Steel Stud and RC framing question..

I just got through re-reading all the forums' posts, stickies and the entire USG handbook, and I am a bit confused about several wall and ceiling framing proceedures. Please excuse my perhaps overly novice questions, but I would appreciate any advice from those who have already dealt with these issues during their studio design and construction projects.... I will soon begin the renovation and interior reconstruction of a 1500 sq. ft. former demo studio is located on the second floor of a 4 floor downtown building here in Montreal. I have atttached rough floorplans of the current layout, and a draft of our proposed layout. This new facility will have a digital multitrack recording studio as well as an AVID video edting room, both with 5.1 and stereo capability. We have determined through comprehensive testing that the existing wood stud single frame walls and single leaf gyprock ceilings in the CR, ISO and Live Room areas do not achive our desired level of TL and STC. Since the current ceiling (9' 4" high) is just a single layer of 1/2" sheetrock screwed directly into the 16" oc wood floor joists above (uninsulated), and the existing partition walls were poorly sealed and had the wrong density of insulation and low quality gyprock, I assume we must will rip that all down!. Since floating the floors would be beyond our budget, I suspect that we will at least need to build new double frame interior walls and suspend new twin layer gyprock ceilings on RC for these three areas. I plan to replace that existing ceiling by first insulating the cavities with a combination of Roxul and OC 703, then attaching a few 2"X8" and 2X10" wood studs to the existing joists to create a 12 degree slope. I would then somehow secure the insulation into the cavities, and add RC stips upon which I would secure 2 layers of 5/8" Type X gyprock. The current proposed wall construction method would utilize two adjacent steel frames, each using 3-3/8" steel studs of gauge 26 steel, each cavity filled with 3" Roxul Safe&Sound, and a 2" airspace in-between the two steel frames. As per this forum's suggestions we intend to attach 2 layers of 1/2" type X gyprock on 1 side of the interior frame, and 2 layers of 5/8" type X gyprock on 1 side of the exterior frame. My questions are as follows.... 1) Since the steel studs require steel tracks be installed on both floor and ceiling to hold tem in place, should I first rebuild the ceiling as indicated above and then attach the steel studs' ceiling tracks to the underside of the new RC hung gyprock ceiling??? Is there any reasonable way to avoid the new walls and ceiling being coupled as such?? 2) How should I best secure the insulation in the existing ceiling joist cavities without creating a third mass up there??? 3) There are currently functional HVAC ducts hidden by a simple T bar and acoustical tile suspended ceiling (the former studio had added 4" of OC Pink thermal fibreglass insulation above those tiles) resting 16" below the actual ceiling. If I build the new walls and ceiling, and then wish to reinstall the suspended ceiling to once again hide the HVAC ducts, will this acoustical tile and the 4" of thermal insulation placed atop the acoustic tile create a third mass effect??? 4) Am I going about any of these tasks in the wrong way or is there perhaps any alternative methods or design elements I should consider??? 5) Have I overlooked anything that I must re-examine? Have I made any basic errors in my design or construction concepts??? Thanks in advance for your help, suggestions and advice.... RON CHARLES Montreal [removed]

Some quick comments. The route to get from the control room to the live room seems awkward. Either try to work it so there is a door from the control room to the sound lock of use the idea of double sliding doors for the windows between the live and control rooms. If you do that then you can most likely skip the double doors from the iso room to the back room. You will need to double wall between the live room and the exterior and between the live room and the office. Pay attention to the windows to the outside. if you want the natural light then treat them with an inner window like they were a studio window.

