Feasibility of Isolating Studio Above Attached Garage

#16

Thank you for addressing the mix position question. I will come back to this in a later post. Onto the flooring assembly.

According to my structural engineer: "these existing floor joists would be able to withstand an additionnal unfactored deadload of 1.45 kPa (30 psf) if the load is applied all on the top chord." Based on the 30 psf limit this is what I have come up with.

0.75" maple hardwood finish over 2" Plywood (3/4" + 1/2" + 3/4" with Green glue in between.) over 2" OC703 over 1.75" Gypcrete over existing 1" OSB subfloor.

This will also give me 6.5" of rise to match the rise of the floor on the other side of the sunken landing adjacent to the studio.

I have never worked with Gypsum Concrete so if anyone can offer insight on prepping the subfloor and pouring Gypcrete that would help. Any other thoughts on this would be greatly appreciated as always.

I have sent my plans to Green Glue to see if they can offer more insight and I'm calling suppliers today regarding the gypsum concrete and OC703.

#17

"these existing floor joists would be able to withstand an additionnal unfactored deadload of 1.45 kPa (30 psf) if the load is applied all on the top chord." Based on the 30 psf limit this is what I have come up with.

When doing your calculations, it is easy to forget some major sources of weight.

For example, are you including your own weight, the weight of your desk, chair, equipment, racks, client couch, client(s), speakers, stray musical instruments, stray musicians, floor-standing treatment, lighting, decoration, etc. Adding all that up, you can easily find a thousand pounds or more. Did you take that into account when you did the math? What you are considering in terms of materials for the floor itself, is often referred to as "dead load": load that doesn't change, and is part of the structure. The other stuff is "live load", because it changes all the time, and isn't part of the structure. In some buildings, even wind pressure, snow on the roof, rain, and other natural sources, can be part of the "live load" (especially when considering roofing: not so much for flooring). So you should be considering both dead load and live load in your calculations.}}Also, if you are planning to build isolation walls that rest on the same floor system, that needs to be included. Ditto if you plan to flush-mount ("soffit-mount") your speakers: the soffits rest on the floor, and they cab be very heavy. Even without soffits, for "free--standing" speakers, you still need super-heavy speaker stands. Your engineer mentioned the dead-load, but he should also tell you about live load, or maybe just total load.

Maybe you already thought of all of that, and took it all into account, but I thought it was worth putting out a reminder, just in case. People often forget these details when thinking of floor load.

- Stuart -

#18

When doing your calculations, it is easy to forget some major sources of weight.

All load calculations were all done by my engineer.

The other stuff is "live load", because it changes all the time, and isn't part of the structure.

Live loads were considered and we did talk about this in person; however, she did not include live load numbers because as you say, they change. She didn't seem concerned with live loads based on how I described the use of the space, but this will be part of my follow up with her to see if I can get something in writing.

Also, if you are planning to build isolation walls that rest on the same floor system, that needs to be included

.
Yes, I will be working with her to plan the design of the interior walls and new inner ceiling. (I will post separately about wall and ceiling assemblies.) I expect the max dead load of the existing floor will change based on this so I will rework appropriately.

Maybe you already thought of all of that, and took it all into account, but I thought it was worth putting out a reminder, just in case.

Absolutely. Safety first. That is why I'm hiring an accredited professional to work the numbers for me.

As for the use of self levelling concrete (Gypcrete or other) do you have any insight or advice to share?

After a morning on the phone it seems the raw materials used in making Gypsum concrete are now hard to come by. One supplier recommends two alternatives for self levelling applications.

1. Ardex V1000 which apparently does not publish density data.
2. Mapei Novoplan 2 Plus which is a mixture of Silica Sand and Portland Cement and it has a cured density of 128 LBS/FT^3

Any thoughts on the Mapei Novoplan 2 option?

