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weight suspended from I-joist ceiling mfreak 06-13-2008
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Posted by mfreak on June 13, 2008, 10:26 am
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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Posted by RicodJour on June 13, 2008, 10:52 am
> 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?

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

Posted by Reno on June 13, 2008, 10:57 am
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.

Posted by hallerb@aol.com on June 13, 2008, 11:08 am
> 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 goo=
d
> 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.

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

Posted by mfreak on June 13, 2008, 12:06 pm
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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