"DD_BobK" wrote in message
...
On Jan 11, 7:57 pm, Limp Arbor wrote:
My house was built in the 1970s when apparently there was a huge
shortage of either lumber or smarts.

2x8 joists, 12" O.C.,14' span
1x3 X bracing in the center of the span
1/2" plywood subfloor nailed with spiral nails - no glue
Oak hardwoord floors nailed perpindicular to the joists - the flooring
is short with most pieces less than 3'
Easy access from below in full basement

Floor bounces noticeably from normal walking, knick knacks rattle,
etc,

I tried on the other side of the beam with 16" O.C. 2x8 joists solid
blocking with little success.

I've seen 3 suggestions and want to know if anyone has tried them and
what the result was

1 Metal X bracing installed on either side of the current bracing
(splitting the difference between the center and the ends of the
joists)

2 Sistering the joists with glued & screwed plywood on both sides
(All plumbing & electric are either below the joists or parallel
to them)

3 Installing a plywood 'ceiling' in the basement glued & screwed to
the bottom of each joist.
(I guess the idea here is to make the whole joist sytem a giant
torsion box)

LA-

Your floor system is a bit a "skimpy" side.....1/2" plywood & 2x8
joists.


If oyu do decide to sister the joists.....I would highly recommend
propping the current joists with a series of jack stands to relieve a
bit of the load and to make sure the new wood take some of the dead
load.

I would glue & brad nail (or staple, M2 type) the hell out of the
sister. Adding 3/4" plywood sisters to each side of the joists would
pretty much double the floor stifness. Adding a single 2x10 per joist
would nearly triple the floor stiffness.

If you want to get fancy & minimize wood cost....you could add a 2x4
(flat) to the bottom the existing 2x8's. Thus making a T-beam.

I have done this to a joist that the HVAC people cut most of the strength
away to fit a duct in a difficult and tight area. I ran a 1 1/2" wide by
1/8" deep dado down the length of the 2 x 4 so it would easily fit on the
bottom of the joist as I was working alone. I added a good quantity of glue
into the dado and drove a screw about every 12 inches through the flange
into the bottom of the joist. Worked great, added a lot of strength and
stiffness to the joist.