air gap or more insulation?

plus6vu wrote:

I am thinking of using channel between the OSB and the gypsum, but I don't know if I have the funding or the time to do that.

Do not. It is at best of no value and probably will maked the isolation worse. Andre

plus6vu wrote:

Rod, You are truly a blessing. Thanks for going to so much trouble to look this up. Not only would I have not even thought about density inconsistencies, but I would not have even thought to ask. Like most folks, I suppose, I figured that since cellulose was so popular, then it must be fine to use. Insulation is insulation right? Well - apparently not. Thanks again.

I do agree 100% that Rod is a blessing and a gentle person which I do respect a lot. But still the question isn't answered about the possible significance and effect on TL of these possible inconsistencies, which calls for much more study of the (existing) IRC-IC documents (including earlier and later ones than IR-761).

Do not. It is at best of no value and probably will maked the isolation worse.

Thanks for chiming in, Andre. That will save me that mistake. :mrgreen: I will take your word on that, but I am curious as to why. I must have misunderstood something down the line. Does the air between the OSB and Gypsum make that the gypsum an additional leaf? I thought that I had seen where people use it between layers of gypsum. Why would it be different since I used OSB :?

But still the question isn't answered about the possible significance and effect on TL of these possible inconsistencies, which calls for much more study of the (existing) IRC-IC documents (including earlier and later ones than IR-761).

Eric, I'm a little curious myself, but I do not have the information or expertise to make those conclusions. I'm just going to have to accept whatever you guys figure out. The cellulose would be a lot easier and less expensive, but I'm not using it unless I find out from one of you that it's okay. I was hoping to use it in the ceiling as well. Fortunately, I'm at least a week from having to commit on that. I've got wire to pull and a 3rd leaf to tear out yet. Many, many thanks guys! Scott

plus6vu wrote:

I will take your word on that, but I am curious as to why. I must have misunderstood something down the line. Does the air between the OSB and Gypsum make that the gypsum an additional leaf? I thought that I had seen where people use it between layers of gypsum. Why would it be different since I used

Welcome to the study of acoustics, where (the absence of) aspirin is not an option. You are creating a triple leaf. You have seen dozens, if not hundreds of examples of people doing just that, and getting abysmal results, and people tearing down what they just built to make it right. This example is not exactly your situation, but pdf page 72 in NRC IRC IR 811 includes two walls (okay, ceilings, but those are just walls turned on their side acoustically) with the only difference being location RC, and a 17 point difference in STC. Andre edit: Corrected formatting code.

Nice discussion. On the installation side of things, we have found that many blown-in cellulose installers presume that a greater density will be needed if you mention the word "acoustic." This seems to be such a common perspective that I have often wondered if this perspective may be in a training manual they use. Additionally, cellulose can settle, changing the density, and perhaps becoming more conductive. Lastly, in a retrofit application, getting the right density is sometimes impossible considering there are hidden pipes, wires and other obstacles that impede the blowing of the insulation. I would note that all of these variables exist for blown in fiberglass as well.

Eric_Desart wrote:

Rod, nowhere they put a direct relationship with this variation in density and the single number ratings. Hence the question remains, how important is this?

Eric, the part of their statement reagarding this that says

"Values should therefore be recognized as rather uncertain; significant changes might occur for the range of densities observed in wall specimens"

is enough to scare me away from recommending their product - and that includes the spray on (although I have a reason to avoid that in addition to the statement above). When you look at their results for the lab tests - there is no significant advantage to using this product over any other product. In fact it doesn't really rate as well as fluffy fiberglass in general - more specifically it is generally a point or so behind the Fluffy....... all other things being equal.... Rod

Eric_Desart wrote:

This wet-sprayed stuff as cavity filling I don't know very well.

