Replies

1. 
   sungod | Jan 08, 2004 06:54pm | #1

   Install plywood across the joists from underneath.  The joist are springier in the direction across the joist because the bottom of the members spread.

   Install the first sheet in the middle of the room and jack it up a bit.  The thicker the ply the stiffer it will be (cost a hella lot more).

2. 
   csnow | Jan 08, 2004 07:04pm | #2

   Assuming floors are basically level and structurally sound in a 15YO house, the simplest method is generally doubling the joists with sisters. They probably do meet code as they are, which allows for substantial deflection.

3. 
   Piffin | Jan 08, 2004 07:07pm | #3

   As you can already see, you are going to end up with about twenty different ideas here about what is 'best'.

   That is because there is a great lack of information given so far about what you already have. layout, joist sizing, beam locations, type of joists, etc.

   After seeing where the weakness exists, then somebody can make a reasonable suggestion how to improve things best.

   .

   Excellence is its own reward!

4. 
   BossHog | Jan 08, 2004 07:10pm | #4

   The simplest thing is probably to add beams. But that cuts up your basement with more posts.

   Sistering the joists with deeper ones can also work. But often you have mechanical stuff in the way which can make it difficult.

   What joist depth and spans are we talking about?

   There is no idea so good that everyone benefits.

5. 
   muttface | Jan 08, 2004 09:34pm | #5

   A guy on another BB had suggested gluing and screwing 2x4s along the length of the bottom face of the joists for a similar problem.  The 2-by's 3-1/2" face would mate with the bottom of the joist, essentially creating something like a mini I-beam.  The guy that posted it (on the JLC site?) claimed that his structural guy had approved it and said it was a good idea.  Makes sense provided you use some beefy screws and a good adhesive.