#19

Now onto a new ceiling assembly. What is shown in the pictures here is only approximate to help me visualize what may be involved. The plan is to get my engineer to draft proper plans and fully evaluate the loads involved. My starting point for this assembly is the notion that in a 3 leaf system M2 = M1 + M3 where:

M3 = Existing outer leaf
M2 = Middle leaf on bottom chord of existing roof truss.
M1 = New inner leaf

My engineers has determined ""possible to add an unfactored deadload of 0.85kPa (18 psf) on the bottom chord." for M2. It will be impossible for me to add mass to M3. Assuming there is nothing to be gained by making M1 > M2 in a 3 leaf system, and that most of the mass needs to go in the middle leaf, these are the numbers I have worked out for M2 and M1:

M3 = 3/4" OSB (2.5 PSF) + Asphalt Shingles (2.7 PSF) + Tar paper? (? PSF) = 5.2 PSF
M2 = 1/2" OSB (1.7 PSF) + 1/2" DW (2.1 PSF) + 5/8" DW (2.3 PSF) = 6.1 PSF
M1 = 2 layers of 3/4" OSB (5 PSF) + 3 layers 5/8" DW (6.9 PSF) = 11.9 PSF

Before I propose this to my engineer I would like clarification a few things:

Questions:
1. Mass in 3 leaf systems: I have read most of the Wyle report to gain insight on 3 leaf systems but its not fully clear to me. Is my assumption correct that there is little to be gained in making M1 (inner leave) greater than M3 (outer leave)?

2. Flanking at Apex: In the sketch I have included 2x12 blocking in the voids of the existing ridge beam (in yellow) to avoid creating a flanking path between it and the new inner ceiling rafters. The rafters would not touch the ridge beam and the only flanking path would be though the new knee walls (in white). This would add a lot of complexity when it comes to creating an air tight seal, especially if new collar ties (red) will be needed. But, it still could be part of the design criteria. Would there be much to gain in isolation by avoiding this flanking path?

3. Green Glue: I intend to use GG between all sheet layers. Does GG in a 3 leaf system offer benefits in all three leaves? Are the benefits of GG only effective in the middle leaf since this is where most of the mass goes?

#20

I am now also looking into isolated floor products offered by Kinetics Noise Control as recommended by Gullfo.

I'm looking at solutions that use their RIM products: https://kineticsnoise.com/rim/index.html
These use the KIP Elastomeric Fiberglass pads: https://kineticsnoise.com/kip/fiberglas ... -pads.html

Stuart, I'm hoping you could please shed some light on my previous questions regarding where in a 3 leave system most of the mass should be added, and what is the optimal ratio of mass between the different leaves. Also hoping to get your thoughts on what I'm proposing to avoid a flanking path at the apex of the new ceiling assembly. Any thoughts on the RIM and KIP products by Kinectics Noise Control would also be appreciated.

Thanks again!

#21

Stuart, I'm hoping you could please shed some light on my previous questions regarding where in a 3 leave system most of the mass should be added, and what is the optimal ratio of mass between the different leaves.

The ideal, according to research that goes back to at least 1973, is that the mass on the middle leaf should be the same as the mass on the other two leaves COMBINED, and those two other masses should be equal to each other. In other words: "M1 = M3 = 1/2 M2". Or said another way: "M1 = M3, M2 = M1+M3". For that layout, the two cavities must also be the same depth as each other (D1 = D2).

That's the OPTIMAL layout, but it doesn't mean that other layouts are out of the question. It's just the most effective one. If you have no choice, and have to put more mass on one of the other leaves, or less on the middle leaf, or one cavity depth has to be smaller, then you can compensate by changing one of the things that you DO have control over. As a general rule: Increasing any of the masses improves isolation in terms of dB, while increasing the depth of any of the air gaps improves isolation in terms of lower resonant frequency.

Also hoping to get your thoughts on what I'm proposing to avoid a flanking path at the apex of the new ceiling assembly.

Maybe you could show some more images for that? It isn't really clear to me what you are planning there, and I have a feeling you might be over-thinking it...

- Stuart -

#22

Soundman2020 wrote:As a general rule: Increasing any of the masses improves isolation in terms of dB, while increasing the depth of any of the air gaps improves isolation in terms of lower resonant frequency.

Gotcha. Do you know of any simplified equations that take all that into account?

Soundman2020 wrote: Maybe you could show some more images for that?

Sure. In yellow is the existing centra support beam. In blue are the new ceiling rafters. In white is wood blocking.

The blue ceiling rafters would not touch the yellow support beam at all as the white wood blocking is interleaved in the yellow support beam while not touching it.

Soundman2020 wrote: I have a feeling you might be over-thinking it..

Yeah I've definitely been known to do that haha. But as they say studio building is 90% design and 10% building, so I'm being as thorough as I can.

#23

Elusive Sounds wrote:Source of the post Do you know of any simplified equations that take all that into account?

