Just spoke to my builder, who had just spoken with an engineer. He said that the span in my basement is too large to support double drywall on the ceiling.

What is the second best option? He mentioned increasing to R30 insulation and/or adding 'Celetex'. Anyone have any thoughts or similar experiences?

Thanks.

I'm not a contractor but that sounds suspicious. 8' 1/2" panels weigh about 55 pounds which is only 1.5 #/sf. If you're that close on your engineering you've got bigger problems.

Of course I could be wrong! :D

What about QuietRock?

I agree with Phil. I've got double 5/8ths everywhere in my HT, including the ceiling. (with QuietGlue in-between) Sure glad I didn't have to wrestle those 12ft sheets of 5/8ths up to the ceiling! My drywall guys were awesome. You've almost definitely got bigger issues if they won't do it. Seems odd to me.

Bummer. I think it is spelled celotex, and there are different products by that name. If they mean 'soundstop', look at this link:

http://www.knightcelotex.com/pages/soundstop.aspx

They claim an STC of 42 when installed behind drywall. Looking at the green glue site, a normal double side stud wall is 40, adding double drywall to one side gets you 42. That tends to make 'Soundstop' sound about equivalent to another drywall layer.

However, it presumably has less mass (else you'd have the same structural problem).

Adding gg between the double drywall layers pops you up to 52. Total unknown whether that will help with Celotex.

Good luck.

I'm not a contractor but that sounds suspicious. 8' 1/2" panels weigh about 55 pounds which is only 1.5 #/sf. If you're that close on your engineering you've got bigger problems.

Of course I could be wrong! :D


It actually is a pretty big span. The room is approx 18x29 with no center support posts which is over 500sq/ft of open space. The house is fairly well engineered so at this point I am trusting their statements.

I had been planning on 2 sheets of 5/8" drywall which adds weight above the 1/2" you mentioned above.

Bummer. I think it is spelled celotex, and there are different products by that name. If they mean 'soundstop', look at this link:

http://www.knightcelotex.com/pages/soundstop.aspx

They claim an STC of 42 when installed behind drywall. Looking at the green glue site, a normal double side stud wall is 40, adding double drywall to one side gets you 42. That tends to make 'Soundstop' sound about equivalent to another drywall layer.

However, it presumably has less mass (else you'd have the same structural problem).

Adding gg between the double drywall layers pops you up to 52. Total unknown whether that will help with Celotex.

Good luck.

I know nothing about Celotex (yet) but is it possible to put something like Green Glue between 1 layer of drywall and a layer of Celotex or is it specifically meant for drywall layers?

Overall this sux as I had done so much research assuming that I could do the drywall. So far my builder is one of those 'sure I can do that' kind of people so I have no reason to think that he has any alterior motives to this.

What about QuietRock?

I am starting to revisit this as well. Based on prior research I had rulesd it out, but does anyone have any real world experience with this? Anyone have any thoughts on using Quiet Rock along with Celotex?


Sorry for all of the msg blasting but I feel like I am starting at square one again, but with much less time to decide. BTW, this board is awesome with the wealth of information and experiences from you folks. Thanks again for all of the help.

Silly question, but why not do something to help support the span?

Silly question, but why not do something to help support the span?

I thought about that, but I would hate to have to put a support beam in the midel of the room as it would make the space less usable.

Why don't you use GG and 1/4"? So is your limitation stud spacing I assume? You could always run firring strips perpendicular to the cieling runners and add a layer of 1/2 quiet rock that way.

My guess is that you have a lazy contractor.

Hey, dumb question - but, I was wondering about this very same thing (putting lots of heavy, double drywall layers above people's heads)..

Why does SPAN (of the room) have anything to do with whether or not this is feasible or not? Drywall goes up in sheets..that aren't "connected", right?

Now, if you were hanging a single, 18x29 piece of sheetrock, I could understand their hesitation/concern..but, lots of 4x6 (or whatever) tiles..

Not sure I follow..

- J

I think he's more concerned about the weight of the sheetrock... not the size.

Hey, dumb question - but, I was wondering about this very same thing (putting lots of heavy, double drywall layers above people's heads)..

Why does SPAN (of the room) have anything to do with whether or not this is feasible or not? Drywall goes up in sheets..that aren't "connected", right?

Now, if you were hanging a single, 18x29 piece of sheetrock, I could understand their hesitation/concern..but, lots of 4x6 (or whatever) tiles..

Not sure I follow..

- J

I think his point is the amount of weight that the ceiling structure would be supporting given that is is large unsupported span.