Eric, the wet spray we use in higher end homes for insulation - and it is an excellent product for that purpose - however for acoustic isolation it becomes fairly expensive to begin ith (this because the have to cut back the face from the face of stud in a single frame wall because it will cause bridging between the 2 surfaces if it is flush - and in double frame walls it can only be used in the outer most face (spanning the air space will couple the wall frames) and it is virtually impossible to do the inner face with the air space intact. I don't believe there would be any practical way to even think about using it on a staggered stud wall. It's more expensive than either rockwool or fluffy fiberglass - and (given it's limitations) I have never seen any justification in using it on project where isolation was the goal. The blown cellulose (on the other hand) just makes me nervous because of their disclaimer - the terms "significant changes might occur in density" are enough to scare me away........ I studied the differences in otherwise similar walls with measurable changes in density (for walls using fiberglass) and can see (as I pointed out earlier) some fairly significant losses in the lower frequency region's TL as the density increased..... being unable to control the density of the blown make me very uncomfortable. I would hate for the next project to be one that I have to return money to a client (at best - pay for corrections at worse)because I failed to meet the design goals for isolation - I really do love products and assemblies that are very predictable - with a very safe margin of consistent repeatability for the assembly as a whole.......... Sincerely, Rod

plus6vu wrote:

The exterior wall has 3" of insulation already attached and the interior wall will have 6" attached. With that much insulation, there will still be about a 3" air gap. I priced batted insulation and "blow-in" type insulation yesterday. With the price difference, I can buy the blown-in type and completely fill the air gap for about the same price or less and it might be easier and faster to install. I'm just wondering what would be best. Thanks for the help! Scott

A loose blown in insulation is not a good idea in a vertical area. Horizontal areas work best for obvious reasons. Obviously it will give in to gravity...so there is no benefit of any extended kind. That reason alone is enough to negate any suspected gains from a loose blown in insulation. Cellulose, a different thing all together with, is a high quality thermal insulation. As a thermal barrier, it would be the best choice, especially due to the basic design of your build, metal exterior, air basic interior framing/sheetrock. For interior walls, it's not a gain at all, but for the exterior thermal envelope, it is the way to go...cellulose that is.

rod gervais wrote:

Sincerely, Rod

Rod thanks for your reply. And I certainly hope that such technical or acoustic discussions can not jeopardize our relationship. To put this in context for others less familiar with us: I was honored by Rod with an Acknowledgments in his book Home Recording Studio' Build It Like the Pros (among some others):

Eric Desart, even with everything else going on in your life, you found time to help me understand what I needed as I worked my way through this. My best to you and yours.

Just some thoughts: When finishing my stuff in a couple of weeks (I hope), I'll give you (and others) data which as I see it now (therefore I want to check more in-depth) that the results over all data measured by IRC hardly shows any difference. This at least is true until this 50 Hz and up weighting (which is the strictest for our purpose calculated by NRC). In order to calculate this more in-depth I first must integrate ALL measurements I find into Excel, including digitizing their measurements of which no numbers are available but graphs in order to extract these numbers. This will allow me to weigh them with any weighting curve I like, maximum adjusted to our typical music with subwoofers, bass drum and the likes purpose. I also do not want to promote blow-in cellulose, I just want to know how it compares with fibreglass and rockwool. All of this based on data extracted from the NRC reports. And here I will not try to prover anything, but just to know And I find the existing or planned filling will do a good job. But if someone believes he can handel this material with ease (addition holes to be drilled and closed afterwards in an acoustic and estethic sound manner), even when he as DIYER doesn't count some costs, it's worth checking. People decide their priorities based on whatever arguments, not me. In fact this is mainly a thermal material, as so often with acoustic side possibilities. While there are clear analogies between The properties needed for thermal and absorbing materials (both opencell) thermal insulation is at least as critical in function of gasflow (convection). Leaks in thermal insulation are more important, than leaks in acoustic absorption material, where the insulation itself are the masses en the absorption a damper. Hence if this (open) material is suitable for thermal insulation, it almost certain works for acoustic stuff in walls where inaccuracies are less dominant. That whit such a blow-in procedure tolerances can be much larger I agree, fact is that it still doesn't mean any significant (as an average) effect on TL. If blown-in cellulose works for thermal insulation (with normal densities), it should as well work for acoustics. Hence the question is: Since this stuff is mainly used for thermal insulation, is it a well know and documented fact that you can't trust cellulose in vertical applications or not. I can't believe, with the enormous importance of possible failure of such applications (thermal market is HUGE) that no cases should have been documented. And for me there is no reason to assume that if it doesn't fail for thermal applications, it still could fail for acoustic applications, because in terms of impact on TL much more can be accepted than for thermal purposes. @at xSpace

