In article , rnr_construction wrote:

"Joe Bobst" wrote in message
...
Use pressure treated joists--they are made from a much harder, denser,
stronger grade of wood than typical doug fir.

True often but not always. The really tough PT is yellow pine, heavy and
dense. But I got some PT at my local lumber yard a while back that was
some kind of softwood from Nebraska IIRC. Not at all in the same league
as the Southern yellow pine. HTH

PT around here is all Doug Fir or hemlock
it isnt any harder at all. Often times its much weaker.

Replacing joists is probably going to be an enormous job; what's he going
to do - lift up the whole house and replace all the joists to make them
the same size?

I suggest converting the first floor / basement ceiling into a torsion
box to stiffen it. Toss up a 4x8 foot sheet of plywood under the area
that's bouncing and screw it in with drywall screws on six inch centers.
If this seems to help the problem, take it back down and put glue on every
joist before putting it back again. You're not getting this back off, so
be sure you don't cover up anything important (like a cleanout). You can
extend the plywood to cover the entire basement ceiling.

Look up torsion box on Google - the technique is used in furniture, in
interior doors and in cardboard boxes. It's probably more expensive than
using the correct sized joists in the first place, but it's a possible
fix for the problem. Use thin plywood to avoid having to lift a heavy
weight to the ceiling of the basement. Quarter inch should be more than
enough.