Thanks Innovations!. I agree that the access between the CR and ISO and Live Room via the Soundlock is awkward, and it would certainly be better if there were sliding glass doors between the CR and ISO ( John Sayers also wants me to make that change), but at a local cost of over $1550 USD for 2 new sets of good STC rated sliding doors, it's a bit above my budget capabilities for now. I will search around for used sliders and I will install them if I get lucky and find some at a good price, otherwise I may need to consider that approach in a future upgrade. In terms of the existing Live Room to Exterior single mass wall, this is a solid 12" thick granite wall and absolutely zero noise penetrates or exits, so I will leave that as is. The existing (sealed!) Live Room to Exterior windows are custom designed 11 mil. double pane argon windows of very high STC and as such I will leave those as there are now. I will however follow your superb advice and build a double the wall between the Live Room and Office as you suggest (I certainly overlooked that important zone!) . Thanks so much for your suggestions.... RON

In terms of the existing Live Room to Exterior single mass wall, this is a solid 12" thick granite wall and absolutely zero noise penetrates or exits

That wall has STC of around 52. If you don't have any low frequency noise outside that wall, it will be okay, assuming that you are going to put insulation finish drywall etc on the inside. If not there will be noise problems.

Thanks for the reply AVare, Please pardon my ommision, but I seemingly neglected to correctly detail that granite exterior wall's actual composition when I posted the floorplan and also again when I responded to Innovations' reply!. The existing granite exterior wall actually is already covered on the interior (except the window areas) by an adjacent single 2" x 4" wood stud wall with a 3" mineral fibre filled cavity and 2 layers of standard 1/2" gyprock. While it perhaps could be improved upon (Perhaps by adding a final 3rd layer of 5/8" gyprock?), I do not think it is absolutely necessary in our case. We have tested the current exterior wall with third octave tones, pink noise, and a very loud 6 piece rock band (avg C weighted SPL of 116 db), and have had no noticable leekage through either the wall or windows to the street outside. The other good news for us is that even when a huge truck (or a dreaded deisel garbage crusher) passes the street below, there is fortunately almost no measurable rumble or noise anywhere in the facility. Thanks for your input... Ron Charles

There's some useful technical pdf's on wall construction for fire and acoustic performance here... http://www.gyprock.com.au/technical/technical.asp The 'System Selector" on this site (in the pull down menu under "Design") is also useful for checking your design's STC performance. More useful design pdf's here... (Link had to be cut into 3 sections to avoid horizontal scrolling. Copy and paste each section into your browser address line to make one long link without any spaces)

http://www.boral.com.au/brochures/orders/default.asp?
AUD=contractorBuilder&nodes=IC:Plasterboard&toggle
Item=brochures&menuitem=plasterboard&company=Plasterboard

Thanks DownUnder Dave, I had a peek at the gyprock.au site and I suspect I will be using something similiar to wall model CSR275(b) which may yeild theoretical results of about RW 62, which I think should be suffecient for proper isolation between my CR and adjacent ISO and Live Room areas (although the windows are expected to reduce the actual RW and STC and TL ratings to a measurable degree). Thanks for the great link! My main concearn is that I am still a bit unsure if I first install the new ceiling (on RC or the Resilient Mounts if I can find them in time) and then attach the upper steel stud track to the newly suspended ceiling, or if I can find some other better method of securing the upper steel stud track to the ceiling (in order to reduce the coupling between walls and ceiling). Any thoughts??? Ron Charles

The existing granite exterior wall actually is already covered on the interior (except the window areas) by an adjacent single 2" x 4" wood stud wall with a 3" mineral fibre filled cavity and 2 layers of standard 1/2" gyprock. While it perhaps could be improved upon (Perhaps by adding a final 3rd layer of 5/8" gyprock?), I do not think it is absolutely necessary in our case.

With the additional data, I estimate that the STC is in the low 60s and the worst TL down to 62Hz is around 32 dB. Excellent performance! I guesstimated that number from actual tests performed by the NRC and detailed in their IR-586 report. If you are looking at internal wall construction additional testing data on over 350 wall types is in their IR-761 report. Both are available at their website. No need at all to improve the isolation on that wall.

My main concearn is that I am still a bit unsure if I first install the new ceiling (on RC or the Resilient Mounts if I can find them in time) and then attach the upper steel stud track to the newly suspended ceiling, or if I can find some other better method of securing the upper steel stud track to the ceiling (in order to reduce the coupling between walls and ceiling).

