blocking is not. The blocking ends up being the hump.
I see this frequently - but mainly with longer span I-joists bearing on the beam.

Edit - just noticed this...
"The blocking does not appear to have caused the problem, it is installed slightly lower than sub floor, not tight against it."

Nevermind

 

[Ron247]

While the hump might be unsightly, I would expect at least a 1/16" on a foot to be present in many locations. Is there some condition that makes the hump more noticeable such as an eastward/westward facing window and a shiny floor? What explains the extra 1/16"?

I can see several possibilities, but you probably have one of those situations where there is not just one contributing factor but an accumulation of several. Prior posts have pointed out several realistic possibilities. Let me add some more of those little ones I tend to forget at times.

1. Depth of joist variance. I measured a bundle of 2x10s one time for depth because of a picky customer coupled with eastward window and shiny floor situation. It took me almost the entire bundle to find 12 joists with the same depth within 1/16" and similar cambers. Aggravating but she was a rare customer that always paid well and realized she had to pay extra for wanting close to perfection. The 9-1/4" joists ranged from 9-1/16 to 9-7/16. Try putting a 9-1/16 straight next to a 9-7/16" cambered. You will have a 3/8"+ over 16" slope.
2. Camber variance.
3. IF there is a joint in the subfloor at the hump, did a little piece of trash get under one sheet but not the other?

But I do have some questions:

1. How close is a beam support (pier I assume) to the area in question?
2. How are your beam joints spaced?
3. How did you confirm there is no permanent deflection? Did you unload the joist?

 

[Tomfh]

Joists shrunk?

 

[phamENG]

Weird - I was watching this thread yesterday and the OPs responses never came. Now, this morning, they're interspersed with responses I read yesterday...

The width of the humped area appears to correspond with the length between joist ends, just over 12"

The gap between subfloor and blocking is not uniform, but in all cases I could slide a 1/16" width metal ruler through.

Joists are toe-nailed to the beam, and occasionally single nailed to each other at the lap over the beam.

Then it sounds like it's deflection in the joists. Could be they installed them all with the lumber's spring (natural camber) going down. The light

When you say the joists were flat, how did you measure them? Did you measure the underside, or the flooring above? It's possible that the contractor made some effort to level the floor, masking any deflection that might be present on top. And for this to be all joist deflection, the slope of the joist would be in the neighborhood of 0.2%...possibly enough to fool a bubble level if a) you have any paralax error or b) it's cheap or damaged.

I prefer to see better attachment between the joists to help minimize this effect. IRC doesn't have a minimum fastener count for this, but they do for lapped ceiling joists - and it's (4) 3"x0.131" nails when it's NOT part of a rafter tie system. Seems floor joists should get at least as much to hold them in line.