Cellulose, a different thing all together with, is a high quality thermal insulation. As a thermal barrier, it would be the best choice, especially due to the basic design of your build, metal exterior, air basic interior framing/sheetrock.

I don't understand: Since you're against vertical blown-in applications, are these than horizontal applications, or boards, hence not blow-in? I appreciate an exact substantiated answer. This cellulose stuff is used a lot. A bad product disappears from the market. Even the competition will help accomplishing that if valid arguments exist. What I'm searching for are not assumptions, i don't want to promote anything, but just look for an objective comparison and the impact of assumed or real imperfections on TL or Thermal insulation. Not fun exceptions, but as a common or often to be expected problem typically caused by the properties of the material or mounting method. The quote that Rod entered here from IR 761 can sound scary, but for me IRC only told related in function of their gasflow resistance tests. Nowhere they made the link towards the effect on their TL measurements. In another later report IRC makes clear that the impact of density versus thickness is heavily in favor of higher thickness with much less impact assignable to density. But when I make such things it will be complete (in as far possible) that one can discuss a statistical oversight rather than isolated sentences and individual measurements.

Eric, I certainly hope that though I mentioned Rod by name, I thought that I was inclusive of everyone that has helped me here on the forum. You, John, Andre and others have also taken a lot of time to answer various questions much more thoroughly than I could have asked for. I hope to be moving forward on the insulation part of this building project in the next couple of weeks, so I am very interested in your findings. Hopefully I will have the knowledge to understand them. :mrgreen: The reason I would like to use the cellulose is simply cost and installation ease. The wall, as in the diagram, has nothing behind the insulation to hold the batts next to the inner wall (OSB/gypsum sheeting) without my fashioning some sort of wire support. Since the wall and ceiling framing are already in place, putting wire or other support from the back is a problem. It is one that I can deal with if necessary, but it is still a problem. It would be easier to sheet several feet starting at the bottom, blow in the cellulose, sheet several more feet, blow in more, etc. That is really not very difficult at all. Many thanks for everyone's contribution to helping me figure this out. Scott

Scott, Can you give me a link to the blow-in stuff you're referring to? I mean a good link with technical data. Not a link with just a picture of some bag. From the acoustical point of view, I think my belly was right, and we are more busy with bean counting. Hence valid counter arguments must be found elsewhere, meaning in the behavior of this stuff in function of time and the possible or alleged effect on TL. It will take me couple of weeks to do this right (from the acoustical point of view, the technical point I need help), but I'm rather convinced that this will roughly confirm my belly. I don't want to promote this stuff. Basically I don't mind a bit what people use. I just like substantiated objective answers. I even can't imagine that it's easier for you to drill and close such holes with the blow-in procedure. But that's up to you to decide.

Seems like you made your mind up prior to asking it in the forum. Good luck with the rest of the build. lil

lilith_envy wrote:

Seems like you made your mind up prior to asking it in the forum.

