I'm confused - were the walls you removed on the same level as the floor which is bouncing, or below? If they were on the same level, even if the walls weren't load bearing, they may have (unintentionally) been stiffening the floor by pulling down on the ceiling joists....others will probably know more about this than me.

Load bearing or not, the other factor is I suppose the dampening effect walls have across a structure, it's probably like a drum skin- more vibration if it's uncovered, if you lay material across it, it dampens it.

Is there access from below to the bouncy floor? Sistering some joists or adding additional support from below might be an option.

Thanks for the response! Yes, floors I removed were on the same level as the floor that is bouncing. And, no, I don't have access from below. This is a bi-level -- you enter the house on the ground level; a few stairs up brings you to the main living area and a few steps down brings you to family room and extra bedrooms.

At any rate, you raise a good point about dampening. When we removed the kitchen and dining room walls, we were only concerned about structural issues (e.g. were they load bearing). We didn't give any thought to how the wall removal would impact floor stability. Yikes.. not really sure what to do now....

The floor you describe is one of those that meets the requirements of the building code but is not stiff enough to be comfortable. This is why no one should use the building code as a design guide.

Removing any walls could easily have allowed the floor to deflect and shake more freely. I don't know why that would happen without someone walking across the floor unless there is a mechanical system in contact with the structure.

There's not much you can do without opening up the ceiling below to add reinforcement but first I would try turning off all mechanical systems to see if that helps.

I'm envisioning that there is a 12 ft span on either side of the house so you've got a 24 ft clear room now with a support beam between bays below. I'm pictyuring the wall that was removed to be on top of the support beam dividing the spans. Witht he wall in place you get some passive end fixity of the joists and when it was removed the support gets closer to a simple support allowing the floor to deflect more. I cjust can't see this being a huge difference but it would change things a little.

When you put new hardwood down, did you remove the old floor on top of the joists of just go over it?

Like Mightyanvel said, a constant low level vibration is usually associated with a mechanical system of some sort. Refrigerator/wine cooling chest/HVAC equipment. Try switching potential sources off systematically and see if you can isolate the cause.

Is the "ground level" truly a slab on grade or is there a crawl space? Most direct solution is to open the floor and put another support in cutting the span in half.

Good luck.

mightyanvil and sdello,

yes, you've got the set-up just right.

I removed an old wood floor, and put down new hardwood. We didn't replace the subfloor, which might have been a mistake.

Can't think of new sources of vibration, but I will test that theory by switching sources off sytematically.

Ground level is a slab -- and a living area -- so adding a new support is not easy. But, if we continue to be bothered, we'll have to bite the bullet and open up the ceiling

I greatly appreciate your feeback. Thanks to you both. At the very least, you've reassured me that I'm not going to go crashing through the floor...and I've learned my lesson to never buy a fixer-upper again!