2nd Floor Studio Build Project Above Detached Garage

[infinitystairs]

Hi everyone, this is my first post but I have been devouring all the great info on this site, and I've read Rod Gervais's book several times. I'm starting construction on a home studio project in two weeks, and I'd like to get some feedback.

The Building
My first big challenge: My house has a detached two-car garage, and a second floor unfinished space that I plan to build into a home studio. I hope to achieve as much sound reduction as possible. I know that being on the second floor will create a difficult challenge.

Floor plan is attached, 22.5'x21'x9'. 469 sq ft, consisting of a large single room plus a small half-bath. The building can be described as "over built" with the first floor sitting on 2x6 posts and the second floor sitting on 2x10 joists. For a wooden two story garage it feels solid as a rock. The engineer, from a load perspective, said I can do anything I want up there.

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Intended Use
I plan to record and practice with rock bands playing typical, loud rock band volume. I live in the core of the city, not overly "quiet" neighborhood but still residential and pretty close to neighbors that I don't want to disturb, about 50' - 150'. I measured drums in the unfinished room = 115db; directly outside of room with door shut = 80db; and in the driveway near neighbors house = 60db. No drumming, just ambient neighborhood measured 48db.

Budget
$10k - $15k, but I want to keep it as budget-friendly as possible.

PLAN DETAILS
The walls: I plan to use GenieClips to decouple the drywall, and to drywall over the existing windows, using two layers of 5/8" drywall with Green Glue on the inner leaf.
[*] Any feedback on GenieClips as compared to some other clips? I initially was leaning toward staggered studs from a budget and simplicity standpoint but I'm concerned about the flanking through the shared top and bottom plates and into the wooden floor.
[*] The outer leaf is just the existing exterior wall, consisting of siding material and sheathing. I'm concerned about the added build complexity of stuffing strips of drywall in between the studs. Can I leave the exterior walls as-is or would it be important to fortify them? Would my time/money be better spent on a third layer of drywall on the inner leaf?
[*] I plan to install a half-bath in the corner of the room. I don't want to add the extra leaf to the interior-facing bathroom walls, so I'm trying to figure out how my decoupled inner leaf wall should be arranged around the bathroom wall frame which would interrupt it? Would a single leaf bathroom wall that is touching my decoupled wall short-circuit it?

The ceiling: I have a pitched roof, and my contractor and I have decided we can raise the ceiling joists several feet to create a semi-vaulted 13' ceiling. I need to vent the roof decking, I assume with inlets in the eaves and a ridge vent, which renders my roof useless for sound isolation.
[*] If I just attach isolation clips to the roof joists and newly raised ceiling joists, and cover it with two layers of 5/8" drywall and Green Glue, is this good enough? It seems like it is essentially just one leaf due to the attic venting. If it is important to add another leaf, I'm not sure where to add it?

The floor: This seems like my biggest concern. The garage below is unfinished. I don't care if it is loud in the garage but I think if sound moves through the floor it will just resonate in the garage and escape. I plan to insulate and drywall the garage ceiling.
[*] I need help here with the studio floor design. Do I just need to add mass, or somehow isolate or float it? Any recommendations?
[*] 1st floor garage ceiling - do I really need to go all out with isolation clips, double drywall, and Green Glue? Or can I get away without some of that added cost?
[*] 1st floor garage walls - can I get away with leaving them unfinished?

HVAC: I have a mini split which I plan to install, and I was considering adding an ERV to bring in fresh air.
[*] The mini split would be hung on the decoupled inner leaf wall which is hanging on GenieClips. The mini split is supposed to be mounted to the wall studs through the drywall. Won't this compromise my inner leaf decoupled wall?
[*] I am looking at Panasonic WhisperComfort ERV. Any feedback on that model? It looks like 20 CFM is right for my sized room.

Apologies for the long list of questions. I am very excited to get started on my project with the help of this group. You are an amazing resource!