At the top of this forum is a link to the USG drywall installation guide. It is considered the bible for drywall installation. It should answer your query about how, the direction is clearly do the ceiling first. It is also full of useful tips and tricks for doing drywall. I noticed that you are who I posted to about not detailing you location. Now I know you are in Montreal. Enjoy! Andre

Thanks to Andre for another rapid and informative reply! I appreciate the encouragement, and thanks for taking the time to look up these massive pdf documents, which I've been poundering over for a few weeks now. The USG handbook is truely a great resource, and it covers almost every aspect of basic sheetrock consturction one would ever want to know about. I have just re-read pages 76-93 which deal with steel framin and RC & furring, and I have learned plenty of solid information (something I need to know as I have never constructed or designed anything before in my life!). Unfortunately, it just says to "INSERT FLOOR TO CEILING STEEL STUDS BETWEEN RUNNERS, TWISTING THEM...." but does not offer any detail as to how to properly install a steel stud wall's upper track (runner) into the ceiling whilest obtaining full or partial decoupling of these 2 structural elements. I am sure this has been dealt with before by several other studios that have used steel studs, but I am just too inexperienced to fiqure out the proper method myself!. I am really a novice at all of this. I have in fact used a National Research Council of Canada's labratory tested design (WALL 345) as the basis of my proposed interior partion wall concept, although I am hoping to take it two steps further than the NRC got to when testing hundreds of wall design combinations. The superb and in-depth lab analysis online pdf document you mentioned (IRC IR-761 "NRC Gypsum Board Walls-Transmission Loss Data") explains the effects of staggering dual framed wood stud walls, but just does not indicate if there is any improvement that might be gained by either using seperate upper and lower tracks (runners) for each of 2 frames (Page 13 figure 6 indicates that all Steel Frame results were measured using "SINGLE TRACKS AT TOP AND BOTTOM", or by staggering steel studs in similiar walls, such as is shown with examples of double frame staggered wood stud walls such as WALL 290. I'm not at all qualified nor mathematically skilled enough to know for sure, but I am, perhaps incorrectly, theorizing that if I build a design such as WALL 345 of the above NRC document, and then add the 2 extra bonus construction features of seperate frames on seperate tracks and staggering the steel stud locations, perhaps a few extra db of STC and higher TL rating at low frequencies may result. Am I totally off target here, or would one or both of these added factors help to further improve the walls' real world isolation??? RON CHARLES Montreal

I just re-read some Kinetics data, and I am beginning to think that they make the products which can solve some of my design issues. I just read about IsoMax resilient mounts (Thanks threads I read by AVare and DownUnder Dave), KWSB Sway brackets, ARS and ICW ceiling supensions, and a few other interesting items. I realize these are top of the line products from a very respected company, but I have a feeling that many of these items are rather expensive for folks like me on a relatively tight budget. Are there more generic sources or alternative products/methods (with fairly similiar results) that I should consider incorporating into my wall and ceiling designs?. Is this just overkill in my case?? Ron Charles

Am I totally off target here, or would one or both of these added factors help to further improve the walls' real world isolation???

You getting into uncharted territory. If you want to start to "custom design" your walls, then I strongly urge you to buy the Insul software progrem. It lets you play with many factors in the design of partitions and see the prdeicted results. The demo program does not let you change the material type, which you may may want to do. It is from Marshall Day Acoustics. I did a quick check with the demo. Adding hte third layer and increaing the spacing by 50% improved the STC by 8 points. The low end TL was still lousy, as all (light weight) walls of this type are.

Travelreview wrote:

I just re-read some Kinetics data,... I realize these are top of the line products from a very respected company, but I have a feeling that many of these items are rather expensive for folks like me on a relatively tight budget. Are there more generic sources or alternative products/methods (with fairly similiar results) that I should consider incorporating into my wall and ceiling designs?. Is this just overkill in my case??

The Isomax is 70% the price of the PAC-International product. The other Kinetics products are considerably more expensive. Is it overkill? Only you can answer that question. You wrote in your first post that the current conditions were unacceptable after considerable testing. Analyse your test results to determine how much isolation is required. Use TL data, NOT STCs! BTW, you are getting into some very unique construction designs. Have you checked the building codes to see if what you are considering can be built? Unbalanced double/triple layers, unbalanced single sided. HAve you considered chase walls?

