I watched an old TOH classic where their plumber used strongbacks
on his own house. 'Twas steel plate bolted through the joists. They
jacked it up to remove the sag, drilled, bolted, and let 'er down.

Hey - I remember seeing that now that you mention it. (very few of
those that I haven't seen at some point). There were a couple of
structures where they replaced or added a big beam, but I remember them
adding steel alongside existing joints in once case just to stiffen the
floor. Steel was used because you would flex as you put it up into
place and then turned on edge, bolted, etc it would stiffen the joist.
Used 1/8" plate (probably 10ga) if I remember correctly. There was also
an episode where they ripped up the floor (to preserve the ceiling
below) and sistered in glu-lam joists to repair plumber work.

That or a post or two would go a long way toward reducing dish
rattling until:

A) you get dem wildarsed kids under control
OR
B) they grow up.

Posts are out - space below there is supposed to house my pool table
someday soon.

Getting the kids under control.... yeah sure..... besides what happens
if the "kid" is me sometimes?

Some days it seems like the kids will never be growing up. Besides
about then there are grandkids (just ask my parents)

grin

Dan