Exterior wall, width limited. What do you think?

[marathon]

Hi, all. I've really appreciated this resource. This is my first question; hope it's a good one, and I hope to offer good input soon.

I'm building a garage with studio in the back; new construction. Studio is based on the one-room design from EQ magazine's Sept 04 issue. Due to local restrictions and the need to fit cars in the garage, I'm unable to do a staggered stud wall, or double wall with air gap. I can do a one-wall design. Three of the walls are exposed to neighbors. I've planned a 5 3/4" thick wall, and probably need to stick close to that width.

What do you think of this plan? Could I do better (cost, materials, STC, etc.)? Is there something stupid here? Am I (or are the neighbors) going to be particularly vulnerable to a certain kind of sound trouble?

Item, Thickness, STC, Mfgr, Model #

Exterior Sheathing: 1/2”, in wall, Celotex, Premium Insulating Sheathing Stud Wall: 3 1/2", 35, 2x4, 16" OC
Insulation: -, 4, Owens Corning, QuietZone [R19 instead? Exterior wall]
Resilient Channel: 1/2”, 3.5, Auralex, RC-8
Sheetrock: 1/2", in wall
Sound Barrier: 1/8”, 27, Auralex, SheetBlok
Wall Board: 5/8”, 18, Quietsolution, QR-530

Total: width 5 3/4", STC 87.5



Thanks a million for any input! - Jeff

[cadesignr]

An STC of 87.5? I don't think so. Where did you get these ratings for this wall? 35 for wood studs...... How do wood studs get an STC rating?

fitZ

[marathon]

An STC of 87.5? :shock: :shock: I don't think so. Where did you get these ratings for this wall? 35 for wood studs...... :? How do wood studs get an STC rating? - fitZ

35 STC is not for the studs, of course; it's for the section of wall construction up to that point. I'll go through my notes to find where I got that element of the total, and list it here. If the overall STC listed looks way out of line to you, do you have an idea of what would be a more sensible assessment, or a more realistic total STC for this design? i.e., do you perhaps have a helpful comment?

I'm not trying to have this handed to me on a silver platter; I'm doing whatever research I can - but I'm a neophyte. Nothing I can do about that other than what I'm doing, which is trying to learn more from whatever resources I can find. And this message board is clearly chock full of knowledge and experience. If you have something instructive to say, I'd really appreciate that, rather than something dismissive. Many thanks.

[knightfly]

Jeff, you can't just add 35 dB and 25 dB and get 60 dB; the decibel is a logarithmic ratio, so you first have to convert to a real ratio, then combine, then re-convert back to decibels. Here's a basic idea of how this works;

http://www.safetyline.wa.gov.au/institu ... l54_05.asp

Also, you can't just add (even doing it the hard way) decible values for each material in a wall and expect to get close to a real STC value. A wall becomes a system, and each component of the system adds or subtracts from the whole in different ways and at different frequencies.

In actuality, the wall you show would likely come in at around 50-53 dB STC, with a mass-air-mass resonance of around 79 hZ, and the Transmission loss at the low end of the audio spectrum would run around 25-27 dB, due to the high resonance.

This can only be improved by wider distance between inner and outer leaves, higher density insulation, and more mass in each leaf.

On top of this, I'm not sure which Celotex product you're referring to but the versions of this I'm familiar with aren't a very high mass material, and should NOT be used alone (or even with other materials) for sound walls -

Here's a page that explains most of this better than I can -

http://www.domesticsoundproofing.co.uk/tloss.htm

I hope this gives you a better idea of how this stuff works... Steve

[cadesignr]

Hello Steve, I have a question regarding the LAST partition illustration, the one with an STC of 63. I wonder if this illustration is based on both plates being on the same surface? If so, I wonder if this STC increases if one is decoupled from the other on a floating floor? I mean, WHEN they tested these, it would seem they would be on the same floor, correct?

Also, let me offer an apology Jeff, if my question seemed condencending or offensive. It wasn't intended that way. I was just .....well, shocked I have never heard of a SINGLE wall with this high of an STC rating, and was sincerely interested in where that came from, as I am familiar with the illustration on the link Steve posted, and your total STC seemed to suggest an error somewhere. I had thought of that illustration, but couldn't remember where it was located to link it, and I am NO expert at this stuff so I didn't have anything constructive to offer either. Sorry.
fitZ

[Michael Lee]

What do you think of this plan? Could I do better (cost, materials, STC, etc.)? Is there something stupid here? Am I (or are the neighbors) going to be particularly vulnerable to a certain kind of sound trouble?

I am drawing the plan for Marathon and guessed at the STC rating for the wall to be 35. I'm probably a little high but I couldn't find a detail showing 1/2" celotex exterior sheathing, stud, then 1/2" interior drywall. We have wall width constraints of 5.75 inches and are looking for the best system for the best price to fit into those dimensions.

I've enclosed the section detail for the entire room. Before continuing with the drafting, we want to be certain we are providing the best isolation at the lowest price.

QuietRock calculations based upon difference between standard sheetrock assembly and QuietRock assembly shown at http://www.quietsolution.com/constructi ... tions.html.

1# Vinyl STC number pulled from http://www.auralex.com/sound_isolation_ ... etblok.asp

Resilient Channel STC number pulled from http://www.auralex.com/sound_isolation_ ... _Table.pdf. They actually show a STC of 7 but I took the modest approach.

Insulation STC number pulled from http://www.saecollege.de/reference_mate ... 0Chart.htm. The chart for resilient channel actually shows a STC of 7. Again, I used the modest approach.

Please let me know if the above information is factually incorrect and if so, please show me where. Anyone with constructive criticism (the type that adds information without just cutting down the design) is greatly appreciated.