Why don't you use GG and 1/4"? So is your limitation stud spacing I assume? You could always run firring strips perpendicular to the cieling runners and add a layer of 1/2 quiet rock that way.

My guess is that you have a lazy contractor.

A valid point, anyone have any thoughts on the quality of sound deadening if you decrease the thinkness of the drywall (ie 2 - 5/8" down to possibly 2 - 1/4") versus going to different products?

He never said that he could not use Quiet Rock, I had just heard that the results with that product were questionable. If it works I would certainly be willing to go that route.

I would agree with the laziness assessment, but he said he can definitely do it on all of the walls, so he would not really be avoiding that much work if he only skipped the ceiling.



This is all very frustrating given that I did not have a back-up plan.

But isn't double drywall w/GG and RSIC clips pretty much the "standard" here for ceiling construction? Seems like I've read a lot of threads where this is what people have done..but I don't remember the sizes of their rooms.

What's the range of room sizes where this will "work" and be structurally sound? My room is about 13 x 23..does that mean I also have to find another option?

Think of it this way, the weight of double 5/8" alone would be 2297lbs. Add to that the weight of the mud, tape, screws, paint/fabric, cabling, conduit, green glue, projector, etc, and it is just like parking a car on your ceiling. ADD TO THAT whatever is above him (flooring, people, kitchen? piano? beds?, etc), and now you have the equivalent of two cars (or more) parked above your head with nothing to support them but the wooden floor joists.

Edit - it all depends on the load chart of your particular floor joists, their size and spacing. Apparently this is too large a span to be unsupported and try to do DD with your particular joists. One way to add strength without using an I-beam support is to add additional floor joists (lessening the OC spacing)

So I still have a few open questions...

1) If the builder says using thinner drywall is OK, will I experiecnce a significant gain with 1/4" drywall separated with GG, or is this starting to be a waste?

2) Anyone have any experiencethoughts with QuietRock 525 or 530? I realize it is expensive, but if I only use it on the ceiling it should not break the bank.

3) I gather from reading other threads that Celotex products are fairly useless, but is it possible/useful to put a layer of GG between sheet rock and Celotex? Or will celotex absorb the GG?

Again, any thoughts, ideas, or opinions are appreciated.

Depends on what the structural engineer working with your builder says, but you may get by with thinner drywall. I wouldn't recommend 1/4" especially on the ceiling as it flexes and bends so easily (will sag). I would go with 3/8" at a minumum. The standard weights of drywall (single layer) are
1/4" - 1.2 lb/sq ft
3/8" - 1.4 lb/sq ft
1/2" - 1.6 lb/sq ft
5/8" - 2.2 lb/sq ft

Ted White or Brian Ravnaas may be able to provide you with the effects of going with double 3/8" has on STC. It seems like I read in a thread where one of them (or maybe it was Basement Bob?) did provide the numbers on this.

I have not used quiet rock so I can't comment on it's performance, though the weights of it are

525 - 2.3 lb/sq ft
530 - 2.8 lb/sq ft

Using GG between Celotex and drywall will have little to no effect as Celotex has very little mass.

So what the builder and engineer are saying is that if you have a big party of 20 or so guests ( roughly same weight as DD ) and they happen to be gathered in the rooms above, that the floor will collapse ? :eek: Yeh, right. :rolleyes: Sounds like either a bogus excuse or poor engineering/building in the first place. Can you tell us what the floor joists are ? I'm no engineer, but in my experience with having owned several houses and having gone through the build process with a good builder, a joist ( engineered TGI joists or dimensional lumber ) to span that 18' distance should be something more robust than just the average, typical joist. It's not uncommon in the building trades for builders to scrimp and save everywhere and try to get by smaller and cheaper lumber. I prefer to overbuild, but not everyone has that option or is willing to pay for it.

Just my $0.02.

Bill

So what the builder and engineer are saying is that if you have a big party of 20 or so guests ( roughly same weight as DD ) and they happen to be gathered in the rooms above, that the floor will collapse ? :eek: Yeh, right. :rolleyes: Sounds like either a bogus excuse or poor engineering/building in the first place. Can you tell us what the floor joists are ? I'm no engineer, but in my experience with having owned several houses and having gone through the build process with a good builder, a joist ( engineered TGI joists or dimensional lumber ) to span that 18' distance should be something more robust than just the average, typical joist. It's not uncommon in the building trades for builders to scrimp and save everywhere and try to get by smaller and cheaper lumber. I prefer to overbuild, but not everyone has that option or is willing to pay for it.

