John Sayers' Recording Studio Design Forum Archive

In my project, my roof is considered a third leaf -- even though the attic is vented and there is a lot of air in it and the distance between my "middle leaf" and the roof is between a few inches (where it meets the east wall) and about eight feet. However, Steve and I determined that these factors mitigated the third leaf effect, but did not totally eliminate it.

I totally get what you're saying about "true" third leaves... And I think we can all agree that a "true" sealed three leaf situation is a bad thing. What I believe you're trying to nail down is how much (if at all) a compromised third leaf (in terms of venting) would affect isolation, and I believe the answer to that would be that "it depends."

The IRC has done a lot of tests on many wall configurations, but I don't know of any official studies that get into these "untrue" third leaf situations... ...That's not to say that there aren't any, just that I'm not familiar with them if they exist.

I recall hearing that Paul Woodlock did some experiments with a door, moving it around a room to see how the existence of the panel affected isolation, and I recall the outcomes raised a lot of eyebrows in in terms of the negative effects it had... Not exactly bullet-proof lab test data, but perhaps interesting and noteworthy nonetheless.

Here's an interesting thread that Rod posted to over a year ago on the subject of third leaf situations. Check it out.

Funny... When I reread that post for the umpteenth time, I'm really starting to wonder now if my roof doesn't count as a third leaf... ...Man, this stuff gets complicated, doesn't it? )

Thanx Sharward:

I'm so glad that I feel understood now!
You've defined my ideas pretty much on the nail head.

Certainly we all must realize that, unless there is NOTHING between the outer (2nd) leaf and the outdoor world, ALL further barriers can -- in some way -- be considered 'quasi-leafs' if they don't create a sealed air space.
It would seem to me that very few studios are 'stand-alone' structures, that is, they are most usually housed within some other building.
But you can't get a double-wall effect within the building if you believe all the other, outer walls of the main building are REALLY true extra leaves that should be included in your leaf 'count'.

I mean, take the example of a HUGE cube-shaped room (isolated from the outdoor world) that has a much smaller studio-room in the dead center of it, somehow suspended so that there is an equal amount of air space above, below, and to all sides of it.
(assume the HUGE room is 100' x 100' x 100', and the studio-room is 10' x 10' x 10'; that would leave about 90 feet of air space between all faces of the studio-room and the HUGE room).

Now the studio room builders might say: "We can't make a double-leaf wall for the studio-room since that would constitute a 3-leaf system, because there is already a leaf in the HUGE room surrounding it!"

But we all 'know', almost intuitively, that if the builders make the studio-room single-leaf (and count the HUGE room leaf as the outer 2nd leaf), there would be much more sound transmission TO the HUGE room than if they 'ignored' the leaf of the HUGE room and made the studio-room double-leaf.

So, if we are just on the outside of the HUGE room, then a single leaf for the studio-room will complete a 2-leaf system; sound transmission to the outdoors might be quite low.
But, if we are in the HUGE room, then all that's between us and the inside of the studio-room is a single-leaf; sound transmission to the HUGE room would almost certainly be higher.

THE POINT?

If we need to block sound to the rest of a larger building that surrounds (or partially surrounds) the studio-room, then we HAVE to (to some extent) ignore some walls of the larger building when counting leaves.
This might be especially so if any of them are not 'true' leaves.

sharward wrote:In my project, my roof is considered a third leaf -- even though the attic is vented and there is a lot of air in it and the distance between my "middle leaf" and the roof is between a few inches (where it meets the east wall) and about eight feet. However, Steve and I determined that these factors mitigated the third leaf effect, but did not totally eliminate it.

I totally get what you're saying about "true" third leaves... And I think we can all agree that a "true" sealed three leaf situation is a bad thing. What I believe you're trying to nail down is how much (if at all) a compromised third leaf (in terms of venting) would affect isolation, and I believe the answer to that would be that "it depends."

Regarding 3 leaf issues, I think Steve (Knightfly) has suggested the best method of testing by ear 3 leaf effects, he wrote this on my thread:

Any weakening of the isolation due to resonant traps will always be a 2-way street. For a classic example of this effect, put a loud boombox in another room, separated from you by concrete block (hollow) - Hopefully this room has a door for more isolation from the room YOU are in -

pick up a 4x4 foot section of plywood or gypsum, hold it in front of you like you're gonna hang a picture on the intervening wall, and slowly walk toward this wall with the board in front of you - note which frequencies change in loudness as you get closer, right up til you actually TOUCH the block wall with the 4x4 board.

