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Old 06-09-2003, 04:53 PM   #5 (permalink)
james t kirk
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Location: Toronto
Quote:
Originally posted by wondash
I was also concerned about the insulation, but to add strength to the floor, I added 2x4s running the opposite direction to the joists, then laid the floor on that. This allowed enough space to keep from compressing the blown insulation. It also solved any problems with all the wires. Thanks for the feedback.
And exactly what are these 2 x 4's bearing on?

the original (lower) 2 x 4's????

That won't make a bit of difference to the capacity of the original 2 x 4's, unless they bridge the original 2 x 4's and bear on a load bearing wall.

If anything, you have just added more dead load to the already overloaded ceiling structure.

Joists, be they floor joists, ceiling joists, or roof joists are typically installed in the short direction since the stress developed in the member is a function of its length (Where Moment = (w x L^2)/8 for a simply supported member and Stress = M x C/I = M / S where S is the section modulus and is essentially a function of the geomtry of the member.) (W = Loading in pounds / linear foot, L = length, M = moment.)

Unless the aspect ratio, i.e. the Length of long member divided by the length of the short member is less than 2.0, only the short members will do any work whatsoever.

Even if the aspect ratio is less than 2.0, the long members will still require something to bear on other than the existing 2 x 4's (like another load bearing wall) And the long members will do less work than the short members regardless.

You would have been better off to fix your new 2 x 4's paralell to the tops of the original 2 x 4's with some sort of mechanical connection thereby making them into 2 x 8's effectively.

Now that would have worked.

Merely laying 2 x 4's on top of the original 2 x 4's at 90 degrees will do nothing for strength and will infact only make it worse.

I seriously recommend you rethink your strategy.
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