My main concearn is that I am still a bit unsure if I first install the new ceiling (on RC or the Resilient Mounts if I can find them in time) and then attach the upper steel stud track to the newly suspended ceiling, or if I can find some other better method of securing the upper steel stud track to the ceiling (in order to reduce the coupling between walls and ceiling).

My suggestion would be to install the wall frames first and secure the upper steel stud track to the underside of the joists - fixing them to the ceiling sheetrock doesn't sound very secure to me. I'd also fix timber battens to the sides of the joists and the underside of the floor above, and insulate and sheet those gaps in the same manner as the walls. Then I'd hang the ceiling framework in between the walls. When sheeting, I'd put one layer on the walls all the way to joists, then one layer on the ceiling, then another on the walls and another on the ceiling so the ceiling/wall intersection creates this kind of stepped effect and creates a more difficult path for the sound to follow. If any of the existing walls are in the right position and are soundly constructed, I'd be inclined to strip them back to the framework, add a second wall or resilient mounts, then insulate and sheet them with your preferred materials. It's really easy to rip stuff down, but costs a lot of time and effort to put it back again.

Thanks once again to AVare and DownUnder Dave... I am greatful for your help in trying to set me in the right direction. I realize that I may be stepping into "Unchartered Territory" and perhaps my naive attempts at improving time honored NRC wall designs may be way out of my league, but my inquisitive nature always seems to make me push the envelope a bit more than is needed. Now I have recieved your two opposing opinions in this thread. DownUnder Dave suggests the wall frames should go up first, and Andre has indicated he suspects starting with the ceiling is better, and I think both methods make perfect sense! This is the point of departure for my limited design skills and more limited experience, and thus I have no idea which method would be better suited in my case, so please feel free to jump in with any more thoughts or clarifications on which of these methods I should go with! I have re-checked with a good architect and the city's fire code and building permit departments, and as far as they see it, if I avoid messing with any load bearing walls, and I have used structurally safe methods and materials (the fire dept. inspectors seem to be rather happy with my choice of Roxul and Steel Studs), these specialized designs are generally OK with them. I may nowever need to recheck and modify the fire exit and sprinkler system layouts before submitting the plans they require for the next round of permits. I have another crazy idea, and another question about the ceilings and walls........................ Since the entire existing space has a T bar and acoustic tile drop ceiling, does it make any sense at all to salvage the T bar grid and later reassemble this drop ceiling once I have finished working on the actual ceiling above it, and substitute 2 foot by 4 foot panels of 1" OC 703 in the 2 foot by 4 foot grids where the old crappy acoustic tiles were placed. Perhaps adding vertical hangars of 705 and 703 (or horizontal layers of Roxul) in the approx. 12" high airspace above the T bars where possible????? If so, could I consider using a wide wooven fine wire mesh to cover the OC 703 (I have seen burlap and cotton coverings commonly used for this in other studios' clouds, but the fire inspector may insist I use fire resistant fabrics such as Guilford of Maine, which are too expensive for me). Would such a fine metal mesh (like mosquito netting or patio door screening) be too reflective??? Ron Charles Montreal [removed]

Now I have recieved your two opposing opinions in this thread. DownUnder Dave suggests the wall frames should go up first, and Andre has indicated he suspects starting with the ceiling is better

My mistake. I was thinking of the gypsum installation. Dave is correct. BTW Dave, excellent posts!

I have re-checked with a good architect...

Great!

I have another crazy idea, and another question about the ceilings and walls

Thin light,as in not dense, material like 703 at a distance will not be very flat, or absorbent at low frequencies. If you want to go that route, consider using something like Roxul "Safe n Sound" . The latter is 3" thick 2.5 lb/ft^3 mineral wool. Because of its different market, it is priced at about one fifth of OC 703 by volume! and available at Home Depot etc. If you want to be more confident in the low frequency effect, double the layers of it. This would cost about the same 1" OC 703, if the prices are similar in your area as mine. WARNING! This is getting into uncharted territory again! Underside support is a cost and design factor regardless. Sorry, no ideas on that one. Have you done a modal analysis and RT60 design calculations? The ceiling and length in the main room are 1 to 2. At those low frequencies almost no porous acoustic absorption is effective so the sound will see the hard surfaces regardless of what porous material is put on top. Doing all the ceiling will also make for a very dead environment if you add any more absorption on the walls to control echoes, axial modes etc.