Note that the changes did NOT need a SEALED trap, only the air between the board and the wall... Steve

Note Steve referenced a hollow concrete block wall which is two leaf (well mostly 2 leaf). I do plan to try this test at some point when the rest my to-do list calms down.

I have previously thought about 3 & 4 leaf effect created from other walls and ceilings in a building, and I understand your thoughts...

Luftweg, even though I am not as inclined as you to question the "proven (suggested) isolation techniques", I do admire you passion shown from your writing and number of posts.

Ceiling height and many other things you need to know can be found in your local building code. For Florida I can find everything online.

I found this for your local building code:
http://www.mass.gov/bbrs/newcode.htm

Warning: that should be painful documents to sort through, mine was.

Marc

guitardad72 wrote:...
Luftweg, even though I am not as inclined as you to question the "proven (suggested) isolation techniques", I do admire you passion shown from your writing and number of posts.

Ceiling height and many other things you need to know can be found in your local building code. For Florida I can find everything online.

I found this for your local building code:
http://www.mass.gov/bbrs/newcode.htm

Marc

Hey thanx!
I was just looking for that....

Yeah, it seems the min height is 7 feet for a basement.
Although, I haven't found anything that deals with older construction waivers.
Maybe if the house is so old, then some rules can be bent....
In the area I live, you wouldn't believe some of the real old houses and the many short basements there are that are finished with short ceilings (way lower than what I would plan) -- and for years that way.
There's gotta be something, because otherwise there'd be alot of houses that would be in violation it would seem.

In any case, I would be able to do the between joist sheet-rock deal...
Have to figure how much weight 2 x 8 live floors can take however, and that may be a limiting factor....

btw, I had seen that link to an old thread where Rod addresses the very same issue (quasi-third-leaf) -- and it seemed to concur with my thoughts!

thanx,
K

alot of houses that would be in violation it would seem

YES a lot of houses are in violation either becuase they were built or work was done before a new code OR because new work was done without a permit.

I want to rip my hair out sometimes when it comes to my own house built in 1964, there are so many things not built to today's code, which I am slowly correcting where I can.

Although, I haven't found anything that deals with older construction waivers.
Maybe if the house is so old, then some rules can be bent....

A general comment, not a fact I know: it seems most new work has to comply with new code in most places. The only exception I can think of is when it comes to keeping a building historically correct, but even with that I'm guessing.

Marc

guitardad72 wrote:

alot of houses that would be in violation it would seem

YES a lot of houses are in violation either becuase they were built or work was done before a new code OR because new work was done without a permit.

Bingo.

When codes evolve, existing structures built to older codes do not become noncompliant -- they become, in effect, grandfathered. Typically code evolation applies to new work.

There are funny exceptions though... For example, in my town (and, for all I know, throughout California, or perhaps even throughout much of the US), any residential building permit requires that all sleeping areas in the home be equipped with smoke detectors (battery operated are OK). One cannot get a final signoff without them, even if the work has nothing to do with the bedrooms.

Also, some city or county governing bodies choose to amend the codes, either upwards or downwards, based on local conditions.

This is why it is always necessary to consult your local building department, because you never know if that thing you want to do that's legal everywhere else isn't allowed in your town -- or vice versa.

--Keith

bump for Knightfly.... thanx, K

Luftweg,

The drawing that you posted - where you have the 3 leaf system (and yes it is a 3 leaf system - even if it has the ability to breathe into other areas of the basement - this due to the fact that the air will still act as a spring..... but let's not even bother with that - because your design introduces other problems - code violations - that - once you solve them - will stop that air flow you seem to think helps you.

Wherever a wall meets a ceiling - it is required that you install a fire stop - this because allowing a fire to climb into (and above) floor assemblies (or attics) creates a chimney effect - feeding the fire instead of starving it.

Your detail "leaf joist cross-section 2a.jpg" creates this code violation in both ceiling sections.

This is the code requirement you have to abide by:

720.6.2 Connections between horizontal and vertical spaces: Firestopping shall be installed at all interconnections between vertical and
horizontal spaces such as occur at soffits over cabinets, drop ceilings, cove ceilings and similar locations.

I believe you said you have the book - look at the details in chapter 10 that show you where these firestops are required.

On to the question about member size - if your existing joists are capable of the load - why not just use 2x4's and support them in the intermediate spans with isolation hangers (see detail 4.25a in the book).

Then you don't have to concern yourself with sistering joists - or trying to invent some sort of quasi laminate menbers that you'll need engineering (to prove that they will work) for the building official.

