Drywall on the 'outside portions' of NEW structures? (as per Rick Fitz's STC chart)

[ENIGMACODE]

Hello Rick and Michael

In regard to drywall installation, I've gotten some valuable information in the past from: Rod Gervais,Innovations,Rick,and Frederick.

As Rick illustrated here:
http://home.ucwphilly.rr.com/livesound/rick-combo.jpg <the 'boxed example' would apply to my situation explained here:

Do I understand this to mean that even in regard to 'wood' stud construction, (double wall partitions), where one 'outer' wall is built facing the exterior 'OUTSIDE', and in my case where another 'interior' sub wall is built as part of a 'FREE STANDING' room, that it is better to leave that 'OUTER' wall 'WITHOUT' Drywall installed facing the inside NON-Drywalled side of the 'INNER' wall - so that you have 2 exposed insulated walls facing each other???

As illustrated here:
http://home.ucwphilly.rr.com/livesound/par-combo-1.jpg

And does it really matter in regard to these scenarios?
As illustrated here:
http://home.ucwphilly.rr.com/livesound/par-combo-2.jpg
http://home.ucwphilly.rr.com/livesound/par-combo-3.jpg
http://home.ucwphilly.rr.com/livesound/par-combo-4.jpg
http://home.ucwphilly.rr.com/livesound/par-combo-5.jpg

*Please bear in mind that NONE of this NEW structure is actually fastened to the OLD structure. (I took GREAT pain to isolate the NEW walls with home-made iso brackets as per Rod Gervais's advice)

Thanx again guys ..
Best Regards
Mike Fraticelli
ROCKON@ucwphilly.rr.com

 

[Michael Jones]

No. EC, that would be for interior double walls only.
Like the wall between, say, the live room, and the control room.

The outside, or exterior walls need to follow local building codes.
In my case, what I built for exterior walls is a staggered stud wall, with 1/2" OSB, House wrap, 3/4" rigid insulatiuon (not 703) also called "silver board" in these parts, then a concrete brick facade.

On the inside of that exterior wall the cavity is filled with rockwool, then I have 1/2" drywall, 1/2" OSB, and a final course of 5/8" drywall.

Hope that helps.

 

[Michael Jones]

OK, I looked at your pictures.
In the first picture, what is on the other-side of the insulated wall?
Is that an exterior wall?

In my area, due to the local amendments to the UBC, ALL INTERIOR SIDES OF EXTERIOR WALLS MUST BE SHEETROCKED.

I think I would rather sheath, drywall, ect, the inside of an exterior wall; if for no other reason than heating and cooling effeciency.

Also, what comes into play in my situation is that its a staggered stud wall. (My exterior walls, that is.) Therefore BOTH sets of studs are load bearing. A load bearing wall MUST be sheathed because its a structural element. Drywall is not an approved sheathing componet, but OSB is. So I end up with these MASSIVE wall sections anyway.

Clear as mud?

For YOUR situation; I don't know what to tell you other than check with your local building inspectors.

 

[ENIGMACODE]

Hello Michael

Hello Michael

I think you cleared everything up!

In answer to your question that small wall is the exterior wall. It's approx. 7' x 6'. (It's where a garage door used to be). The construction is T11 on the outside over sheathing and foam over that. It's a NON bearing wall and built according to code. I plan on building an inside sub-wall (as illustrated)

I believe you have answered my question - that double wall chart that Rick posted refers to inside walls (as you pointed out)....here:
http://home.ucwphilly.rr.com/livesound/par-combo-1.jpg

And does it really matter in regard to these scenarios?
As illustrated here:
http://home.ucwphilly.rr.com/livesound/par-combo-2.jpg
http://home.ucwphilly.rr.com/livesound/par-combo-3.jpg
http://home.ucwphilly.rr.com/livesound/par-combo-4.jpg
http://home.ucwphilly.rr.com/livesound/par-combo-5.jpg

*Please bear in mind that NONE of this NEW structure is actually fastened to the OLD structure. (I took GREAT pain to isolate the NEW walls with home-made iso brackets as per Rod Gervais's advice)

*And esthetics (appeareance) is not a concern

Any other other comments?

