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Unread 11-26-2017, 09:34 AM   #4
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Join Date: Jul 2001
Location: Boerne, Texas
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Originally Posted by Dan
Seems the 3/4" ply would be the way to go; flat, straight, strong, and easier to work with.
You forgot to mention, "and ineffective," Dan.

If you're sistering to reduce deflection, you'll want to use the 2x material. If you'll evaluate your nominal 3/4" plywood, considering a 5-ply material, you'll see that you'd be adding only about 3/8ths" of material in the correct orientation. The remainder will provide only filler material.

If you want more strength and rigidity, I'd recommend you sister with 2x material, properly installed with adhesive and mechanical fasteners. Or, if you can support each end of the sisters, you could just add new joists midway between the existing to reduce the between-joist spans.

You'll also want to be sure the overlapping ends of your joists at the center support are well fastened together to reduce the cantilever effect of loading near the center of each joist span.

My opinion; worth price charged.

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