Sincerely,

Rod

rod gervais wrote:
The drawing that you posted... is a 3 leaf system - even if it has the ability to breathe into other areas of the basement - this due to the fact that the air will still act as a spring..... your design introduces other problems - code violations - that - once you solve them - will stop that air flow you seem to think helps you...
Wherever a wall meets a ceiling - it is required that you install a fire stop - this because allowing a fire to climb into (and above) floor assemblies (or attics) creates a chimney effect - feeding the fire instead of starving it.

720.6.2 Connections between horizontal and vertical spaces: Firestopping shall be installed at all interconnections between vertical and
horizontal spaces such as occur at soffits over cabinets, drop ceilings, cove ceilings and similar locations.

I had seen in Sharward's studio thread (he is referring to a Canadian source):
"These findings indicate that, from an acoustics perspective, the best way of satisfying the code requirement for fire stopping is to use a double-stud wall with sufficient insulation so that the width of the air space in the wall is 25 mm or less. This approach does not reduce the effectiveness of the sound isolation of the wall assembly, and can actually improve it if the wall cavity is less than full to begin with. "

Is this true? Does blocking the spaces with fiberglass 'take care' of firestopping? (I guess this is a cue to contact the local building codes?)

I found this on the Mass. codes:
720.2 Firestopping materials: All firestopping shall
consist of approved noncombustible materials
securely fastened in place. Firestops of approved
noncombustible materials or of materials of two
thicknesses of one-inch lumber with broken lap-joint,
or one thickness of 23/32-inch wood structural panel
with joints backed by 23/32-inch wood structural
panel, or of two-inch lumber installed with tight
joints, shall be installed in open spaces of wood
framing.

Gotta figure this one out.... Might I have to use a single, wide top plate over both leaves of the wall?

Would love to totally avoid the 3rd leaf situation in the ceiling, BUT the diagram doesn't show the whole issue, which is my fear with the HEATING DUCTS, and capacity of the above floor joists (I felt that there would be a compromise in using a 'purely' 2-leaf esign, thinking it would really be like a 1.5-leaf system with respect to the ductwork)....

I suppose I should see what the existing weights are (but how do do that?); there is only a bedroom above for live weight, and softwood plank underlayment with red oak hardwood flooring.
I suppose I should be able to add 'some' sheetrock under the flooring....

rod gervais wrote:
I believe you said you have the book - look at the details in chapter 10 that show you where these firestops are required.

The book is on its way to me from Amazon....

rod gervais wrote: On to the question about member size - if your existing joists are capable of the load - why not just use 2x4's and support them in the intermediate spans with isolation hangers (see detail 4.25a in the book).

Then you don't have to concern yourself with sistering joists - or trying to invent some sort of quasi laminate menbers that you'll need engineering (to prove that they will work) for the building official.

Ah, I will look into the hangers when I get the book....
I'm seriously looking at using steel for the ceiling spans, since I have found span tables which show 4 inch deep members (of appropriate gauge and width) can run 12 feet and hold the sheet-rock.

thanx,
K

Luftweg,

I keep repeating to people the same mantra - but suppose I have to sit them down and make them breathe properly in order for them to get it.

I haven't gone through it yet with you - so I will now.

Repeat after me:

(while kneeling in the lotus position with your hands raised and the thumb with pointer finger forming an "O" - the remaining finger poined upwards).

Whatever I can make perfect I will make perfect - whatever I have to live with I will Live with.

Whatever I can make perfect I will make perfect - whatever I have to live with I will Live with.

Whatever I can make perfect I will make perfect - whatever I have to live with I will Live with.

Whatever I can make perfect I will make perfect - whatever I have to live with I will Live with.

Has sort of a soothing effect doesn't it? Bringing you closer to acoustic nirvana with every breath you take.

Simply put - just because you have to violate the 2 leaf system where duct exists does not mean that you are resigned to loose it's value everywhere else.

So everywhere that you can you develope the 2 leaf system - (saving a TON of money and labor in the process) and then - where you are forced - where you have no choice in the matter...... there (and only there) do you violate the 2 leaf system.

This maximizes your isolation while minimizing your investment.

See how easy it is?

Sincerely,

Rod

Received Rod's read yesterday -- learned several things in just a couple minutes flipping pages.... (i.e., it's already paid for itself in my opinion).

I will continue digging through it in the coming days.....

In other news, I dismantled some of the 'old' work (the insulation and studs and plates)...

My next question will be how to treat the concrete before I cover it up.
The house doesn't have a water or humidity problem (it's dehumidfied 365 days/yr ... course, it only goes on mostly in the summer).

The house is 1959-1960 construction and most likely has no barriers to vapor on the outside of the foundation (if that was even a thing to do).