I did not had that impression. Scott is just looking for a cheap solution. And for me and a lot of others it remains a dry and valid question: "blow-in cellulose is used a lot, sometimes you even have little choice (walls already mounted). Is it a valid and safe alternative or not? Should an organization as NRC-IRC even bother to measure and integrate it in extensive studies if they shouldn't trust such application from a building-technical point of view?" The NRC still is "Institute of Research in Construction - National Research Council Canada", not just an acoustic lab. EDIT: Here a link which further links to other documents. http://en.wikipedia.org/wiki/Cellulose_insulation By reading more from the building physics side of this stuff, I indeed get the impression that it calls for experience to handle (blown-in) this stuff, that you likely need a density around 3.5 to 4 pcf (which isn't used in the NCR regression approach) in order to prevent this compression by gravity (or whatever you call it). Summary: @ Rod and xSpace: I start feeling/understanding your resistance and question marks about the use of this blow-in stuff, not mainly for the acoustic measurement results as noted in the NRC reports, but for the building physical risks as you guys probably recognized better than I did. @ Scott: I gladly admit (after more reading) that there seems a point in Rod's and xSpaces arguments, not because of Rod's quote from IR 761 which should be checked with the effect on the measurement data itself (and which I did check partly already), but because of the other arguments they used. Hence: I think I must say: I stand corrected.

Eric_Desart wrote:

And for me and a lot of others it remains a dry and valid question: [I]"blow-in cellulose is used a lot, sometimes you even have little choice (walls already mounted). Is it a valid and safe alternative or not? Should an organization as NRC-IRC even bother to measure it if they shouldn't trust such application from a technical point of view?"

Eric, I don't know about other parts of the world - but here - in new construction - the only time we use a dry blown cellulose insulation is in attics where we block out the exterior soffits to a point beneath the roof sheathing - install a material to assure free air flow from the exterior soffits into the attic and then blow in the insulation to whatever depths is required to meet the design specifications. Housing in the states didn't really start getting insulation in the wall cavities (as a matter of course) until sometimes in the early 60's....... most all of the housing built before then was constructed without insulation (not all - but the vast majority). When everyone started getting real energy conscious in the 70's and were looking to cut heating and cooling costs - one of the places they could do this with some real serious effect was through adding insulation to the existing walls - BUT - the method used had to be basically unobtrusive - and someone came up with the idea of blowing insulation into the wall cavities of otherwise completed assemblies. They would remove individual pieces of siding, drill holes through the building sheathing - fill the cavities with insulation - plug the drill holes - and then they would reinstall the siding. The only flies in this particular ointment was that it was very difficult to finish filling the bays right tight to the underside of the cavities, any obstructions in the cavities could cause voids in the insulation, and (most important in my opinion) they were creating a condition with the now insulated bay with no vapor retardant on the cold face of the wall. I remember one house in particular that I did work on that the studs were rotted off almost 2' above the sill for everywhere but the building corners and the bottom of the stairwell. The house was balloon framed - meaning the studs ran from the sill sitting on the foundation continuous to the plates carrying the rafters. Needless to say - I lost my shirt on that particular project. I’ve included a couple of links for you from a manufacturer of cellulose insulation – Note that they do NOT recommend the use of their dry product in wall assemblies…… only ceilings/floors Maybe because of the problems I mention earlier……… The link includes tested assemblies referring to specific UL numbers – make sure to check the actual UL design sheet because their drawings depict things like double walls insulated with spray – that have an air space in the wall cavity – but when I checked the UL Assemblies they indicate that the entire cavity is filled - so you cannot necessarily trust the graphics in their drawings. http://www.nuwool.com/pdf/STC_Ratings_w ... _sheet.pdf http://www.nuwool.com/Products/Technical/CSISpecs.aspx http://www.nuwool.com/Products/Technical/Technical.aspx Rod

Eric_Desart wrote:

rod gervais wrote:

Sincerely, Rod

Rod thanks for your reply. And I certainly hope that such technical or acoustic discussions can not jeopardize our relationship.

Eric, there is no discussion in the world that could ever jeopardize our relationship......... I am always open to learn - am not nearly foolish enought to think (for even a moment) that I know it all - and am more than willing to admit publically when I find myself to be in error. For teaching me without charging me I should always be grateful to you - our friendship stands on it's own. Thanks, Rod

The wall, as in the diagram, has nothing behind the insulation to hold the batts next to the inner wall (OSB/gypsum sheeting) without my fashioning some sort of wire support. Since the wall and ceiling framing are already in place, putting wire or other support from the back is a problem.