Just my $0.02.

Bill

After speaking to the builder I think it is the combination they are worried about. Meaning we put all of this extra weight in the ceiling, and then I have a party with 20 guests standing above it. To an earlier point I think the combination of all of that is more their concern, thousands of punds of extra weight on the structure with the drywall and then an event that adds potentially a few thousand pounds of extra weight. At that point there could theoretically be an additional 4-5k pounds on top of the standard weight of the furniture flooring, etc.

The house has engineered joists with an enginnered beam running the length of the span.

1/4" drywall performs virtually-identically to 5/8" drywall, as long as Green Glue is used with it. I would not worry about a performance drop from choosing a thinner drywall. But if you are worried, you might consider using an extra tube (meaning 3 tubes instead of 2 tubes) of Green Glue per 4x8 sheet.

So what the builder and engineer are saying is that if you have a big party of 20 or so guests ( roughly same weight as DD ) and they happen to be gathered in the rooms above, that the floor will collapse ? :eek: Yeh, right. :rolleyes:
Bill


I don't think anyone has said that. The issue is the joists (I don't know the type, the spacing or any other info on them, so I will use my own as an example) are engineered to have a certain structural tolerence. Mine were engineered based on a 10psf dead load and 40psf live load tolerence (which I believe is standard building practice). This tolerence determines the maximum unsupported span based on the OC spacing and the L/360 deflection rating of the joist (L/360 is minimum by Code, L/480 is recommended for a stiffer floor system and will reduce the span size). Using DD on the ceiling apparently exceeds the 10psf dead load limit when flooring, subflooring and walls above this room are also factored in (dead load is empty finished room above, and finished ceiling below) based on the span size. This doesn't mean the ceiling will come crashing down, it just means that the dead load now exceeds it recommended tolerence, which in turn means if there were 20 people and a lot of heavy furniture above this room, and it exceeded the 40psf live load, things start to get dicey. Will the ceiling come crashing down even if the 40psf live load is exceeded? Probably not, BUT, it is now exceeding the RECOMMENDED engineering tolerence. The 10psf dead load limit is just a safety precaution to help ensure the 40psf live load is never exceeded for this particular span size. This is not a bogus excuse or poor engineering, this is the engineer and builder covering their own arses. Oops, I meant to say looking out for the homeowner's safety ;)

I don't know if I want to fully agree with the statement that 1/4" drywall performs virtually identical to 5/8". I didn't see any test results on the GG site that included 1/4" so I have no basis to either agree or disagree.
But I am in agreement that applying GG between the 2 layers of 1/4" will certainly elevate it's performance. The reason I'm reluctant to agree is that they say over and over again that mass is important, which is why in most cases they recommend using drywall over celotex/Soundboard because drywall has more mass. From a mass standpoint compared to 2x 1/4", 2 x5/8" wins hands down. If I remember correctly from a posting by Brian Ravannas, he said that increasing the mass lowered the resonant point of the ceiling wall system, thereby increasing it's performance at lower frequencies. STC ratings apparently don't cover the lower frequencies where subwoofers lurk and where increasing mass has benefits. Hope I said that right; that's what I got out of it, anyway.

Anyway, one thing we're not sure of it the OP's objective or goal for the room. Why did he want to go with 2 x5/8" drywall ? Sound isolation ? Or was he just doing it because that's what is used a lot around here. No offense - just don't know what your design goals are. Not everyone cares or wants to go through the expense of containing the sound of a HT rig from spreading to the rest of the house.


Bill

Anyway, one thing we're not sure of it the OP's objective or goal for the room. Why did he want to go with 2 x5/8" drywall ? Sound isolation ? Or was he just doing it because that's what is used a lot around here. No offense - just don't know what your design goals are. Not everyone cares or wants to go through the expense of containing the sound of a HT rig from spreading to the rest of the house.


Bill

Good point, let me clarify my intentions. The HT room is directly below the main great room of the house. Like many on here I am looking for a way to be able to enjoy my HT to it's fullest without having to listen to the constant complaining from the wife.

The reason for initially planning on 2x 5/8" was due to the research I had done here, it seems like the best reasonably priced solution. Unfortunately given these new circumstances I am now looking for the 'next best thing'. From what I can tell that is either to give QuietRock a try or move to a thinner drywall combination. Given that it does not seem like many folks on here have tried QuietRock I still have not gotten a good picture of it's usefulness. I am gathering that going with 1/2" or even 3/8" drywall with GreenGlue is probably still a feasible alternative that will provide some damping. But if there are other options I am open to hearing them.