Should I use anything on the inner face of the concrete, in terms of potential 'seepage', or any other treatment.
I'm thinking that the only area I should put a barrier is just under the sheet-rock, but over the studs.

thanx,
K

rod gervais wrote:Luftweg,
I keep repeating to people the same mantra - but suppose I have to sit them down and make them breathe properly in order for them to get it.
I haven't gone through it yet with you - so I will now.
Repeat after me:
(while kneeling in the lotus position with your hands raised and the thumb with pointer finger forming an "O" - the remaining finger poined upwards).

Whatever I can make perfect I will make perfect - whatever I have to live with I will Live with....

That's too funny!

Anyway, I tore out all the old studs and insulation (will try to re-use what I might be able to)....

The book is great, and I see the issues with the fire-stopping that I need to take care of (actually pretty straightforward it seems). Thanx for enlightening me.

EXISTING DUCT WORK:

I have decided, if cost is not ridiculous, to use the JM Superduct stuff to replace the overhead sections of ducting that runs under the joists and between them.
I will call a place called 'Homans' in Wilmington, MA to see if I can get the stuff there....

There is a main duct (8" x 14"), 2 square ducts (5") that run right over the middle of the room location (b/t the joists), and 2 circular (5") ducts that run right over the concrete walls by the last joist (always forget the name of that one).
Since the concrete is 12 inches thick, most of the duct is over the concrete wall, and the penultimate joist sits just a couple inches from the inside plane of the concrete wall.
Should I just then block off this area somehow, instead of trying to get sheet-rock b/t the joists? (might still be able to get the sheet rock up, but would HAVE to pull the ducts out I think... then should replace them with the JM stuff? $).

I want to decrease the depth of the main duct, but widen it to compensate the loss in area -- IF that's recommended -- something like 6" by 18"....
What do you think?

ABOVE FLOOR AS SECOND LEAF:

Obviously , I have also decided that turning the above floor into the second-leaf IS the best idea -- as I've been told, and now see in your book.
Anyway, I'm about ready to add sheet-rock to the above floor, b/t the joists.

JOIST STRENGTH AND SPAN:

I have pretty much determined that the floor and joists can 'take' it....
The above room is a bedroom (thus 30 psf live) with 3/4" plank underlayment and red oak hardwood floor, AND wall-to-wall carpet over that.

The joists are:
2x8 hem-fir (probably 'northern'),
straight grain, few if even any knots, no termite/pest or water/mold/rot damage, and are 'old' lumber circa 1959.
They appear to be an easy grade 2.
Span is 12 feet even on the longest side, and about 8 feet on the other side.

In summary:
live 30 psf, dead 20 psf, L360 deflection, gives 12' 5" as a maximum span for grade 2, 2x8 hem-fir at 16 OC..... If it's only 15 psf dead, it would give 13' 1".
Northern hem-fir would give the 14' 2" to 14' 6" range.

** Now questions about page 64:
You show a similar floor, but with 2x10's, that says with hardwood flooring the dead load is 8 psf.
1.) Since the 2x8's are lighter, would that mean the dead load would also be a bit less? (probably not all that much, huh?)
2.) If so, would that allow for the carpeting weight, and do you think that I likely could add 2 layers of sheet-rock between the joists (as an added 5.7 psf?).

.... Oh yeah, I am considering the Green Glue also, since I'm only using 2 layers.....

STEEL JOISTS:

Might try to get 3 layers on the inner-leaf ceiling, and go with 4 x 1.65 inch, 20 gauge steel joists -- may use 2 of those or some other 'boxed' or 'back-to-back' steel joists for increased strength/safety, IF that's feasible.
The reason for using steel is the desire for a somewhat shorter depth in order to save precious ceiling height (walls will still likely use wooden 2x4 studs)

CROSS-BRACING:

Finally:
3) Can I safely remove ALL the crossbracing when I add the sheetrock, or do I have to do one section at a time, replacing the cross-bracing after each section is done?

I intend to get some pics and updated plan diagrams up as soon as I can....

thanx for your help,
K

P.S.
I haven't forgotten about the HVAC for the room....
Keep in mind that this is going to be a single room studio, and as such I will only require 1 inlet and 1 outlet.
Also, I will probably wanting to be using the adjacent understairs area as a 'buffer' room that will house fans and such....
The remaining basement is dehumidified and cool 365 days of the year (probably due to the concrete, the surrounding earth, etc), so I'm initially planning on just 'equalizing' ventilation with the rest of the basement -- through isolated ductwork (as per your book)....