Thanks again Andre!, I have not as of yet done the T60 and modal calculations, but this will be done early this week for sure. The actual ratio of the Live Room ceiling to long wall ratio is currently 1 : 2.36 (at 9' 4" from floor to ceiling joists), under which a T bar acostic tile suspended ceiling now hangs rather low at 7' 10". My only reason for wanting to use OC 703 in the ceilings is that a local supplier is stuck with 20,000 sq ft of 703 FRK and he wants to liquidate as much as I want for well below wholesale cost, and at these prices (about $0.83 CDN/ sq. foot) it seems like I should make some use of it if at all possible. I intend to buy about 38 bails of 3" Roxul Safe & Sound for the steel frame walls from Home Depot here at $0.42 CDN a square foot which is also a reasonable price. Your point about putting too much absorbtion above the Live Room and CR areas is a very good one, and I agree that this most likely will create an overly dead environment! I have already sent EMails and left voicemail for the local reps for Kinetics (Master Ltee) and Auralex (Gotham Audio Canada) and Soundtrap to see if they have any good prices on the Resilient Mounts like the IsoMax, and to see if they will be a good option for my CR ceiling and perhaps my Live Room as well. I also will redo the math to see the necessary quantity need for our anticipated ceiling mass load. My question about using metal mesh instead of fabric for covering OC703 in clouds and other areas still stands, since I know there will be no issues regarding the fire resistance rating of the metal.... Will the metal mesh be too reflective of a covering to use on the underside of a cloud array mounted above my mix position???? The demolishion has begun, and it looks like a tornado ripped through the space. I really love the stress reduction benefits of the sledgehammer work-out I'm getting! - RON CHARLES

Since the entire existing space has a T bar and acoustic tile drop ceiling, does it make any sense at all to salvage the T bar grid and later reassemble this drop ceiling once I have finished working on the actual ceiling above it, and substitute 2 foot by 4 foot panels of 1" OC 703 in the 2 foot by 4 foot grids where the old crappy acoustic tiles were placed. Perhaps adding vertical hangars of 705 and 703 (or horizontal layers of Roxul) in the approx. 12" high airspace above the T bars where possible?????

There seems to be two considerations here - structural and acoustic. Re the structural, if you plan to hang anything off your ceiling, it would be wise to factor this into your resilient mount or resilient channel loading design. Otherwise you may get overloading and lose some flexibility and consequently sound attenuation. Re the acoustic aspect, you may want to run this by a pro. I notice John uses "2 inch Insulco Fibreglass and covered with hemp cloth" in one of his designs - http://www.johnlsayers.com/Pages/Left_Bank.htm. But he also includes other features like slot resonators. If you like to experiment and try out new ideas, a more flexible construction system that lends itself to change might be the go. Perhaps a number of anchor points (possibly resiliently mounted back to the joists..?) from which you can suspend framework or objects. Then you can experiment with prototype structures and/or make changes from time to time.

BTW Dave, excellent posts!

... thanks AVare.

Thanks Dave, I will most certainly take your advice and factor in any potential usage of a suspended ceiling (if I end up going that route) into the loads that affect the resilient mounts or resilient channels for the new ceiling. I will call John Sayers this week to discuss the advantages or disadvantages of T bar grid usage, as well as several other issues that I am unclear about such as using wire mesh instead of fabric on the undersides of the cloud array. I really do appreciate all the great advice from Down Under, Canada and the US in this thread, and I will post any updates and additional queries as I proceed through this strange new territory!. Ron Charles Montral

I have not as of yet done the T60 and modal calculations, but this will be done early this week for sure. The actual ratio of the Live Room ceiling to long wall ratio is currently 1 : 2.36 (at 9' 4" from floor to ceiling joists), under which a T bar acostic tile suspended ceiling now hangs rather low at 7' 10".