Best Regards
Mike Fraticelli
ROCKON@ucwphilly.rr.com

 

[Michael Jones]

Any other other comments?

Best Regards
Mike Fraticelli
ROCKON@ucwphilly.rr.com

You've got a GREAT project going on there! Nice looking work so far.
Is there any reason for NOT using RockWool in the wall cavaties?
Other than economics?

 

[ENIGMACODE]

Hello again Michael

Hey Michael

'RockWool' as opposed to just plain R11?

Actually I didn't give it much thought

I'm still early on in the game here to switch over to Rockwool. Can it be stapled in place as you would R11? Advantages?

Hey Mike can you check this out too please?
https://homerecording.com/bbs/showthread.php?t=134159

Best Regards
Mike Fraticelli
ROCKON@ucwphilly.rr.com

 

[Michael Jones]

The idea behind RockWool is that its much more dense than R11 or fiberglass insulation.
Remember, you're trying to add mass and density to the entire wall section, and not just with the sheathing or drywall. Think of the wall section as one cohesive unit.
You'll gain a little in thermal value with RockWool, but that's not the main purpose for using it. (Rockwool's R Value, depending on the density, is R4 per inch; so a typical section of Rockwool would yeild an R16 value.) But more importantly, its density is 4 - 6 lbs/cu.ft. Compare that to fiberglass insulation whose density is 1 - 2 lbs/cu.ft.

The down side of rockwool is that its more expensive, and can be difficult to find. Your typical Home Improvement Center is not going to carry it, and they probably don't even know what it is.
You'll need to find a commercial insulation supplier to get it, and even then, they may have to order it.

 

[fitZ2]

In my area, due to the local amendments to the UBC, ALL INTERIOR SIDES OF EXTERIOR WALLS MUST BE SHEETROCKED.

Isn't this odd. I asked an inspector in my county this question SPECIFICALLY as it contridicts MASS AIR MASS(2 leafs with insulated and sealed airspace) profile. His answer was the same as Michaels, and he added the fact that it would negate the use of FIREBLOCKING if you do NOT sheith the insterior face of EXTERIOR walls. But this creates a conundrum for those who are trying to build stuido following the MASS AIR MASS law.

ANY time there are TWO or more airgaps, such as in the case of Michaels example, this becomes a THREE or more leaf system, which by my understanding, significantly REDUCES the STC of the assembly. With that in mind I asked John Sayers what he does for 3 leaf systems. This was his answer:
The OUTER 3rd leaf MUST be vented. In his only example, he stated that the exterior 3rd leaf was OLD board and batten siding, that was warped, which created venting to prevent the AIRGAP being SEALED. It is this SEALING which makes an AIRGAP to act as a SPRING, which in turn is the force that allows the MASS AIR MASS principle to work. But his answer in regard to sheetrocking the interior face, was not applicable. He simply lined the voids between studs(the rear face of the board/batten sheithing) with 2 layers of sheetrock and caulked all the joints. Which really didn't make sense to me, as it would seem that the sheetrock/board/batten would now become the second leaf Go figure. So I have YET to hear any concrete advice or example of how to overcome this dilema WHEN PERMITS and INSPECTION are part of the process, other than to add more layers of sheetrock to the INTERIOR face of exterior walls, to overcome the negative reaction of 3 leaf assemblys, OR vent the 3rd leaf between studs. This could be as simple as drilling a hole in the exterior leaf. Soooooooooooooooo My conclusion is simple.

It is a no brainer why details of these sort of things are not found on the internet, as the simple explaination is some people building HOME STUDIO type construction do so WITHOUT permits OR their local codes do not require the sheetrock on interior face of exterior walls(which seems ludicrous to me) It is also a no brainer why you won't find details of PROFESSIONAL facility construction as these are probably highly guarded design solutions by architects and studio designers, who by virtue of training, experience and other criteria, do not want their solutions copied. However, the most logical explaination is that the isolation walls of professional facilitys are SELDOM part of an exterior wall assembly. Take a look at studios on the internet. Most of what I have seen, have the controlroom/studios moved to INTERIOR spaces seperated from exterior walls by hallways, offices, bathrooms, workspaces, lounges etc. No wonder, as this level of professional expertise and financial investment, allows space to exploit the correct design criteria to avoid this sort of delima. Not to mention that most professional facilitys, IF confronted with exterior walls as a part of the iso wall assembly, do so with a CONCRETE leaf.

