Questions about using Steel Studs and Roxul for CR walls...

[Travelreview]

A quick couple of questions for those more experienced than myself in studio design and construction techniques.

After much research, and some help from Nightfly and others on this forum, I have begun designing a new 4450 sq ft. studio here in Montreal. As a novice, am I sure to make several errors, so before I go further I could use a bit of help and advice about our contractors' preference to use steel studs for all our CR wall framing.

Nightfly has recently posted a superb link to the NRC data for TL and STC rates of gyprock walls with over 370 variations of material usage. The address of that site is http://irc.nrc-cnrc.gc.ca/fulltext/ir761/ir761.pdf . While it is a good starting point, they have not included data on the exact wall construction I am debating about using.

In our case, we feel the best affordable combination of superb low freq. TL and overall high STC rating are seemingly found on pages 350 (dual framed wood studs) and page 361 or 363 (dual framed steel studs). Our contractor seems to prefer steel and says it will cut the framing time in half.

My questions are.....

Since local pricing of steel studs (depending on the gauge) is not much more expensive than wood, and installation of steel framing seemingly takes half the time, are there any disadvantages or pitfalls to using steel studs for CR construction that we should be aware of??? (Note: None of our walls will be load bearing as the ceilings will be suspended!).

Some of the best rated walls the NRC has tested use 40mm 25 gauge steel studs at 610mm oc. Would this steel stud spec really be robust enough to safely hold 2 layers of 5/8" gyprock or 1/2" gyprock per frame? If we instead use heavy gauge thicker steel studs like 90mm 25 or even 20 gauge, why does the NRC rates for TL and STC ratings tend to decrease ???

Another question is about the actual stud placement. None of the NRC data shows examples of staggared steel stud frame construction. Would staggaring the steel studs be advantageous (as is the case with wood studs) or would it not be suggested?, Why?

Next, the NRC data on page 361 shows the usage of 40mm mineral fibre with a surface density of 2.2 kilograms per square meter. We hope to use Roxul Safe & Sound ( http://rw-misc.inforce.dk/graphics/RX-N ... s_tech.pdf ), which lists it's density at 2.5 pounds per square foot. Would using this somewhat more dense Safe & Sound be acceptable?

Finally, how would we calculate the final TL and STC ratings if we were to base or walls on the wall design on page 361, but substitute 90mm steel studs and 90mm of Roxul Safe and Sound, and used 2 layers of 1/2" drywall as 1 mass and 2 layers of 5/8" drywall as the other mass? Should we add a wider unfilled air cavity if we have the space to do so?



Ron Charles
Travelreview@Hotmail.com

[z60611]

(I've never built a soundproof wall)

There are lots of links in the sticky here
http://www.johnlsayers.com/phpBB2/viewt ... 87ef52f04a

http://www.usg.com/Design_Solutions/2_3 ... onperf.asp
Talks about Thermafiber, which is rockwool like Safe n Sound (i.e. comparing density might be ok), and says "The best overall acoustic performance was achieved with a mineral-fiber blanket in the 2.5 to 3.0 Ib/cu.ft. density range."

Steel is much easer to carry and keep straight (you can store it months before you actually build). If you're planing on screwing things inside the room (cabinets, shelves, etc) you have to plan ahead, or replace one layer of gypsum/drywall with plywood. There is a concern about rattles, worst case you'd have to remove the walls after they were built, but most who have built with steel say that's poppycock. I don't know what the current rules are for attaching the steel studs to the top and bottom plates: some have written they screw them top and bottom, and I read somewhere that screwing the top is against building code. Someone also wrote that although the steel has higher STC, it also has a higher resonance -- I haven't looked into that yet.

[Travelreview]

Thanks for your reply Z60611,

The links you have provided are quite good (I read all of them in the previous weeks!), but unfortunately they do not really assist much in answering our questions about the specific usage differences and STC/TL results of double framed steel studded wall systems which the NRC has not included in their testing. As I mentioned, they only use either wood studs, dual 40mm steel, or single 60mm or 90mm steel studs in their tests.

Anyone else know of a calcuation method or a good reliable source for detailed STC and TL data for dual framed steel stud walls, that is more comprehensive than the NRC?

- RON

[AVare]

Forget STC. Look at the attenuation by frequency (TL). The NRC data gives results on those frequencies. If you want LF isolation, then go with large mass, like concrete walls. Look out for flanking paths.


Good Luck!
Andre

[Travelreview]

Thanks for your input Andre, your advice is always appreciated!.

I am, in fact, looking more closely at TL data than at the STC data, but both are thankfully present in the available test results for gyprock wall studies such as the NRC (IRC-IR-761).