There's no simplified equations, unfortunately. There are more complex ones that take into account more factors, and those are more accurate too, but not really needed for typical home studio applications. The full versions of the simplest equations for two 2-leaf and 3-leaf walls are these:

I've been working on a spreadsheet to assist in calculating this stuff and draw a graph that estimates TL, but I've been working on it for years, and still haven't gotten it to a stage that I feel comfortable with.... When I do, I'll post it on the forum, but for now it's just not there.

The blue ceiling rafters would not touch the yellow support beam at all as the white wood blocking is interleaved in the yellow support beam while not touching it.

OK, I think I get it now: You have an existing ridge beam that is basically a truss, and that supports your outer-leaf. Then you plan to build an inner-leaf ceiling frame , and instead of having a ridge beam for that, you plan to build a "box beam" that interleaves through the truss without touching it. Does that sound about right?

If that's the plan, then I'm not so convinced. From your diagram, it seems like the bottom chord of the new framing extends down lower than the bottom chord of the truss, and thus would be "inside" the inner leaf. That implies that part of your outer leaf would be inside the room? However, I also noticed that you are thinking of adding collar ties below that, and I'm assuming that the sheathing will go on the underside of your new rafter and collar ties? If so, that might work, but I'm not so sure of the structural issues, or even of that would pass inspection where you live. I would suggest talking to your local structural engineer, and running that by him to see if it will work structurally, and if it complies with your local building code. He might even be able to suggest a better way of doing it, without all the complexity. Also, that is not going to be easy to build at all, working in the very confined space up there at the apex of the roof. You might find that it can't even be built in practice, due to lack of space to get the materials up there and then work with them.

Just some things to think about!

- Stuart -

#24

Soundman2020 wrote: OK, I think I get it now: You have an existing ridge beam that is basically a truss, and that supports your outer-leaf. Then you plan to build an inner-leaf ceiling frame , and instead of having a ridge beam for that, you plan to build a "box beam" that interleaves through the truss without touching it. Does that sound about right?

Exactly.

Soundman2020 wrote: it seems like the bottom chord of the new framing extends down lower than the bottom chord of the truss, and thus would be "inside" the inner leaf. That implies that part of your outer leaf would be inside the room?

I'm not sure I understand this. Let me try to clarify in this image:

In pink is the new inner wall of the MSM wall assembly. In green is the bottom of a bulkhead (or soffit) that would be built around the existing central beam. Of course a bulkhead could only be constructed if new collar ties (in red below) are not structurally required.
If new collar ties are necessary I hope to use the space identified with the X for fresh air ducts. If no collar ties are needed I would fill this space with bass traps.

Soundman2020 wrote: I also noticed that you are thinking of adding collar ties below that, and I'm assuming that the sheathing will go on the underside of your new rafter and collar ties?

In the case that collar ties are needed, yes the inner leaf sheathing would be below them. In the case that collar ties are not needed; and that a bulkhead can be built, the sheathing would be under and around the bulkhead.

Soundman2020 wrote: I would suggest talking to your local structural engineer, and running that by him to see if it will work structurally, and if it complies with your local building code. He might even be able to suggest a better way of doing it, without all the complexity. Also, that is not going to be easy to build at all, working in the very confined space up there at the apex of the roof. You might find that it can't even be built in practice, due to lack of space to get the materials up there and then work with them.

Yes my intention is to bring this to my engineer to address all these concerns. But I only want to bring it up to them IF all the trouble and complexity of avoiding that flanking path would give me better overall transmission loss. So assuming all structural and code issues can be met, do you think avoiding the flanking path would indeed give me better results then if the new ceiling rafters were attached directly to the existing central beam?

#25

Hey folks! This thread / build is still alive. Received some design details from my engineer, progress on the outer shell is coming along, electrical works and more design details are being worked out. More soon. Cheers.

#26

That's great news. I love the workaround you have designed to allow the inner structure to be kept isolated from the centre support beam!

Cheers,
Jennifer

#27

I have been deep into researching fresh air needs for my space and this is what I have come up with so far:

Room volume ≈ 3600 FT^3. As per Stuart's 6 air changes per hour that equals 21600 FT^3 of air circulation, divided by 60 minutes = 360CFM of circulation. Stuart's rule of thumb is that 20-40% of that number is the required fresh air needed. As I will be alone in the space most of the time Im opting to use 20% of 360 CFM = 72CFM. In his book Rod Gervais uses the approximation of 15 CFM per occupant while Stuart uses 10CFM. I can't imagine I will ever have more than 5 people playing music in here at the same time, while the airtight doors need to be closed... But those numbers brings my fresh air requirement to between 50-75CFM which is close to my initial estimate of 72CFM.