So that about sums up what I understand Mike. But as usual, my disclaimer stands as my defense.
fitZ

 

[knightfly]

Some fire safety links I've recently discovered - be sure to check out ALL the first one - I have the IBC complete on my laptop, which isn't available right now; when it is, I'll try to dig out the applicable parts according to comments on this site -

http://www.firestop.org/

And from our Canadian friends -

http://irc.nrc-cnrc.gc.ca/newsletter/v3no3/fire_stops_e.html

http://irc.nrc-cnrc.gc.ca/fulltext/prac/visi350/visi350.pdf

These and several more valuable links are now available in the REFERENCE section of my forum, here -

http://www.johnlsayers.com/phpBB2/viewtopic.php?t=2125

Enjoy... Steve

 

[Rod Gervais]

So I have YET to hear any concrete advice or example of how to overcome this dilema WHEN PERMITS and INSPECTION are part of the process, other than to add more layers of sheetrock to the INTERIOR face of exterior walls, to overcome the negative reaction of 3 leaf assemblys, OR vent the 3rd leaf between studs. This could be as simple as drilling a hole in the exterior leaf. Soooooooooooooooo My conclusion is simple.

I don't understand the problem here.......

I am not familiar with the codes in your area - however - every code I AM familiar with allows the use of rated tested assemblies.

I can come up with a number of rated tested EXTERIOR wall assemblies using double framed wall assemblies with no sheating on the inner face of the exterior wall. But all of them do have to have the inner face of the wall sheathed - iy's just that the inner face of a double frame wall is the 4th surface - not the 2nd (counting from the outside).

So build it like it's shown (in UL - FM or whatever testing lab your using) and it should be allowed.

Therma fiber is an accepted fireblocking - so utilizing this shouldn't be a problem.

By the way - I don't know of any codes that EXCLUDE the use of rated tested assemblies..........

Michael - what section of the Austin code are you specifically rfering to - I went looking and couldn't find it.

I would be interested in seeing exactly how it's worded.

Rod

 

[knightfly]

Rod, thanks for the definition clarification on double framed walls - I was looking thru about 100 pages of chapter 7 of the IBC looking for just that - do you have an actual section number, so I can bookmark it? Or am I looking in the wrong place?

BTW, apparently several types of insulation are considered acceptable for fire blocking, mostly rock or slag wool? From what I've found, those two are more fire resistant and heat resistant than glass wool.

Man, I could find several things more pleasant than digging through bureaucratic gibberish; like maybe sticking myself in the eye with a hot poker... :=(( Steve

 

[Rod Gervais]

Rod, thanks for the definition clarification on double framed walls - I was looking thru about 100 pages of chapter 7 of the IBC looking for just that - do you have an actual section number, so I can bookmark it? Or am I looking in the wrong place?

Steve,

Double framed walls are not listed (identified) in the codes - that because it is not considered "standard construction" - however - generally listed within the administrative code section - there is allowance for alternate methods,

For example (BTW - i don't have a copy of the IBC) in the UBC - section 104.2.8 is entitled "Alternate materials, alternate design and methods of construction" and 104.2.9 entitled "Tests" deal with this.

In the BOCA it's section 106.4 entitled "Alternative materials and equipment"

BOCA reads as foillows:

"The provisions of this code are not intended to prevent the installation of any material or to prohibit any method of construction not specifically prescribed by this code, provided that any such alternative has been approved. An alternative material or method of construction shall be approved when the code official finds that the proposed design is satisfactory and complies with the intent of the provisions of this code, and that the material, method or work offered is, for the purpose intended, at least the equivilent in quality, strength, effectiveness, fire-resistance, durability and safety."

Remember - the code establishes MINIMUM STANDARDS, you can always build above those standards, not a problem, it's just building below them which causes problem.

Beyond that you go to places like Underwriters Lab. (UL) and peruse their compilations of rated tested assemblies.