Wouldn't it be easier to just slide in sheets of 703 or something similar? Being semi-rigid, they shouldn't need any support from wire or suchlike. Following your same suggestion: sheet a few feet of wall, then slide in some chunks of 703, into the cavity, then sheet some more. etc. I'm not a builder, so that might be a bad idea for other reasons, but it seems to me that it would be easier, cheaper and just as effective (bot acoustically and thermally) as blowing stuff in. Just a suggestion. - Stuart -

lilith_envy wrote:

Seems like you made your mind up prior to asking it in the forum.

Eric_Desart wrote:

I did not had that impression. Scott is just looking for a cheap solution.

Exactly. I thought that I had come up with a good solution, yes, but it looks like I was wrong. That's why I posed the question before I did anything. I have a habit of finding problems others haven't and thus having to find solutions for them. Actually, Lil, you have the same issue don't you? You're project is very similar. How did you deal with it?

Eric_Desart wrote:

I gladly admit (after more reading) that there seems a point in Rod's and xSpaces arguments, not because of Rod's quote from IR 761 which should be checked with the effect on the measurement data itself (and which I did check partly already), but because of the other arguments they used. Hence: I think I must say: I stand corrected.

It looks like I have a consensus then. :) I'll have to find another solution. and Stuart may have found it for me.

Soundman2020 wrote:

Wouldn't it be easier to just slide in sheets of 703 or something similar? Being semi-rigid, they shouldn't need any support from wire or suchlike. Following your same suggestion: sheet a few feet of wall, then slide in some chunks of 703, into the cavity, then sheet some more. etc.

I have a number of scraps of ductboard around here. I could cut them and wedge them just enough to put pressure on the insulation and hold it next to the OSB. Not being a solid connection and just putting slight pressure on the fluffy, I'm just guessing, but I don't see any flanking issues. Scott

"Actually, Lil, you have the same issue don't you? You're project is very similar. How did you deal with it?" 1) I built inside out, So plasterboard is holding insulation in on the non- accessible side 2) I used 120mm thick rock wool and in the end didn't even need to run twine. It's (At least for now) standing up on it's own and has been for 5 months. I like stu's idea of rigid 703 holding it in place. Can you send a pick of where you are up to, or a SKP. Is the ceiling on yet or will you need to bore a hole to put the cellosue in? Could you hire a small child to attach the twine at the bottom :mrgreen:

as to the question of how to hold up the insulation - either any strapping that could be stapled to the stud face (you could actually make this pretty easily just using 6 or 8 mil poly - cut it 4" wide, bend in 1/2 & staple it to the stud face)...... You could do this easily for both walls as long as your studs stagger...... Rod

Eric, I must admit I may have missed a few words and made a few assumptions, RE: cellulose. http://www.youtube.com/watch?v=UP8v5wfVgtY This is to what I refer when I mentioned blown in cellulose. Since it is known that cellulose is a paper product with a fire retardant agent, it was assumed that to attache it in a vertical plane would require something more then just paper. My bad ;)

lilith wrote:

1) I built inside out, So plasterboard is holding insulation in on the non- accessible side 2) I used 120mm thick rock wool and in the end didn't even need to run twine. It's (At least for now) standing up on it's own and has been for 5 months. I like stu's idea of rigid 703 holding it in place. Can you send a pick of where you are up to, or a SKP. Is the ceiling on yet or will you need to bore a hole to put the cellosue in?