[Waka]

Hi there Infinitystairs,

Welcome to the forum. You have a nice looking space there to practice in! You mention you wanted to record in there, does that mean you would also like to mix in there?
Mixing/critical listening rooms are alot more intricate to design. So if you plan on mixing, you had better start there in your design.

You're on the right track in some places. You mention that you want to reduce sound escaping your studio, but the measurements you provided at your neighbours border shows only 60dB as it is needing only another 12dB of isolation to blend in with surroundings. Is that C weighting on Slow response on your sound level meter? (you didn't use an app did you?)

Also you're really going to struggle if you're starting construction in two weeks. You don't have enough of your isolation design sorted yet.

When you're building a decoupled 2 leaf assembly (with genie clips or staggered studs etc.) you need to have significant mass on both leaves for it to be effective. Each leaf also needs to be completely sealed.

What are you doing about the door? That's a significant weak point. There's no point adding mass to your walls if it will just escape through the door.

Decoupling with genie clips will probably be fine for your build if you really only need another 20dB of isolation.

The problem you have is your ceiling. You're right, a vented roof cannot be used as an outer leaf. Therefore you need to board the bottom side of your roof joists completely air tight with additional mass. Then you need to have a second decoupled ceiling leaf that doesn't touch your outer leaf.

This is usually why the recommendation is to build a room-within-a-room. Your inner leaf ceiling joists will sit directly on the inner leaf framing.

If you go with genie clips you will need to be very careful to seal where the inner ceiling meets the inner wall leaf.

You also won't have much of a cavity of air between the leaves for damping sound transmission.

Your floor is an issue really. At the moment it will act as a drum skin and will resonate heavily. And it is a direct flanking path to your outer leaf. As your requirements are quite low, you may get away with doing a light(ish) weight floating floor. But it won't be nearly as effective as a proper reinforced concrete floating floor.

An example of a simple floating floor design is in John's recording manual:

http://johnlsayers.com/Recmanual/Titles/Acoustics3.htm

The plywood design should be enough for you (unless 20dB of additional isolation isn't actually enough)

Your mini split is a good idea, but you need to "snake". The pipes within the wall cavity a couple of feet, to offset the holes and caulk around the pipes,. The ERV is the more involved process though. What do you do about the giant holes you need to cut in your walls/ceiling? You need to replace that lost isolation, this means silencer boxes! Search this forum for examples. You need at least one per hole (only for low isolation, an additional one for each leaf is needed for higher isolation).

Before you build anything though, seriously consider putting off your builder. Your don't have enough design ready yet, and your will make it hard for yourself and more expensive in the long run.

If you do want to do something now though, first of all you need to get a good silicone caulk (if you don't need to paint over it) and caulk every single crevice/joint and crack in the walls, ceiling, windows and floors.

Let us know how you're getting on.

Dan

[infinitystairs]

Hi there Infinitystairs,
When you're building a decoupled 2 leaf assembly (with genie clips or staggered studs etc.) you need to have significant mass on both leaves for it to be effective. Each leaf also needs to be completely sealed.

What should I do about my outer leaf walls? I'm concerned that the existing outer leaf of siding and sheathing isn't very sufficient, but the idea of pushing drywall into the stud cavities seems labor intensive. Do I need to do anything more here?

What are you doing about the door?

I'm planning to use a solid wood door and the PDS Threshold and PDS Light door seal products from IsoStore. Should that be sufficient?

Your inner leaf ceiling joists will sit directly on the inner leaf framing.

If I was doing a second wall frame inside the room I could see how I would build a second ceiling frame on top of that, but I'm having trouble picturing this design if I am using GenieClips on the walls. So I would have existing vented roof + airtight drywall directly on existing joists + new inner leaf framing... attached to what?

As your requirements are quite low, you may get away with doing a light(ish) weight floating floor. But it won't be nearly as effective as a proper reinforced concrete floating floor.

An example of a simple floating floor design is in John's recording manual:

http://johnlsayers.com/Recmanual/Titles/Acoustics3.htm

I was considering a design similar to John's concrete floor. Thoughts on using several layers of HardieBacker cement backerboard on top of two layers of fiberglass with fiberboard sandwiched between?