Start absorbing (no pun, or insult meant) the acoustics you gave read so far. Sound waves reflect off of hard surfaces. They do not reflect off imaginary lines where the bottoms of the joists are. If the top of joists where the hard surface starts is at 11 feet, then that is what the sound waves will reflect off of. If you put porous absorption below that, whether right against the hard surface, against the bottom of the joists, or 16 inches below the bottom of joists in a suspended ceiling frame, the sound will reflect off the hard surface, not the absorber!

My only reason for wanting to use OC 703 in the ceilings is that a local supplier is stuck with 20,000 sq ft of 703 FRK and he wants to liquidate as much as I want for well below wholesale cost, and at these prices (about $0.83 CDN/ sq. foot) it seems like I should make some use of it if at all possible. I intend to buy about 38 bails of 3" Roxul Safe & Sound for the steel frame walls from Home Depot here at $0.42 CDN a square foot which is also a reasonable price.

Start studying what was written to you and what you didn't write! 1"thin light material has irregular low frequency absorption. Alternative is the safe n sound at about one fifth the price. You wrote nothing about FRK. FRK is actually bad in this application. Ignoring the FRK part, at $0.83 you would have to buy 3 layers ($2.49) to get equivalent to one layer of safe n sound at $0.42. Or if you double the safe n sound you are paying $0.84. The 703 costs 3 to 6 times as much per square foot! You more than pay for what you called top of the line with RSIC and ISOMAX clips with the money you would "save" by not using the specially priced 703.

Hi Andre, Thanks for the great advice! You have made a good point about the economics of Roxul vs. OC rigid. I was planning to attempt a removal of the backing material from the FRK to make it regular 703, thus I didn't previously mention the OC was actually 703 FRK. I will however use Roxul Safe N Sound for most zones as it is a good product at a very reasonable price and is easily available from many local retailers. I understand your point about my not including the foot or so of space above the overhead floor joists in my ceiling height calculations, but I however intend to insulate and seal up those cavities, either with a RC hung or ISOMAX hung dual leaf ceiling of gyprock attached below that joist height, so in that case I believe that my previously posted ceiling calculations are still correct at about 9' 4" minus a few inches of gyprock and mounts or RC. I am beginning to suspect that we have both misunderstood which "Main Room" we were each referring to. Until now I thought you meant the Live Room, but I now suspect you were talking about the control room, which given the ceiling height of 9' or so after installation of a new ceiling at the bottom of the overhead joists, would have been at the ratio of 1 : 2.1 to the max. length of the CR. This actually has been addressed since posting my original draft floorplans by me adding extra length and width to the CR dimensions, unfortunately at the expense of a narrower ISO area. I have also reluctantly added CR to ISO double sliding glass doors as per the strong suggestion of John Sayers and many others. I have attached a revised draft floorplan, slighly off scale, which I will fully re-draft and post in a day or two with more accurate detail and scale. Hope that clarifies some of the misunderstandings, but let me know if I am still wrong, as is often the case!. RON CHARLES

Oops, I finally now see what your were saying about 1:2 ratio in the Live Room, You were in fact correctly explaining that if the exisiting Live Room height is 11' to the floorboards, then 11' is at a ratio of 1:2 to a 22' room width!. I will however still drop that ceiling to 9' or so using the same methods I intend to implement in the CR (RC or Isomax), thus the ratio becomes a more reasonable number like 1 : 2.4 in the live room. I suspect that is acceptable, but please let me know if not. I also just remembered that these golden ratios do not apply in rooms with splayed walls, so my rambling discussion about the changes I have made in the CR dimensions was foolish of me to even bring up in that context. Sorry for the misunderstanding about which room you were referring to, I was a bit distracted and I apologize for my error. - RON CHARLES

Sorry for the misunderstanding about which room you were referring to, I was a bit distracted and I apologize for my error.

