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I was hoping to get some opinions on a subfloor replacement project. I am replacing the subfloor in a third floor bedroom and would like to keep the ceiling exposed on second floor below. I would like to apply 1/2 drywall on top of floor joists before applying 3/4 plywood subfloor and carpet.This would allow a finished drywall ceiling exposed between joists and eliminate trying to fit and support drywall from below. Butt joints could be concealed over joists and plywood subfloor could be glued to drywall and screwed to joists. My concerns are; does the application of drywall between joist and subfloor compimise the integrity of this connection ? Are there long term concerns with regard to floor loads or possible deterioration of drywall. The room gets light duty usage.
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Not to be negative, but I strongly urge you not to put subfloor on top of drywall, as in DO NOT! Drywall has no place as a structural element, and will crush underneath any load on the subfloor. Also, not to question your plan, but keep in mind the amount of noise that will transmit through the floor, particularly if the room above is a bedroom. If you are determined, there are two possibilities that spring to mind, excluding cutting drywall to fit between the joists (which wouldn't be that tough, if you are familiar with tear-off 'L' bead, which makes spackling up against a finish surface very easy). One would be to use a finish-grade 3/4" plywood as subfloor and turn the finish face down, and paint it. The other is a technique that would only work if your joists are bigger than normal 2x joists, and that would be to run a strip of 1/2 plywood(glued and screwed) down the center of the joist, leaving about 1/2" on either side (in other words, a strip 1" narrower than the joist itself), then set the drywall on top of the joists(in between the strips)and then glue and fasten the subfloor to the strips. I wouldn't recommend doing this on top of 2x joists because you would only have 1/2" of bearing for the subfloor, which isn't all that great. If you are unsure of yourself, talk to a professional carpenter who can come look at your situation.
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R. Kadia:
Nick has it right when he says, "do not."
If you desire to have a finished ceil'g w/ exposed flr/ceil'g joists then I would suggest finding a structural subfloor type that can take a finish like paint.
*Another interesting subfloor detail would be to use either 1X or 5/4 tongue and groove pine of either ramdom width or same with the v groove or beading installed down. This could even be finished prior to installation and make the job easier.Pad and carpet should give enough insulation, but I'd put a layer of resin paper under the pad to prevent dusting.
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I like the V-groove siding idea, or you could find paneling you like and put it down before the plywood subfloor
A layer of 1/2" Homosote does wonders for soundproofing and cushoning. Just lay carpeting and padding as you would any other floor.
John
*R.,I have no problem with what you propose. If you put down a layer of 1/2" drywall before you put down a layer of plywood decking, I see no harm. If you use a long enough screw to attach the floor sheathing (or decking as it can be called) to the joist, what harm can it do. It may add to the sound proofing, and you can finish the underside any way you want. I say go for it and enjoy.Ed. Williams
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Ed:
Surprised to hear you recommend drywall here.
Even someone completely in LOVE with drywall would
positively not want to do this. If you want the
look of drywall, just do what some of the other
guys said and lay down AC plywood or some other
paint grade sheet, either call that good as a
subfloor or add another layer on top, finish
ceiling of lower room as desired, bingo. You have
your exposed joists and a ceiling and a subfloor
upstairs, simple enough. Drywall is just asking
for lots of trouble. And think of the future
homeowners who will wonder about who would do
this.
MD
(A definite drywal
*Around twenty years ago, here in SoCal, engineers were using drywall as a shear paneling. That didn't last long! Drywall will crush, tear, and grind down under motion, whichever way the stress is. I agree with Nick....do not! I like the idea of laying a t&g, finish down, and plywood over it, or if you're married to the idea of drywall and don't want to finish it to the sides of the joists, try a molding (prefinished if you like) as a "crown" or scribe to trim off the joint between drywall and the joist. By the way, is there no electrical or plumbing in this whole system? There isn't any way to disguise that, if there is.Good luck,-Ben
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Mad Dog,
I'm sorry, but I really don't see what could go wrong. Please explain your feelings and experience with this senario.
I agree that plywood, such as AC can be finished out to look like drywall, but why not drywall.
Please explain.
Ed. Williams
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If you are sold on the idea of drywall and don't want to finish between the joists try this idea. Attach 1x 2 's to the sides of the joists with the tops of the strips held down the thickness of the drywall from the top of the floor joists. (Some form of routed edge treatment on the bottom edge of the strips would be nice). Then cut your drywall into rips that will lay on top of these 1x2's (I would recomend buying drywall as long as the joists so you have no butt joints to deal with. After you have have installed the wallboard you can place your subfloor in the normal way and you will not have to worry about the wallboard crushing as it will not have any weight on it. Just be carefull when walking the joists not to put afoot thru the board!! Hope this idea helps you out.
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I'd be concerned about the drywall over the floor joists being crushed. There is a technical term called compressive resistance or something like that (I think of it as squashability) and drywall doesnt have much. i.e. If you take a 1 1/2 " strip of drywall, osb and plywood and jump up and down on them or stick them in a vice, the osb and plywood will come through pretty functional but the drywall will be reduced to dust.
Now drywall certainly has some squashabilty and maybe with the load being spread out by the subfloor above its enough, but I'd still be concerned.
If you're really set on doing this, maybe you could run a little experiment if you're not in a rush. Throw a piece of sheetrock down on the floor joists and screw a piece of plywood over it. Then pay a fat kid to dance on it for an hour or two a day for a week or so. You get to feel like a real "building scientist" type gathering empirical data in the field and the fat kid makes a few bucks.
JonC
*Sounds like a good time to use 3/4" one sided MDO to me. Install it good side down. Treat the bottom just like drywall and your subfloor is already in too. Couldn't cost much more than drywall AND underlayment and there wouldn't be any question about the integrity of the material. - jb
*I'll buy that for a dollar....Good idea Jim.Ed. Williams
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Ed,
My concern was twofold: I believe the drywall would crush. I
also would be paranoid about spills, open windows in rain,
or a possible roof or plumbing leak-then what? If the drywall
fails, your subfloor is now supported by the screws, sort of
floating 1/2 inch off the joists. Don't forget, each screw driven
through the drywall creates a weak spot where crushes would likely
start.
Still think it's a really bad idea,
Mad Dog
xxxxxx
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Mad Dog,
I think you're right. I change my opinion. After second thought, it's probably not a good idea.
Ed. Williams
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Aw Gee Ed,
Don't give me any credit, I know you knew better all the time!
-Dog
xxx
*R.Kadia,Just a thought here-I'm wondering if you felt it was okay to do this because currently the room gets "light duty usage." Remember to consider the future owners/users.I have done enough remodeling that shouldn't have had to, because the former work was not done "right" or took too many chances, or cut corners. I know this will seem arrogant, but I feel that all three of these considerations apply to your idea. On the plus side: you were thinking ahead and trying to get two for the price of one. I like that train of thought. And you found, I think, a good place to ask your question. Just my 2cents.Good Luck,Mad Dogxxxxxxxx
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I was hoping to get some opinions on a subfloor replacement project. I am replacing the subfloor in a third floor bedroom and would like to keep the ceiling exposed on second floor below. I would like to apply 1/2 drywall on top of floor joists before applying 3/4 plywood subfloor and carpet.This would allow a finished drywall ceiling exposed between joists and eliminate trying to fit and support drywall from below. Butt joints could be concealed over joists and plywood subfloor could be glued to drywall and screwed to joists. My concerns are; does the application of drywall between joist and subfloor compimise the integrity of this connection ? Are there long term concerns with regard to floor loads or possible deterioration of drywall. The room gets light duty usage.