The ERV is the more involved process though.

Is an ERV overkill for a single 450 sq ft room? Is there a more passive ventilation design that would suffice for my fresh air needs to compliment the mini split?

If you do want to do something now though, first of all you need to get a good silicone caulk (if you don't need to paint over it) and caulk every single crevice/joint and crack in the walls, ceiling, windows and floors.

I've seen some debate on butyl vs silicone vs acoustical caulk. Any advice on what I should use for filling crevices and around the perimeter of my interior leafs?

Thanks!
Graham

[Waka]

Sorry for the delay. Has been a busy week.

What should I do about my outer leaf walls? I'm concerned that the existing outer leaf of siding and sheathing isn't very sufficient, but the idea of pushing drywall into the stud cavities seems labor intensive. Do I need to do anything more here?

Again, this depends a lot on how much isolation you really need. The measurements you gave before, of a 35dB transmission loss with the current construction, which drops another 20dB over the distance to your nearest neighbour's boundary, are pretty good if all you need to do is reduce the noise escaping your room. You say ambient neighbourhood is 48dB, is this the loudest it gets? Think about lawnmowers, lorries, planes overhead, sirens? You may want to increase the isolation in the studio to prevent external noise interfering with your recordings.

The best way to determine how much isolation you should get is to to run the calculations on your planned construction. Our own Greg has made a handy Transmission Loss calculator (with the help of a spreadsheet guru). Here's a link to it: http://johnlsayers.com/phpBB2/viewtopic.php?f=1&t=21770. Bear in mind, the calculator offer theoretical results that may be off due to multiple unknown variables. If yo read the instructions once or twice it's pretty self explanatory how to use it.

The idea of pushing drywall in between the studs is indeed labour intensive, but I guarantee you the biggest headache is having to caulk ... everything.
Here's one I made earlier...

finished caulking lowers 2.jpg

I'm planning to use a solid wood door and the PDS Threshold and PDS Light door seal products from IsoStore. Should that be sufficient?

Run it through the calculator . But I doubt it will be, you're not likely to get above 40db or so of transmission loss with a single solid wood door. You might get away with a lead lined "super door" (see Rod Gervais' book). But even then it will be pushing it to achieve 50dB or more. It's usually easier (ie. better) to fit two standard solid wood doors (with seals) back to back, and beef them up with additional heavy ply/mdf if necessary.

If I was doing a second wall frame inside the room I could see how I would build a second ceiling frame on top of that, but I'm having trouble picturing this design if I am using GenieClips on the walls. So I would have existing vented roof + airtight drywall directly on existing joists + new inner leaf framing... attached to what?

If you were doing genie clips, you wouldn't have an inner leaf framing for your ceiling, you would genie clips on the ceiling too. I haven't checked the data, but genie clips probably won't give you more than 40-45db of isolation at bass frequencies (Correct me if they have independent data saying they do). If that's enough then you have an easier job on your hands, so go you! If not though, then you need to redesign for room-within-a-room.

I was considering a design similar to John's concrete floor. Thoughts on using several layers of HardieBacker cement backerboard on top of two layers of fiberglass with fiberboard sandwiched between?

That might, but I've never seen a design using this. You can be a trail blazer ( ), and let us know if it works! It would probably be somewhere in between the two designs John hghlights (Plywood and concrete), The problem would be more to do with structural integrity though I imagine, You would probably have to sandwich the cement board layers between two layers of plywood to stop it breaking apart. When you start getting this weight though, you need to check again with your building inspector/structural engineer. You need a number fromt hem, them saying you can do pretty much anything isn't a lot of good, because you may have wildly different ideas of what you're going to be putting up there; he might just be thinking you're asking about laying a rubber "acoustic pad". Ask him how many additional kg/m2 or lb/ft2 the construction can withstand.

Is an ERV overkill for a single 450 sq ft room? Is there a more passive ventilation design that would suffice for my fresh air needs to compliment the mini split?