Any of those assemblies are acceptable to the code officials.

Rod

 

[knightfly]

Thanks Rod; since it's my understanding that the other codes have by now been updated FROM the IBC, I'll search that doc for "alternat", so it will pick up "alternate" and "alternative", maybe the same lingo will show up -

Also came across the UL site while checking on this, still gotta go there.

Thanks again man, hope you're getting at least a few minutes of "downtime", I know that's hard to do in your situation... Steve

 

[fitZ2]

Hey guys, although I can NOT post the links at the moment, (the links are on my FRIED computer ) I searched the net for some kind of illustration or code in regards to this, and found a couple of references to DOUBLE WALL/ insulation as Fireblock codes, relative to the city from which they are listed. What I found in 3 different codes, is that in THOSE CITYS, they permit fiberglass insulation as a fireblock between double PARALLEL walls, as long as it completely fills the airgap, at least 16" above the floorline. I'm going to check with my building inspection department and see what they say about this.
Sorry Michael, if I gave you information that was not totally correct in regard to codes, but I certainly am no expert in these matters, and so stated in my DISCLAIMER
I only tried to pass on information from my own limited experience, so I hope that what I told you didn't hamper you in any way. And thanks for the information Rod. This prompted me to further investigation so I will be better informed with my own project. Your experience in these matters sure help enlighten us DIY'ers.
fitZ

 

[ENIGMACODE]

Hello fitZ2, knightfly, Rod Gervais, and Michael Jones

fitZ2 you mentioned:

"What I found in 3 different codes, is that in THOSE CITYS, they permit fiberglass insulation as a fireblock between double PARALLEL walls, as long as it completely fills the airgap, at least 16" above the floorline"

Hey guys I really appreciate ALL your contributions here - however we've gotten AWAY from my main question. As I may have mentioned here, I am a 28 year licensed electrical inspector for the city of Philadelphia. And fortunately I work closely with my co-workers who are boca-certified building inspectors. However, their knowledge in Acoustical Engineering is limited. That's where guys like Rod Gervais, and Michael Jones REALLY fill the gap!

The outside wall that was referred to (above), is NOT a 'bearing wall' It's 'OK' with Boca (the local codes), as simply a 'FILLER' where the garage used to be! It's been insulated and rocked on the inside with 5/8 rock and there is an integral 'inner subwall' constructed 8" away from it as part of the main inside room assembly

I am more concerned with my ORIGINAL question - Aside from the aspect of 'appearance', I was asking if it is BETTER to rock the other sides of the walls (that I can get to easily), to add MASS to the other side of the wall?? (The outer side - opposite side) Here are my illustrations again:

Does it really matter in regard to these scenarios? Does it help?
As illustrated here:
http://home.ucwphilly.rr.com/livesound/par-combo-2.jpg
http://home.ucwphilly.rr.com/livesound/par-combo-3.jpg
http://home.ucwphilly.rr.com/livesound/par-combo-4.jpg
http://home.ucwphilly.rr.com/livesound/par-combo-5.jpg

*Please bear in mind that NONE of these NEW structures are actually fastened to the OLD existing structure of the house. I took GREAT pain to isolate the NEW walls with home-made iso brackets (as per Rod Gervais's advice)

Thanx again guys ..
Best Regards
Mike Fraticelli
ROCKON@ucwphilly.rr.com

 

[Rod Gervais]

Mike,

you never EVER want to put drywall in between 2 other leafs.

Picture it like this - your floor above is leaf one - and your (new) ceiling below is leaf 2 - the installation of drywall in the old ceiling location would create a 3 leaf system - and this decreases isolation.

So no - you do not want to put anything there........ in fact - you want to finish removing any of the old ceiling that is still in place (as I believe I saw in your photos.

As far as adding mass to the existing goes - you would be best suited (if you can) to place more mass at the top leaf (by this i mean the bottom of the existing floor deck) and sealing that in at the edges. This would help to create more mass in that location to prevent low frequency noise from passing through to the space above (or vis-versa).

The same goes for the walls - you want just 2 leafs to the assembly - and these on the outermost points of the walls.

