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HooKooDooKu 01-19-2010 12:00 PM

Floor Joists of different sizes
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I recently made our living room floor less bouncy by sistering some of the 2x8 joists with 2x10 joists. The other joists, I attached a 2x4 to the bottom of the existing joists to create something of an I-beam.

The net result is that the 2x10 sistered joists protrute 1/2" farther down than the original joists with the 2x4s.

Now I'm interested in finishing the basement and I'm trying to think of ways to drywall the ceiling.

One idea that has come to mind is to simply run the drywall parallel to the joists, attaching it to the shorter joists and butting them against the taller joists. With 5/8" drywall, that would leave a 1/4" gap at the larger joists that I could mud over.

Since a picture is worth 1000 words, here's a sketch.

You can see the original 2x8 joists on 1' centers. Every third joist had a 2x10 sistered to it. The other joists have 2x4s attatched under them. To attach drywall with this idea, I would need to add 2x2 strips to each side of the 2x10s to give a surfact to attach to.

The other idea is to get some 1/2" plywood and cut it into 3.5" wide strips, and attach the plywood to the underside of the 2x4s that are laying flat to make them the same height at the 2x10s. Then hand drywall as normal, except I would use screws long enough to penetrate to the 2x4 NOT the plywood strips.

ptarmigan61 01-19-2010 01:39 PM

I would rip 1/2 plywood strips and tack them onto the bottom of the 2x4s you used to create the I joists.
I think you might be asking for trouble trying to mud over the bottoms of the 2x10s.

bjbatlanta 02-04-2010 12:11 PM

Use the 1/2" plywood and get all of your framing members even....

HooKooDooKu 02-04-2010 01:45 PM

Any thoughts on using Z channel for this situation? I've heard of it but couldn't find it in the local big box store. I'm thinking that you principally attach the Z channel to the 2x10s, then come back with longer screws and spacers to attach the Z channel to the 2x8s. Then of course the drywall to the Z channel.

bjbatlanta 02-04-2010 02:08 PM

I'd keep it simple and use the plywood...

jlhaslip 02-04-2010 04:58 PM

JB weld the 1/2" plywood strips onto the 2x's and that'll be good enough... :lol:

bjbatlanta 02-04-2010 05:20 PM

Liquid Nails, PL2000, or any such construction adhesive in a tube will work if you want to go that route. JB might be a bit pricey. Does JBWeld come in large tubes or just the small "squeeze" tubes?? Maybe I haven't seen the large tubes....

HooKooDooKu 02-04-2010 05:43 PM


Originally Posted by jlhaslip (Post 394763)
JB weld the 1/2" plywood strips onto the 2x's and that'll be good enough... :lol:

I've made sure that the 2x4s are securely fastened to the 2x8s such that I can hang drywall from them. So when it comes time to attach the drywall, I would want to use screws long enough to go through the plywood and into the 2x4. So the plywood only has to act as a spacer.

Besides, I don't want to use any sort of adhesive because then I would have to do something to hold the plywood against the 2x4s until it cured.

Since the plywood is just acting as a spacer and doing nothing structurally, I would really just want to shoot some finishing nails to hold the plywood in place. That way, the plywood can be covered either immediately, or at a later time without concern for movement.

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