Not really. Active ventilation is pretty much required in a sealed studio. If you want to reduce costs (up front) you can just fit a large extractor instead of an ERV. You need to calculate to completely replace the volume of air in the room 6 times an hour (at least), for comfort. Obviously, an extractor fan is not going to help with your heating/air conditioning energy usage.

I've seen some debate on butyl vs silicone vs acoustical caulk. Any advice on what I should use for filling crevices and around the perimeter of my interior leafs?

I haven't used butyl caulk myself, but I've read that it can shrink whilst curing. Acoustical caulk, is good because it's cheap (if you buy in bulk) and over-paintable, but in my experience it was very weak when it comes to flexibility, I had some cracking issues with mine, especially where a plasterboard was cut and there wasn't a paper covered edge to seal against.
Silicone sealant is extremely good at sealing. You need to get the right type though, you need to the low-modulus flexible stuff. The density of the sealant is generally secondary as opposed to it's ability to remain air-tight. You are sealing generally in corners/over studs, so you have significant mass already in those areas, what's most important is keep the seal, no-matter the humidity, weather, or building movement. Silicone meets those requirements. Always get a coloured variant (not clear) as it is of greater mass (might as well right?).
The downsides of silicone, are mainly cosmetic. You can't sand it down, you can't (generally) paint over it.
There are some very very good (but expensive) sealants that combine all of benefits of silicone, but can be painted and used in the wet etc. An example that I used on my exterior door frame: http://www.geocel.co.uk/catalogue/singl ... t-adhesive.

You will be spending an inordinate amount of money on sealant, so maybe grab a few locally to try before buying in bulk (I spent over £200 on caulk/sealant, in my build).

Dan

[infinitystairs]

The ceiling: I have a pitched roof, and my contractor and I have decided we can raise the ceiling joists several feet to create a semi-vaulted 13' ceiling. I need to vent the roof decking, I assume with inlets in the eaves and a ridge vent, which renders my roof useless for sound isolation.

I just had a breakthrough in thinking about my ceiling. I assumed because we were doing a half-cathedral ceiling that the roof deck had to be vented. I have read up on some experts that make a case for a non-vented roof. Using closed-cell polyurethane spray foam creates an air-impermeable roof assembly that does not need to be vented.

My problem with this approach is that spray foam is not considered a good approach to soundproofing because it lacks mass. Then I ran across a method called "flash-and-batt" in which you apply 1 to 2 inches of closed cell spray foam to the exterior wall, and fill the remainder with standard fiberglass batts.

Here is a great article on the subject. See page 3, "Can I build an unvented roof assembly?" and page 4, "If I use a combination of foam and fluffy insulation, how thick should the foam be?" http://schluebarchitecture.com/resource ... ov2011.pdf

I'm pretty excited about the flash-and-batt approach. It seems like best of both worlds, in which my outer leaf roof deck is airtight and doesn't have to be compromised by vent holes, but I still am able to leverage the benefits of loosely filled fiberglass insulation.

From outside to inside, the layers of the cathedral ceiling would be: Roof assembly on 2x8 rafters > 2 inches of closed-cell spray foam > R19 fiberglass batts > GenieClips > Hat Channel > 5/8" drywall > Green Glue > 5/8" drywall.

Any feedback on this approach?

[Waka]

Hi there again,

A similar roof approach to the one you are considering is sometimes called a "hybrid" roof:http://www.architecturetoday.co.uk/roof ... -practice/

The idea is to place enough insulation above the roof deck to prevent the deck being at dew point temperature.

Your approach seems to just be attempting to waterproof the roof deck underside. You will still get condensation on the underside of your spray foam (unless it's ridiculously thick) which might affect your roof joists/rafters themselves.

I would be more inclined to add celotex insulation panels on top of your roof deck (then a suitable covering) and fluffy insulation below the roof deck for the cavity.

But check with your local building inspectors as to what is acceptable in your climate, that meets building standards.

Dan