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Basic Problem....

Posted by Dodgeman on December 23rd, 2001 10:36 PM
In reply to weak joists/ spongy floor by Jim M on December 23rd, 2001 09:36 PM [Go to top of thread]

Jim M,
I fear your spongy floor is not due as much from the holes in the joists as from the 2x8 joists themselves. A 2x8 joist is 7 1/4 inches deep, and if these are placed (I'm assuming)16 inches on center over nearly a 12 foot span, the deflection under load will be marginal at best.
The holes in the joists, although not ideal, will not significantly affect the deflection UNLESS there are already horizontal cracks running through the holes for some distance either side of them.
Now for a solution.... Your idea of 3/4 inch plywood (the type wouldn't make much difference) would help, but the increase in stiffness would probably be disappointing to you. A better solution would be to glue and screw 2x4's to the bottom edge of the joists. The 2x4's would be the flat way, so the joists at the bottom would look like an "I" beam. The 2x4's should run the entire length of the joist. This will reduce your head room by 1.5 inches, but would make a significant increase in stiffness. There are other solutions, but this is probably the least amount of work.
Happy Holidays,

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