I would have built inside out, but somewhere when I started this project, maybe from the inspector, I don't remember, I got the impression that it wouldn't pass inspection. They like to see the gypsum as a fire barrier to protect the studs. (I don't know, I'm just repeating what I probably misunderstood.) So, I am where I am. :| This room is going to double as my living room - I'm not married, so it works for me. :mrgreen: Notice I said this room is doubling as a living room and not doubling as a studio. There is a difference. The studio design gets priority. But, I am inside the city limits in a residentially zoned area (even though I'm a several miles from town - it's a long story). So, I am limited by residential building codes. That's been a good news/bad news issue. The insulation will stand up just fine, no problem there, it just doesn't maintain good contact with the OSB without something "pushing back". All that is up is the framing, so there's no holes to drill and if there were, covering them would be easy. Netting it in and filling it like in UTube video XSpace linked would still be easy.

rod gervais wrote:

as to the question of how to hold up the insulation - either any strapping that could be stapled to the stud face (you could actually make this pretty easily just using 6 or 8 mil poly - cut it 4" wide, bend in 1/2 & staple it to the stud face)...... Rod

This looks like an easy, workable solution. I've even thought of wrapping twine around the backs of the studs about every 2-3 feet, but it would compress the insulation at those points. The small amount that would be compressed - would that be a problem? Scott

The insulation will stand up just fine, no problem there, it just doesn't maintain good contact with the OSB without something "pushing back".

I'm not sure I understand: Why do you need it to maintain good contact with the OSB? The main purpose of the insulation is to damp the cavity, not to damp the wall surfaces. There's a link to a study somewhere here that discusses the position of insulation inside a wall, and as far as I recall, the conclusion was that it doesn't really matter if you have it touching one leaf, the other leaf, both leaves, or in the middle, not touching either of them. What is important is that you have plenty of it, as thick as possible, and that it fills the entire cavity, top to bottom and left to right. The only issue I recall seeing in that paper was with insulation of very high density that was stuffed in too tight so that it created flanking between the leaves. But apart from that, there was very little effect from the placement within the wall. Is there another reason why you need it to be in firm contact with the OSB?

Soundman2020 wrote:

Why do you need it to maintain good contact with the OSB? The main purpose of the insulation is to damp the cavity, not to damp the wall surfaces. There's a link to a study somewhere here that discusses the position of insulation inside a wall, and as far as I recall, the conclusion was that it doesn't really matter if you have it touching one leaf, the other leaf, both leaves, or in the middle, not touching either of them. Is there another reason why you need it to be in firm contact with the OSB?

>> jumping in the way-back machine<< Three years ago, I had the same problem with another wall and did not discover that it might be a problem until after the fact and had to hope and be creative. I'm trying to prevent the problem this time. Previously Rod said:

Rod wrote:

However, a lack of DAMPING of your wall panels (from medium contact with the insulation) WILL be noticeable.

Again, that was more than 3 years ago here viewtopic.php?f=2&t=6971 Now, if new information has come up that I've missed, or if I mistated my problem then or misunderstood Rod in that post, then Yay for me! If what you're saying is correct, then I'm a very happy person and I can go on about my building. :mrgreen: :mrgreen: I was just under the impression that the insulation was a dampener for the walls as well as the cavity. I'm looking forward to hearing a positive confirmation on what you are saying. Don't misunderstand, I know you are in a better position to tell me than I am to figure it out, but it seems that either new information has been presented in the past 3 years or I have a conflict of opinions. Scott EDIT: OOps! That was Steve, not Rod earlier. My apologies for the confusion.

I brought this same point up at slutz. A guy said check out nrc-ir-766. Insulation at the bottom, at the top, and middle showed no difference in TL. The problem I have with using 766 is.. It's for joist-ceiling assemblies, tested with a tapper. 2nd or 3rd page of summary states.. " Placing insulation/absorption material in cavity shows virtually no help in TL when resilient channel wasn't used." You can have insulation at the top without it touching. or at the bottom without touching. So they didn't really test what we are talking about. I would LOVE to see real data testing the dampening value of "lightly touching." To me it would have to stop the panel from vibrating freely. Now how much????? Who knows. Since you can hold it back or have it lightly touching for the same cost, to me it's a no brainer. I'm having it touch. Thanks in advance.

If panel damping were a goal, you might consider pre-damped drywall, or thoroughly damp the drywall with one of a number of damping materials.