Not a problem. The misunderstandings to regret are the ones discovered after construction! :lol:

...thus the ratio becomes a more reasonable number like 1 : 2.4 in the live room. I suspect that is acceptable, but please let me know if not. I also just remembered that these golden ratios do not apply in rooms with splayed walls

That is much better. Remeber when discussing golden ratios etc three assumptions made in the theory 1 All surfaces are perfectly reflective 2 The is perfectly symmetrical 3 There is nothing in the room to reflect/absorb/diffuse sound. So if your room is made of 6" glass surfaces with perfect symmetry and nothing like equipment/furniture/people in it, place great importance on the ratios for best sound performance. As has been written several times, good room ratios at these studio volumes is more to avoid problems as opposed maximizing performance. For a an depth discussion of room ratios see the BBC RD 1993-08 "Optimum room Ratios..."

Thanks Andre for the superb link to the BBC data on room ratios, it was quite enlightening!. I am still trying to source the IsoMax clips from Kinetics to determine of I will use them for the ceiling insted of RC. Irregardless of whether I go with IsoMax and furring channels or just regular RC to attach the double layer sheetrock ceiling to be hung down from the overhead floor joists, I need to place my sheetrock order in a day or two to get it to the site on time. My 4 questions now are...... Should I order the largest size panels (4' x 12') to minimize the quantity of seams that I need to caulk and mud/tape??? Would you suggest the 2 layers of sheetrock I order for the ceiling be the same thickness or different thicknesses (2 x 1/2" or 2 x 5/8" or 1 x 1/2" plus 1 x 5/8")??? I know this next question has been covered to some extent in the forum threads and the USG data, but I am still a bit confused.... When attaching the lower layer of sheetrock to the upper RC or IsoMax/Furring affixed sheetrock layer, what is the suggested method of attachment in terms of the orientation of the sheetrock itself (perpendicular to the first layer?) as well as the recommended quantity and placement and type of screws??? Is using type X fire-resistant sheetrock for this application going to add or subtract TL rates versus using standard sheetrock?? Ron Charles

Ron, got your PM - if these four are your main questions, I'll see what I can do - 1 - Large panels' only drawback is HURTING your back - other than that, use them wherever possible. 2 - Current wisdom from several sources suggests that differing thickness (other than adding a thinner sandwich between two full thickness layers) isn't worth the confusion of grabbing the wrong thickness boards for the wrong layers, so sticking with 5/8" board in 12' lengths is the most practical. 3 - I stick with just sheet rock rather than punky, flimsy materials that may cause fastener problems and blowouts, with dubious or no improvement in the isolation. Fasteners - for sub layers, use half the recommended schedule - if the full schedule calls for 8" OC around edges and 12" in the field, then sub layers should be at 16" OC around edges and 24" in the field. The top layer would get the FULL schedule, making sure that each layer's screws are long enough to penetrate by at least 3/8" for steel, and 3/4" or better into wood framing. Always put subsequent layers at 90 degrees to each other - also, for walls it looks better to have the top layer running horizontal, because of less seams showing. So if doing two layers, the first would go vertical and the last horizontal. For a three layer leaf, go horizontal/vertical/horizontal. Only the top layer of this three layer leaf would get full schedule fasteners. Screw types - USG calls the ones for wood studs Type W, and the ones for going into either RC or steel studs, Type S - some of the ones you find at Home Depot just say "for wood", or "for steel studs" - just remember it's the framing that determines the type of screw; you need finer threads for steel, coarser for wood. 4 - Type X rock is roughly 1/8 pound lighter per sq ft than standard rock in 5/8" panels, so would lose a dB or two compared to standard. However, for commercial property you might be better off using the X just to keep the bureaucrats happy. Let me know if I didn't cover everything... Steve

Thanks Steve for the words of wisdom and straight forward advice, it really clears a few things up for me! I realize you were warning me against using one of the materials in my plan, but I am unclear as to which specific items you were referring to when you wrote.... "stick with just sheet rock rather than punky, flimsy materials that may cause fastener problems and blowouts, with dubious or no improvement in the isolation." Is it the Kinetics IsoMax or Gyprock brand resilient mounts you are cautioning me about??? Thanks a Million, Ron Charles Montreal