Michael Lee
Draftsman

[Michael Lee]

Jeff, you can't just add 35 dB and 25 dB and get 60 dB; the decibel is a logarithmic ratio, so you first have to convert to a real ratio, then combine, then re-convert back to decibels. Here's a basic idea of how this works;

http://www.safetyline.wa.gov.au/institu ... l54_05.asp

Also, you can't just add (even doing it the hard way) decible values for each material in a wall and expect to get close to a real STC value. A wall becomes a system, and each component of the system adds or subtracts from the whole in different ways and at different frequencies.

Accoustics is a learning process for myself also. I appreciate your assistance and will research this further. If you could look at my assembly and let myself or Jeff know what products could be considered to make a significant difference without running up cost, it would be appreciated. The dimension of 5-3/4" is all we have to work with for wall depth. No more.

The reason for the Celotex is that that is an exterior wall and structural sheathing is required. We could use OSB or CDX plywood but from what I've read, the Celotex has better properties for sound dampening then either of the others.

Again, we are in the idea gathering stage so any help is appreciated. I'll study the links you have provided. Again, thank you.

Michael Lee
Draftsman
(and complete accoustical novice)

[Michael Lee]

Lesson learned about STC ratings. I'm gonna drop them. The simple request is based upon this drawing, what can be done to improve the rating without running the cost way up. Any and all suggestions for improvement greatly appreciated.

Michael

[marathon]

Also, let me offer an apology Jeff, if my question seemed condencending or offensive.

Thanks much for saying so, fitZ, even though it's not really necessary. I think I was just eager to see that someone had posted a reply, and I shouldn't have been thin-skinned when it was hinted I might not know what I was talking about. ... because I'm definitely on the steep part of the learning curve.

Steve says the current wall design likely comes in around 50-53 STC. I'm now also looking to see whether I can find documentation discussing what STC rating would make for an acceptable backyard studio. i.e., what STC should I try to achieve in order to not have the cops called if I'm working at 10:30pm? And is that going to be possible with a single 5.75" wall design? The neighbors will be (very rough estimate) 30-40 feet away.

[Michael Lee]

Along with the section plans I think it might help to understand the restrictions placed on the project. We have a 700 SF total requirement and have to include a 2-car garage in the design. See attached sketch. The shape of the studio requires front wall to be 11', back 15', length to be 21' and height to be 8'. All dimensions are in the interior finished requirements.

Michael

[cadesignr]

Hello Jeff and Michael. Say, I have a question regarding the building. Is this a NEW addition to the house? Reason I ask, is you mentioned that the Celotex is required for structural reasons. This must be for shear, correct? From my limited knowledge, Celotex seems like a really weak panel for shear resistance, although I am NO expert. And I'm a little bit confused in the first place. If this is new, has the Building inspection department OK'd Celotex for a shear wall? Or can't you use 1/2" ply as the shear panels on the outside? And if it is existing, wouldn't it already have shear panels on the outside if the interior were unfinished and were required in the first place? Another question. Is the vinyl layers under the plate as a moisture barrier? BTW, from your drawing, it looks as if this is a unattatched freestanding building, correct?
fitZ

[marathon]

fitZ, I can answer the most basic of those questions: :) Yes, this will be new construction, and a freestanding structure. This is why I'm concerned with the STC attainable by a single wall design of such limited width - because whatever gets through those walls is getting to the neighbors. - Jeff

[Michael Lee]

This must be for shear, correct? From my limited knowledge, Celotex seems like a really weak panel for shear resistance, although I am NO

Structural sheathing consists of products like 9/16 OSB, 1/2 plywood, 1/8" thermoply (which I don't like at all), and 1/2" Celotex. They all perform the same basic function of keeping the building from racking. The Celotex breaths a lot better than the other products (perm rating of 20.0 vs 2.0) and considering we are basically sealing off the inside with a vinyl sheet, I think breathing will be important in case of trapped moisture. Plus, I think there will be less vibration transfer than with plywood or OSB (in my less than knowledgeable opinion). Certainly, Celotex is likely structurally weaker than the plywood or OSB but I believe the benefits outweight the deficiencies. All meet code and Celotex has been around a long, long time with no record of structural failures that I am aware of.

The vinyl under the plate was a recommendation on one of the acoustic sites to help isolate the stud. They show it at the top and bottom (yea, I forgot to draw the top). Likely, the building department won't like it and I'll have to change it to foam but I'm willing to give it a try. It's the same vinyl material used on the vertical surfaces.

If you know of any other structural sheathings or other product ideas we could use with better properties, I'm all ears. Just direct me to the nearest hyperlink and off I go...

The structure is a completely new construction, detached garage & studio.

If you need any more information, please let me know.

Michael

[Michael Lee]

One thing I found in my research is that rock wool is a lot denser than FG insulation. Is the rock wool worth the investment in terms of getting any significant return for the dollar?

[PhiloBeddoe]

I am not an authority on any of this stuff but my advice is that you may want to reconsider the Quietrock, or at least how it is being applied here. I'm not sure if you've priced it yet, but it's about $120.00 per 4'x8' sheet so it needs to be considered carefully.

If you read a little more into Quiet Solution's pitch, their argument for purchasing the Quietrock is that it removes the potential of "short-circuiting" a resilient channel system by nailing/screwing directly through the channel into the studs or other failure modes. I believe this is a very valid concern, but you are suggesting the use of both Quietrock and RC which negates the benefit. I don't think any of their proposed wall configurations include RC.

Also, if you look around this forum and others, you'll find some good opinions about mass loaded vinyl. I'd recommend shopping around if you decide to use it.

Best of luck