weight suspended from I-joist ceiling

I want to soundproof my basement as much as possible. I will be moving a band in to rehearse and I want it to stay quiet as possible upstairs, this is my #1 priority.
My plan is to stuff the cavities between the joists with fiberglass batting, I assume a higher R rating will be better? After that, I'd like to run rubber strips or something along the bottoms of the joists, then screw 2 layers of drywall to it with a layer of 'green glue' in between. I know it won't be silent upstairs, but this would be an acceptable level of soundproofing for my purposes.
My concern is that the joists are not standard 2x12's or whatever, they're I-joists - 2x3's on the top/botton, and what looks like a 10" or so strip of Norboard in between. I was told a year ago not to hang weight from the bottom of I-joists, because while they're strong when you push on them, they are NOT strong when you PULL on them.
So, by my guesstimates and calculations - lets say a sheet of drywall is 40 lbs. 2 sheets thick is 80 lbs every 4x8 section, which is 2.5 lbs per sq. ft. That's a total of 750 lbs if drywall on the whole thing. All that batting is going to add weight too, not sure how much, maybe 100 lbs?
Will this be safe? Any alternatives?
tia,
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The weight is not a problem. You have two concerns - noise transmission by air and by structure. You should DAGS on some alternative methods, such as using resilient channel attached to the I- joists. The resilient channel acoustically isolates the structure from the ceiling covering. Sound absorptive material on the room side of the ceiling will reduce the amount of noise vibration getting to the structure.
R
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You are OK. Lots of new homes use those joists and many have finished basements with drywall ceilings. Maybe double up on the screws to spread out the load.
There is a type of fiberglas insulation that has acoustic in the name, forget exact term, that may give you better sound suppression. I think it was white color. The heavier the insulation the better the sound suppression. Mass absorbs energy so the more mass the more sound energy absorbed.
I have a home theater in basement of new home and used sound suppression tiles in a drop-down ceiling. It is only partially effective and was an extra cost, about $1500, over drywall. I didn't want to pay double again for what were advertised as more effective tiles. Your idea is just as good and probably more effective.
Sound travels somewhat like water - it will leak out wherever it can, so you would get some benefit by plugging gaps around doors to the basement. Try any gap filler but weight of the material is the key - light foam isn't helpful. Heavy ribber strips would do it.
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sprayed expanding closed cell foam will seal better.
sealing all the holes that can allow sound transfer is critical.
then use special sound deadening drywall on isolation strips.
dont forget too much volume can do long term damage to your hearing
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I did some googling, I like the closed cell foam a lot, but it is about 2 lbs/ sq ft. That's going to add an additional 600 lbs to my ceiling if I pack the joist cavities completely. If I still go with the double drywall, the ceiling will now be supporting about 1300 lbs. I see the OPEN cell foam is more like .5 lbs/sq ft, and they claim it is also very good at absorbing sound. That would only be about 150 lbs vs 600 for the closed cell..
I'm also finding things like rockwool used for sound absorption, and rigid fiberglass panels like Owens Corning 703/705. I'll definately be looking into resilient channels too. Maybe 1 layer of drywall on resilient channels, that would get rid of something like 300-400 lbs. Of course, if it isn't an issue at all, the extra drywall would help soak up some extra sound..
The joist cavities are about a foot deep, and I'd like to pack as much sound absorption as possible into there. How much weight can be hanged from I-joists? Are my concerns about weight totally invalid? I know ppl drywall ceilings all the time, but thats just ONE layer of drywall, a few hundred pounds, vs the foam/insulation and double drywall that will be about 1000 lbs more than a typical ceiling.
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I think the loading limits for particular joist materials is listed in the building code but I do not have a copy. Try the checkout line at HD or a library or maybe search google longer than the 2 minutes I tried. or this bit more user friendly publication http://www.codecheck.com/cc/index.html
There are many techniques for sound isolation (and many places to read about it in detail) but I think a combination of stuffing the joist spaces with high density filler, caulking all air leaks and using a double layer of drywall layed in alternating directions with a small air gap between. Dispite the weight, tieing the joists together with drywall will actually strenthen the floor system. Unless you also plan to fill the room above with people you should have no problem with your plan IMO.
Additionally you can hang sound baffels on the walls, these look like office partitions mounted on the wall with 2" spacers. They should be placed to absorb sound reflections.
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Why not hang the weight on the floor above the joists? That would ensure a much better distribution of the stress.
On Fri, 13 Jun 2008 09:06:10 -0700 (PDT), mfreak

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I think your weight concerns will work out Ok. Structural calculations use design loads of 25 to 50 lb/sq ft and all you are adding is 2 lb/sq ft. This is well within allowances.
The foamed in place stuff would absorb quite a bit of sound but since the mass is low it would not absorb a lot more than other things. It costs around $1.25 a board-foot so 10 inches would be $10/sq ft - sounds like too much to me. I think you would get good benefit for only 4 inches thickness - $4 to $5 a sq ft. The foamed in place stuff adds structural strength so it may be a wash, especially if you foam all the way out to the supports.
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There is fiberglass insulation for noise reduction. Research the drywall instalation, nailing to wood transmits sound, sound proof rooms "float" they are not attached. Maybe rubber washers will help to isolate drywall. Foam will make it worse in certain frequencies since it is semi solid and will vibrate. Google soundproofing
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So your ceiling is 300 ft^2. The density of closed cell foam is typically 2 lbs/ft^2, so you'd be applying it 12" thick? That's way overkill, and the cost of 300 ft^3 of foam would be something like $3000. You might consider applying it 2" thick. Be sure to use a fire-rated foam (ASTM E-84).
Cheers, Wayne
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the basement cieling is also the floor above.
you could check with a structural engineer but i doubt the weight your adding is a issue
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