Floor Joists Leaning and Floors Bouncy

9 years ago

cross-posted from Remodeling:

Wood frame house, two stories, about 18 years old (so legal, har har). Foundation is full basement poured concrete.

For some reason, I've noticed a increase in the bounce of my floors, and general vibration caused when someone walks across them. Today I got the bright idea going in the unfinished portion of my basement and checking how straight the floor joists are. These are enginereed i-joists. I put a right angle on the underside of the subfloor, and butted against the top edge of the i-joists. The bottom edge is almost 1/4 inch away from the straight edge. It seems that all my floor joists are leaning a good deal and I guess this is cause of my bouncing floors. Sound plausable?

What would cause this? Foundation shows no cracks and is in good shape all around. I have 2 ideas, but I know little about construction and I'd like to hear from some pros before I start with my theories.

Thank you for reading this and I could use some help!

Comments (7)

millworkman
9 years ago
Pictures?
grubby_AZ Tucson Z9
9 years ago
Ditto. Especially the ends and any sort of joist-to-joist bracing that may be there, or any feature that may tie any two or more joists together at the bottom. Sizes? Spans? All tilted the same direction?
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handyhusband
9 years ago
First a questions? Is there any bracing perpendicular to the jousting? It would seem that only 1/4"lean would not be the cause of the bounce. However if the span is to great for the size of joisting this will certainly cause a bounce. If there is no bracing, bracing will help. But with the type of I- Joists it sounds like you have each manufacture has very specific ways they want their product braced. So flirst check your joist size and spacing to make sure they are not over spanned. If not some bracing should help. I am a licensed contractor and have found over spanning or over spacing or both to be typical. Makes you wonder how they pass inspection.
bus_driver
9 years ago
For maximum rigidity and strength, any joist must be vertical. Engineered joists and trusses are especially affected by this consideration. The 1/4" you mention should be evaluated by an engineer with the idea that it needs to be determined if they were originally installed this way or if they have shifted since the house was completed. If this was my house, this would be high priority.
FranW01
Original Author
9 years ago
The question is, what could cause them to shift?

They very well might have always been like this, but then what would account for the increase in floor vibration that I've noticed?
FranW01
Original Author
9 years ago
There is no bridging, but some 2x6s are attached to the subfloor between the upper flanges. This was done to eliminate some floor squeaks. There is also at least one piece of lumber attached pendicular to the joists, nailed into the underside of the joists. I presume a previous owner did this to reduce bounce.
handyhusband
9 years ago
Most likely the 2x6's were meant to take the place of bridging. To hold the the joisting in the upright position. I would inspect the joisting while you have someone walk on it and see if I could detect any obvious movement in the joist components, ie are the engineered joists still firmly glued together. Also has the live load changed? Most floors are designed to bear 40 lbs per square foot minimum live load. Live load equals anything placed on it,furniture etc. . 20 lbs per square foot dead load the weight of the floor structure itself.