My issue is that those tests do not include specs for any dual framed steel stud walls using studs wider than a mere 1 5/8". Perhaps I'm wrong, but I remember reading threads here that suggest such thin studs will not be capable of properly holding that much gyprock mass properly. I am trying to find a good solution using more robust 3 5/8" steel studs, but I cannot find out what I gain or lose by doing this to the closest NRC plan found on page 361 of http://irc.nrc-cnrc.gc.ca/fulltext/ir761/ir761.pdf .

For various reasons, using concrete for our walls is not an option in this case. I do however realize that dual leaf, gyprock covered, 190mm cement block walls with an insulated airspace would certainly have trendous STC (I think it is about 79) and much better TL (especially in frequencies over 125hz).

After reading lots of technical data and acoustics tests results from a variety of established engineering departments and testing agencies, I am starting to suspect that we can achieve substancial STC and TL ratings (good enough for serious isolation between our planned new studio's CR and adjoing live room & ISO) by using the correct sizes and combinations of steel studs, type x gyprock, Roxul Safe & Sound, acoustic sealant, and careful installation.

The question is guess I am trying to ask is.....

Could one of you more engineering oriented forum users out there happen to know, or be kind enough to help me calculate, the estimated TL and STC effectiveness, as well as the resonance, of the attached sample wall construction, which is not currently covered in any of the forum postings or broadcast and construction industry technical papers I have yet found.

Please also feel free to suggest any wall design modifications that may help better isolate my future CR from the planned adjacent live room and iso booths....

Any additional help or advice would be appreciated....

RON
Montreal

[sixtiksix]

Hey man,

I am definitely a novice but I would like to help you with some practical data. Here is a pic of the edge of my live room just using steel studs and two layers of sheetrock on the inside. I plan to cut a hole in this wall this week and put another wall behind it making it exactly like your drawing minus one layer of sheet rock on each side. I am opening a metal studio and need some serious isolation. As you can see the crazy assed exterior wall is made of glass making this even more difficult. I have a pro coming over with some high speed measuring equipment and I can let you know how this design pans out on the actual noise reduction side of things.

[Travelreview]

Thanks for the photo of your walls in progress.

As you noted already, please let me know the end results (in terms of isolation achieved) once you get your second frame up and the wall finished off. I have a very similiar concept in mind!.

Could you also please let me know what size and gauge steel you are using for the studs, and how you intend to construct and support the ceiling for that live room?

Ron Charles
MONTREAL
Travelreview@Hotmail.com

[knightfly]

Ron, check the USG handbook (stickies, download it) - page 77 has a chart of stud size, gauge, and loading - figure a little over 2 PSF per layer of drywall, so the 1 5/8 25 gauge studs will support two layers. However, watch the height limits (also listed on page 77)

Staggering studs in separate frame walls - no empirical data as yet, but all my more experienced cohorts agree that staggering studs should improve TL by probably a couple dB.

You've got the right idea on insulation - having the batts slightly bowed in the stud cavities so that the batts contact the center of the span of the wallboard, gives better damping and improves LF TL a bit, probably around 2-4 dB or so.

With double stud frames, the air gap is generally more important than stud type (although it's hard to argue with success) - the bottom line is that a wall that falls down isn't as soundproof as one that stays put so I"d go with heavier studs and make sure the wall stays put.

Calculation wise, a double framed wall with double 1/2" one side, double 5/8" other side, NOT x type gypsum, using light (under 1 pcf) insulation, and with total air gap of 10", comes out at STC 67, with the TL at 50 hZ still a respectable 35 dB - the m-a-m resonance of this wall is around 39 hZ, so there would be improvement available (in the low end) by adding more mass and/or more air between.

Keep in mind if adding a window to this, though, that the window will likely be your limiting factor

Your comment about careful construction is probably the most important of all... Steve

[Travelreview]

Knighfly Comes to the Rescue, yet Again!!!

Thanks Steve,

I know your really busy these days (perhaps I should start a "Send Knighfly on Badly Needed Vacation" fund), so your input is much appreciated.

I am now downloading the entire USG guide and handbook as per your suggestion.

Let me digest that huge document, and re-read some Alton Everest and John Sayers texts, and I'll post a few more specific questions when needed.

I suspect construction will start once permits are issued on Sept. 15, so I have got less than 2 months to get cracking on the design and sourcing issues. I'm calling John Sayers again on Monday, so I will post his suggested design alterations on another new thread the design forum once he is finished.

Thanks a Billion for your help, and I know many of us novices out there would still be completely lost without your wisdom and practical advice...

Ron Charles
MONTREAL
Travelreview@Hotmail.com