I'd take stock of what your construction is and look up code or ask the code office for the load bearing rating in lbs/sq ft.

I googled for 10 seconds and found a few comments about 40lbs/sq foot being the standard for residential floor/ceiling assemblies. double 1/2" drywall should weigh in at just over 3 lbs/sq, and 2 lbs/sq for the floor, leaving a whole lot. The ceiling above my office is rated for 100lbs/sq foot and its hardly that stiff.

One way or another, if you're that close to a weight limit ... i guess i'd be fairly concerned. If safety is an issue with a second layer of drywall, you might just consider no ceiling, or taking the money away from gg/drywall and putting it towards more joists. Or seperate ceiling joists for the room below, perhaps. If one more layer of drywall puts you in the danger zone, i'd focus on safety and not sound.

WRT gg, using double 1/2" or 1/2" + 3/8" or 1/2" + 1/4" to conserve weight will have (as less weight always will) an adverse effect on low-freq isolation (due to less weight), but if the ceiling is not decoupled (no RC or RSIC), the flexibility of these thinner materials has some advantages, and you could certainly still attain a good ceiling.

But safety first, and i'd call the lcoal building inspector/code guy.

Check out this thread for an alternative

http://www.avsforum.com/avs-vb/showthread.php?t=818951&highlight=green+tape

you might be able to get away with a single layer of 5/8.

Good point, let me clarify my intentions. The HT room is directly below the main great room of the house. Like many on here I am looking for a way to be able to enjoy my HT to it's fullest without having to listen to the constant complaining from the wife.

The reason for initially planning on 2x 5/8" was due to the research I had done here, it seems like the best reasonably priced solution. Unfortunately given these new circumstances I am now looking for the 'next best thing'. From what I can tell that is either to give QuietRock a try or move to a thinner drywall combination. Given that it does not seem like many folks on here have tried QuietRock I still have not gotten a good picture of it's usefulness. I am gathering that going with 1/2" or even 3/8" drywall with GreenGlue is probably still a feasible alternative that will provide some damping. But if there are other options I am open to hearing them.

Know what you mean. I deal with that all the time. I swear sometimes my wife could hear a mouse scamper across the street a block away ! :rolleyes:
Her hearing threshold and mine differ greatly, so she is always saying turn it down.
So I have the same design goal as you. I feel your pain, dude ! ;) Trying to isolate the sound in my HT in the basement from the rest of the house, but there is only so much I can do for the price. Don't know how much leakage I'll get because of cold air return in the HT. Using Hat channel, RSIC clips, DD 5/8", and GG in the ceiling with lots of insulation. We'll see how that goes. Couldn't decouple everything from the floor above, so some of effort in the ceiling may go for naught.

Bill

I don't know if I want to fully agree with the statement that 1/4" drywall performs virtually identical to 5/8". I didn't see any test results on the GG site that included 1/4" so I have no basis to either agree or disagree.I based my statement on the generality that more mass is better, but Green Glue outperforms mass by many times. I was only considering the mass difference. I had not remembered that thinner drywall is floppier, and that this can be a problem since the sheets need to press together tightly in order for the Green Glue to be effective.
google.com/search?q=site%3Agreengluecompany.com+%221%2F4%22 (http://www.google.com/search?q=site%3Agreengluecompany.com+%221%2F4%22)
http://www.greengluecompany.com/usingGreenGlue.php

Some time ago, if I recall correctly, Ted White told me over the phone that the first layer of drywall on a (vertical) wall should be at least 1/2", because of the floppiness of 1/4" and even 3/8". Thinking about this further, for this ceiling I think I would check with the contractor if the weight of 1/2" for the first layer and 3/8" for the second layer would fall within the weight limit.


The reason I'm reluctant to agree is that they say over and over again that mass is important, which is why in most cases they recommend using drywall over celotex/Soundboard because drywall has more mass.In that case, the mass is free (or better than free, since drywall is actually cheaper). More mass certainly is better -- it is just not very much better (in my opinion as an observer with minimal actual experience). If the extra mass were free, I would take it.


STC ratings apparently don't cover the lower frequencies where subwoofers lurkThat is true. It ignores everything below 125 Hz.
google.com/search?q=site%3Agreengluecompany.com+125+hz (http://www.google.com/search?q=site%3Agreengluecompany.com+125+hz)

The STC rating system has limited usefulness.