In between - either standard insulation or thermafiber (if it fits within your budget) - the thermafiber will help a wee bit more with low frequencies than standard fluffy insulation will.

It's looking good by the way..............

Rod

 

[fitZ2]

Hi Michael, isn't it wierd how the direction and content of a thread can totally drift away from the original question, gain a life of its own character, and change the world Sorry about that.
Ok, I looked at the pics, and I'll throw my .02 in here, even though Rod, Steve, and Michael may have other thoughts on it. At least I learn that way too .
In the first picture. The ceiling. It looks like you have torn away an area to install some blocking to attatch the iso hangers from. AND, in picture(link 4)of the ceiling, this area looks quite extensive. My recommendation has to do with how much has been removed, and how difficult it is to remove the rest. And how much isolation do you really want. But DEFINITELY, I would NOT re-cover those areas. Just refill with insulation. This is why(my .02.) The flooring above is 1 leaf. Had it been me, I would have COMPLETELY removed the rest of the existing material that you started to remove, so I could line the CAVITIES between the joists, on the underside of the flooring, with 2 layers of sheetrock, and caulked. This would add mass to the first leaf(flooring). But it looks like there is insulation already, and it would be a chore to remove the rest of this membrane and existing insulation now(looks like plywood? ). The area that you have torn away,now vents into the cavitys, which is good. Had you left this membrane intact, it would become the second leaf, and then sheetrocked below it on suspended ceiling joists, this would now become a 3 leaf system. (NOT GOOD)Since it is NOT intact, the new drywall ceiling becomes the second leaf(GOOD), and the membrane in between becomes nothing, as it is NOT intact. Make sense? What I WOULD do, is drill some 1/2" holes through this membrane, in areas that may have blocking that prevents venting from the opening. Drill 4 or 5 holes the length of each cavity to make sure it is vented.
BUT. This does set up a scenario, which has to do with the area adjacent to the studio. It is hard to visualize direction of things in photos, like the direction of the joists. However, in the picture in Link 4 of the ceiling, I see a light from the adacent area, on the other side of the wall. This tells me flanking noise can enter(isn't this the area you were going to put an air conditioner)over this wall, and into the cavitys. I believe Steve has a recommendation for this on his forum. I believe it is part of the sheetrocking of the cavities I suggested, but don't hold me to it. Regardless, I think it should be taken into consideration BEFORE sheetrocking your ceiling.

Ok, pics on Link 2. Tough one. This still has to be delt with in regards to noise entering to and from the stairway from above, right? Still, it is hard to visualize the whole thing, as I cannot see how this wall terminates at each end. I would assume, there is a doorway at the bottom of the stairway, but what does this wall terminate into at the other side of the door, and at the other end? A double wall or what. It has to do with how I would treat this. In MY MIND, there are 2 scenarios I see. First, WHAT is on the OTHER side of the existing stairway wall? This would determine what I was trying to isolate(like street noise, or HVAC equipment, or LOUD speakers in an adjacent room,
It also has to do with the connections of this new wall at the ceiling too. AND, if there is a door at the TOP of the stairs.
this wall "decoupled" from the existing building? Or does it touch the stairway?
That is why I say TOUGH ONE, as it is hard to see everything. My experience with stairways tells me this wall EITHER terminates at the floor above, but another wall continues up the second floor in the same plane, or this NEW wall is actually 2 stories high, as it must be higher than a door opening above, correct? That is the problem. We need to see this condition above, at the floor line. But in the meantime,
if you considered the existing wall on the other side of the stairway as ONE leaf, then you wound need to leave the insulation exposed on the
stairway face of the new wall, DEPENDING on the above conditions. OR........
ALSO depending on the above conditions, I would PROBABLY make this wall a 2 leaf system, BY....#1. installing RC on the studio face of the wall and sheetrock with 2 layers of drywall, and rock the stairway side with 2 layers of rock fastened directly to the studs, BUT, this has to do with the connection OR non connection of this wall TO the stairs themselves, at the tread stringers. The reason I say the existing wall on the other side of the stairs MIGHT be considered as ONE LEAF, has to do with the width of the stairway, which in reality, MAY be considered as an AIRGAP, as even a room, such as your adjacent tool area in the studio might be this condition too, I don't know.