As for keeping fresh air and return air flow rates at or below 200Feet/Min:
72CFM/200FM = 0.36F^2 = 51.8 IN^2 cross sectional area
which mean I would need a 7" square duct or an 8" round duct.

At this point I am leaning towards not building a second inner ceiling assembly which would force a triple leaf and eat up too much space. I am now considering merely going with the 2 layers of plywood and 3 layers of 5/8 DW under the bottom chord of the existing roof Truss. I would use 3 tubes worth of Green Glue per 4'x8' area between those five layers of sheet materials. I'm trying to get someone from Green Glue / Certainteed / St-Gobain on the phone about their thoughts on that.

My engineer has also clarified that the existing collar ties do need to stay in place. So I'm now thinking of exposing the collar ties and use them as an architectural feature that would be visible - I think they would look good stained... The 5 layers of sheet material would then follow the bottom chord of the webbed truss, up to the central support beam and wrap around the beam as pictured:

This would create a triangular space above the collar ties, below the inner leaf ≈ 18" wide, 16" high having a cross sectional area of ≈ 144 IN^2. This is about 3 times my required cross sectional area for 200Ft/Min velocity. So the idea would be to use these triangular spaces as expansion chambers to further lower my air velocities. The inside of these triangular voids would be lined with 2" of duct liner.

As for baffle boxes - That is the next thing I'm looking into, but I wanted to ask for your thoughts on if the above plan seems to make sense for the fresh air expansion chamber right before the air is dumped into the room. If this isn't silly, would it also be a decent place to also put my inner leaf baffles as well? The length of these triangular space is quite long.

I've also made progress on finding a suitable ERV. This Panasonic unit seems like my best bet, it has the form factor and feature set I'm looking for in my cold climate. https://na.panasonic.com/ca/indoor-air- ... 50-100-cfm

Notably it has separate and variable fan speeds. It drops as low as 50CFM for when I will be working alone (which I feel is still more than I need, but....) then I can boost to a higher setting whenever the occupancy requires it.

Would love to have your feedback about where I'm headed.

Feels good to be focused on this project again!

#28

i generally use 35% for my fresh air component. that said, if you can use in-room ceiling soffits (absorption, routing of things etc), then you only need to penetrate the room twice - one for supply and once for return - and then use larger ducts and plenums in the soffit to distribute and expand to reduce speed. using flexible duct or duct board - the soffit will still provide good LF absorption.

#29

Here is a first sketch of the Fresh Air supplies and Stale Air return along with the four baffles. From the ERV Id use 6" flex duct up to the outer leaf baffles. I'm now considering using 2" duct board to build the baffles. I would again use 6" flexible duct at the penetrations of the inner and outer leaves. (Only the outer leaf wall in green is pictured here):

The Stale Air Return opening would be made directly out of the inner leaf Stale Air Baffle. That opening would have roughly 3x the cross sectional area of the opening at the wall penetration to lower the return air velocity.

The Fresh Air Inner Leaf Baffle would feed a triangular shape duct.

That duct would then branch out via 6" flex duct to two symmetrical outlets, lowering the fresh air velocity even further.

Questions:

1. In the mechanical room where the ERV is located, would it be ok to fabricate the outer leaf baffles exclusively from duct board or do I need the line the boxes with substantial mass? I don't care about finishes here. Since these baffles are outside the MSM system do they need extra mass?

2. What is the best way to handle the penetrations between inner and outer leaf baffles? Any picture examples?

3. Does it look like my Stale Return might be too close to my Fresh Air supplies?

#30

1. once you're away from the noise sources you don't really need the additional mass
2. the space between the boundaries - you should encase without coupling the two side with the flex between. this can be a nested set of ductboards with some ply or drywall on the outside. or in my example if the units simple sit on either side of the boundary, then a simple passthrough suffices.
3. you should have supply and return separated sufficiently to ensure movement across the space so as much as possible the entire space if properly vented without "pockets" of stale air.

here's the example i was referring to wrt the room soffit housing the plenum. there are a lot of advantages to having a soffit running around the edge of the ceilings as you get absorption and routing.

Soundman2020 - Studio Design Forum