Luftweg wrote:I had seen in Sharward's studio thread (he is referring to a Canadian source):
"These findings indicate that, from an acoustics perspective, the best way of satisfying the code requirement for fire stopping is to use a double-stud wall with sufficient insulation so that the width of the air space in the wall is 25 mm or less. This approach does not reduce the effectiveness of the sound isolation of the wall assembly, and can actually improve it if the wall cavity is less than full to begin with. "

Is this true? Does blocking the spaces with fiberglass 'take care' of firestopping? (I guess this is a cue to contact the local building codes?)

I found this on the Mass. codes:
720.2 Firestopping materials: All firestopping shall
consist of approved noncombustible materials
securely fastened in place. Firestops of approved
noncombustible materials or of materials of two
thicknesses of one-inch lumber with broken lap-joint,
or one thickness of 23/32-inch wood structural panel
with joints backed by 23/32-inch wood structural
panel, or of two-inch lumber installed with tight
joints, shall be installed in open spaces of wood
framing.

Gotta figure this one out.... Might I have to use a single, wide top plate over both leaves of the wall?

When I met with the senior inspector at my building department, I asked about this, and he said I should be OK if I completely fill the gap between my walls with insulation. I told him I planned to use Thermafiber Sound Attenuation Fire Blankets (SAFB) - Nominal Density (2.5 pcf) or Roxul Acoustical Fire Batt (AFB) - ≥2" (2.5 pcf) and he appeared to be fine with that.

I will verify this with when I get closer to framing activities.

Either way, what's legal for me may not be for you, so yes, I would recommend consulting with your local building department.

--Keith

Here are some pics showing my issue with 'semi-hidden' ducts and their termination points, and the thickness of the concrete wall ....

The ducts are resting over the top of the concrete wall; only about 1.5 inches protrudes inside the plane of the concrete wall.
Now, outside of the duct is another joist, and on the outside of THAT joist (about 4 inches further, NOT 2 inches like the below pic says) is ANOTHER joist.

1.) Since there is no way I could avoid a 3rd leaf here, and since the duct only comes inside the concrete 1.5 inches (and my inner leaf stud wall will be well inside of that), should I just box off this whole area instead of going through the pains of replacing the duct and adding sheetrock to the above floor in that area?

2.) Could I use the lead I have to wrap those ducts? Would that pose a hazard somehow? (melting? etc.)

The concrete wall is 12 inches MINIMUM (actually 13 to 14 in most areas).

3.) With that much poured concrete, might I be better off just using that alone, even though it's a single leaf, since there is so much mass already? Would doing that avoid flanking up to the air space, between the above floor joists and the inner ceiling leaf? Will 3 sheets of gypsum of an inner wall leaf and and an air space really make all that much difference with so much mass in the concrete wall already?

Yet, I realize that there will be issues with adding inner windows, and perhaps with sealing the inner-leaf ceiling and opposing inner-leaf wall sheet rock to the concrete walls.... (will there be?)

Attached below is pic of a possible construction scenario for along the north-side concrete wall.

I have used Rod's book (Home Recording Studio; Build it like the Pros -- Rod Gervais, 2006; ISBN: 1-59863-034-2) as 'inspiration' for this idea...

Of course, it differs in some ways from the diagrams in his book, mainly because there are some differences in the existing construction of my basement.

The things I'm NOT so sure of here are:

1.) The firestop; is there a better place I should put it? Note that I don't show the blocking support for it, as frankly, I'm not certain where it should go.

2.) The sheet-rock along the 'penultimate' joist, and yes I realize that the space between it and the last joist constitutes a third-leaf, but there's really not much I can do about that.

3.) I intend to replace the old round metal duct with John's Manville SuperDuct -- IF I can ever find a place where I can get it ! (have tried a couple suppliers from the JM site; they said they contacted JM for me, and someone at JM told me they never HEARD of it, even though the JM website has pdf files about it!!).
Now, I don't know what I should do about the tapered connector from the old metal duct to the heat register; I'm wondering if I should just apply some of the superduct material to the outside of it, OR use some of the sheet lead I have, or......?
In any case, the gaps around this connector NEED to be treated in some manner.... perhaps I should pack them with rockwool...
Any ideas?

Note that I don't show any mid-span bracing for the floor joists (these WILL be re-installed after the sheetrock to the above floor is attached);
I can't really have the inner-leaf ceiling joists lower than pictured -- due to ceiling height concerns -- so bracing for these needs to be done differently.
These will be 4 inch by 1.68 inch, 20 gauge steel joists, as these appear to be able to give me the better strength, deflection, and span characteristics than wood joists of similar depth... again, the need for shorter depth ceiling joists is due to ceiling height concerns.

thanx for looking,
K