Well, Michael, I'm out of time, but I'll come back later to address the rest of this. Sorry. Hope this helps so far. Later.
fitZ

 

[knightfly]

Michael, got your PM - do you have specific questions, or just want my $.02 on all this? I'm just now getting over a 3-week bout with germ warfare, so I'm really behind on EVERYTHING in my universe, so if you could specify your question it would help me immensely - thanks... Steve

 

[ENIGMACODE]

Let's have a beer and relax

Hey Rod and fitZ2, and knightfly - thanx you all for your latest replies ...

Yes unfortunately I'm afraid we're all getting a little confused

However I think we can cut through and arrive at some conclusions .....

Michael Jones comments (below) were in regard to one particular outside wall (where my garage door used to be) as illustrated here: http://home.ucwphilly.rr.com/livesound/par-combo-1.jpg

Michael's response was:
"The outside, or exterior walls need to follow local building codes.
On the inside of my exterior wall, the cavity is filled with rockwool, then I have 1/2" drywall, 1/2" OSB, and a final course of 5/8" drywall"

Sooooo with Michael's comments, I went ahead and covered the rest of that inside surface with 5/8" as illustrated here: http://home.ucwphilly.rr.com/livesound/par-combo-1.jpg
Michael went on the say that since this was NOT an inside wall between a control room and a live room, it was ok to that ....

Now in regard to Rod's other comments:
"you would be best suited (if you can) to place more mass at the top leaf (by this I mean the bottom of the existing floor deck)"

This seems to contradict your next statement:
"So no - you do not want to put anything there........ in fact - you want to finish removing any of the old ceiling that is still in place (as I believe I saw in your photos"

That old plaster on the existing garage ceiling is one hell of a pain (I'm afraid it's gonna have to stay there)
But let me say that (I'm a bachelor), and the area above the music room is my own living room.

In the event that you were confused by the first illustrations, I'll create others here:
http://home.ucwphilly.rr.com/livesound/rod-1a.jpg
http://home.ucwphilly.rr.com/livesound/rod-2a.jpg
http://home.ucwphilly.rr.com/livesound/rod-3a.jpg
http://home.ucwphilly.rr.com/livesound/rod-4a.jpg
http://home.ucwphilly.rr.com/livesound/rod-5a.jpg

http://home.ucwphilly.rr.com/livesound/fitZ2-2-a.jpg

http://home.ucwphilly.rr.com/livesound/fitZ2-a.jpg

In general, I think I see the bigger here:
http://home.ucwphilly.rr.com/livesound/rick-combo.jpg
Do I take this illustration to mean:
JUST LEAVE ALL THE NEW OUTER SIDES OF ALL THE NEW WALLS OPEN WITH EXPOSED R11?
It's 'ok' because in regard to esthetics, don't forget I'm a bachelor

Best Regards
Michael Fraticelli
ROCKON@ucwphilly.rr.com

 

[Rod Gervais]

OK Buddy,

Let's see if I can clear this up.........

I wasn't contradicting myself - you read:

"you would be best suited (if you can) to place more mass at the top leaf (by this I mean the bottom of the existing floor deck)"

What you see is bottom of floor joist......... not what I said.....

I meant the deck itself - tight to the plywood - this increases the upper leaf - but does not create a 3rd leaf (no air space between the plywood and drywall).

So my following statement (which matches what fitZ observed) to remove the existing ceiling - is accurate.

I do not know about the code where Michael is - but nowhere that I AM aware of has any requirement that a bearing exterior wall requires more structural bracing that than afforded by the exterior structural sheathing - and EVEN IF IT DID - i could meet (or exceed) any requirements through the use of either let in structural frame bracing or metal T-bracing - so interior sheathing can't be a requirement - one easy way to meet the code - but not a requirement.

The code can only establish minimum requirements - it cannot stop me from using an alternate method that meets (or exceeds) the requirements if I can prove through accepted engineering practice that my systems work.

It's too bad you created a 3 leaf system - however - you live with what you must once things are done.

Sincerely,

Rod