Thread: Hump where main support beam is located

Did an inspection today and ran across something that I cannot figure out. This is a bi-level house where there is a very noticeable hump on the floor where the main support beam is located. Carpeting on the main level and the main support beam with heating trunk line boxed in with drywall (Floor joist/support beam or sub-floor could not be seen). The hump is around 10 inches wide and only goes 1/2 the length of the house (around 15 feet) then becomes flat. A small part of the floor joist that can be seen (on the other side of the house where the main level floor is flat) showed proper installation of floor joist. The floor joists are 2 by 8, 16" o.c. installed on top of the metal main support beam.

I first thought of sagging but when I saw the small are where the 2 by 8s were installed on top of the main support beam, it was hard to believe that a 10 inch wide hump would result. There were no cracks or patching found anywhere on the walls or ceilings including where they come together.

Attached is the layout of the house.

Any thoughts?

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Would this happen to be a modular home?

Also if the floor joists were not cut back to the beam and extend out past the beam that could result in a high spot. Hard to ascertain if the ceiling is finished.

quote=Raymond Wand

Would this happen to be a modular home?

No.

I was told that the house was built in the 1960's if that might help.

Also if the floor joists were not cut back to the beam and extend out past the beam that could result in a high spot. Hard to ascertain if the ceiling is finished.

Properly cut at the area where visible (located on other side where hump was noticed). The hump being 10 inches wide only?

Well, that would rule out that theory.

Cheers,

I suspect that it is not a case of an actual hump so much as it is a dropped floor to either side of the beam because the joists beside the beam have shrunk or dropped. If the joists were originally installed flush with the beam up at the top, they may have shrunk more than the beam, leaving a gap beside the beam on either side -- and the appearance of a raised area. Or they may have been installed with a ledger which has dropped. In either case, the appearance would be the same. Is this area over a garage with a beam breaking the span?

Oops--
I just saw where the main support beam is metal, not wood. If this is true across the area with the problem, I suspect that the joists have deflected, and the ends over the beam have kicked up slightly. This would leave a ridged area down the center line and a sunken area to either side of it along the length of the beam.

Kevin Barre

This would leave a ridged area down the center line and a sunken area to either side of it along the length of the beam.

I can't see it being anything else. I was focusing on three things during the inspection to help me determine reason; the lower level ceiling and the upper level wall to see if there was sagging/cracking/separation that was patched. Visually, I couldn't see anything.

Like Kevin B, my best guess is that the floor joists in that section are over spanned and run a bit long where they lap on top of the beam. Deflection of the joists is causing the tails to kick up, creating the hump. You say that the portion that is visible looks OK, but that's in the part of the home where there is no hump. Obviously, there is something different going on in the part of the home with the hump. You are not likely to be able to determine the cause without doing an invasive inspection.

In my opinion if there are no other visual clues, i.e. cracked walls, out of square door frames, then this is likely something that will remain is an inherent feature of the house due to...floor joists, beam, improper loading in that area?.. who knows. If in doubt I would be sure to recommend they consult a structural engineer to satisfy themselves everything is honky dory.

I would also be sure to write in the report that the purchaser query the vendor of this concern as to provide a historical perspective or knowledge.

Cheers,

Fwiw,

I see this type of condition from time to time. The last time was about 6 months ago. Twenty year house with hump located in hallway from kitchen and right above the main beam. Basement ceiling finished. Door frames square.
I have also seen humps in modular homes in beam areas where they put the two halves of the house together fwiw.

I know it's on both sides of the wall, but... some version of excessive joist overlap at beam/girder?

Originally Posted by Brandon Chew

Like Kevin B, my best guess is that the floor joists in that section are over spanned and run a bit long where they lap on top of the beam. Deflection of the joists is causing the tails to kick up, creating the hump.

I agree with Brandon.

Do I win a prize? I suggested that in the first place!

Is the roof structure stick built or truss? Are the the hallway walls offset from the center beam? This is a real common thing if the walls are load bearing. The load path is offset, thereby causing the floor joists to sag from the load. As the floor goes down it seems that the beam is humping, when in actuallity it has not changed.

The critical thing is to always follow the load path.

I have this very issue in my own house built in 1953. One hallway wall is offset 12" and the other 26" from the center of the beam. It appears that the beam area hump is 3/8" higher than the the hallway edges. I pulled a string on the beam and it is perfectly straight. I pulled the string on the floor joists and the sag was very obvious. With out stretching a string line the sag was not visible to the eye.