Greetings and a Question or two (or three)

[SoWhat]

Greetings all,

First, thanks to Stuart for the Forum.

I'm about to commence a studio build here (just outside Philadelphia). The space will mainly be used for solo practice (drums, piano), but will also occasionally host small jazz and rock groups. I'm expecting no more than 110db max sound levels. The close neighbors' house is about 35 feet away, and the neighbors on the other side are at least 75 feet (not too sure because their house is below ours, by a good distance).

The building will be a converted 20' x 24' X 12' 6" free-standing pre-fab two-car garage/workshop with NO GARAGE DOORS (one less thing to worry about), no exterior windows, and built on a reinforced concrete slab. Studs are 2x4, 16 OC.

My plan is to add mass to the exterior (it's just sheathing and OSB) with two layers of 5/8" drywall between the studs.

Will build room-in-a-room with staggered studs, two layers of 5/8" Fire X with Green Glue on the inner leaf, and about a 3" air space between the exterior and interior walls. Of course, the appropriate insulation in between. I think that's everything, although I'm sure I missed something.

Now the questions:
1. I want to build an airlock-type entry, but in my search through Rod's book and the multitude of forums (GS, etc), I can't seem to figure out if I need to build a double-wall system for the walls of the airlock, which I assume should be attached to the inner leaf. What is the answer to this?

2. Can I use a standard solid-core metal exterior door as the exterior door (the outer leaf) while using a solid wood door for the inner leaf?

3. For the beefing of the exterior wall, what's the best way to fasten the drywall to the OSB? Does it need to be screwed on? I saw the example in Rod's book of the caulk-in-place, but I'm not sure if that was the only thing holding the two drywall layers there.

Thanks very much indeed.

All the best,

Paul

[Starlight]

Hello Paul. I am certain that Stuart will be here with his professional advice before long. In the meantime, just a couple of things.

Source of the post1. ... airlock-type entry ...

Are you planning for the airlock entry to be attached to the oustide wall, like a porch? Or will it be attached to the inner wall, like a vestibule?

Source of the post2. ... solid-core metal exterior door ... solid wood door for the inner leaf?

The ideal situation would be to have doors that match the mass (per square foot) of the wall they are each attached to. No doubt, Stuart will explain in more specific detail.

Source of the post3. ... what's the best way to fasten the drywall to the OSB? Does it need to be screwed on?

Have a look at the relevant photos in posts 20, 21 and 34 of my build topic, here, as they will show you multiple layers of drywall being screwed onto OSB using drywall screws, mud and tape, backer rod and acoustic caulk.

All the best with your studio.

[SoWhat]

Greetings Starlight,

Thanks for the response.

In my question about the airlock, I assumed it would be attached to the inner leaf. I hadn't thought about doing it the other way.

After all of the reading I've done here and on other forums, you'd think I'd know that the doors need to match the wall mass they are attached to. Thanks for the reminder I shouldn't have needed!

I will check out your build link, thanks.

All the best,

Paul

[Soundman2020]

Hi Paul, and Welcome to the forum!

Congratulations on your project!

Starlight is already giving you good advice, so I'll just add some more comments to what he already said.

...host small jazz and rock groups. I'm expecting no more than 110db max sound levels.

For jazz, that's probably about right, maybe even a little high, but for contemporary rock groups the levels could go higher than that. It's not unusual to be approaching 120 dBC inside the room, especially if you have a heavy-hitting drummer, and a bass player who likes to "turn it up to 11". To be certain what your real levels will be, it would be good if you could take a sound level meter into your next practice session with your band, and measure the actual levels in there (set the meter to "C" weighting, and "Slow" response).

The building will be a converted 20' x 24' X 12' 6" free-standing pre-fab two-car garage/workshop

That's a nice size! Especially the height: having a high ceiling is always good for live instruments. It seems like your studio can be quite good, acoustically!

My plan is to add mass to the exterior (it's just sheathing and OSB) with two layers of 5/8" drywall between the studs.

That is often called "beefing up the mass", and there's a simple procedure for doing that: cut the strips of drywall just a fraction smaller than the stud bay, press it in place against the OSB, caulk around the edges (with any good-quality kitchen or bathroom caulk that is very flexible and remains soft and rubbery even when fully cured), then use "cleats" nailed sideways into the studs, to hold the drywall in place. Don't nail through the drywall into the OSB! So the drywall will just be pressed up against the OSB, held in place by the cleats, and sealed around the edges with caulk. If you want even better isolation, the use Green Glue compound between the drywall and OSB, then again between the second layer of drywall and the first. Green Glue is effective, and works as advertised, but it's not cheap.

Will build room-in-a-room with staggered studs, two layers of 5/8" Fire X with Green Glue on the inner leaf,

Your mention of staggered studs makes me wonder if you might be misunderstanding the concept of "room in a room". You only need a total of two "leaves" here, and your existing garage IS the outer leaf. Or rather, it will be the outer leaf once you "beef it up", as above. So you only need one additional leaf to complete the system: just a simple single-stud frame with drywall on only one side of that frame (not both sides). That's your second leaf: the "inner" leaf. In other words, there is no need for a staggered stud frame here.

Here's a diagram to show you the concept:

That doesn't show exactly your situation: rather, it shows the situation where somebody wants to section off part of the garage or basement to use as a studio. But you can still see how this works. In your case, the inner room (at the back) would be larger, filling the entire garage space, and you would not need the partition wall that sections off that part... I'm sure you can picture that in your mid. Think of it like a "matchbox inside a shoe-box". The "shoe-box" is your existing garage shell (beefed up), and the "matchbox" is what you build inside of that.

and about a 3" air space between the exterior and interior walls.

There's some simple equations for calculating the optimum size for the air space, based on the amount of isolation you need, and the frequency range you need to isolate. This type of construction creates a tuned system that resonates at a low frequency, so it is important to design it so that the frequency is low enough. The air gap is a key part of that. I should also mention that this whole "air gap" thing is also confusing, since there are several things that this term could refer to, but the important distance here is the distance across the wall cavity from the outer leaf to the inner leaf, and not just the distance between the two frames. In other words, i you imagine that you could shrink yourself down small enough to stand inside the cavity, then take out a tape measure and measure the distance across the cavity, from the surface of the outer-leaf drywall to the surface of the inner-leaf drywall: That's what you need to know. That's part of what controls the resonant frequency I was talking about above. The bigger that distance is, the lower the frequency is, and the better your isolation is. Assuming typical 2x4 stud framing for both leaves, and a 2" gap between the frames, that would give you a total cavity depth of 9": 3 1/2" for each stud depth, =7, plus the 2" gap between frames, = 9. (In your case, it would be a bit less since you will be "beefing up" the outer leaf with 2 layers of 5/8" drywall, so the cavity would be 1 1/4" less, or about 7 3/4"). That would probably be fine for your case, but it would be good to put some real numbers together here, and do the actual calculations, to make sure that it will do what you want it to do.

I want to build an airlock-type entry, ...

You can if you want, but you don't really need to. The normal way of dealing with doors in a 2-laf system like this, is simply to have a pair of doors back-to-back: one door in the inner leaf, and the other in the outer leaf. There's a thread about that here on the forum: site built door for high isolation That shows the usual way of doing that.

Of course, if you really wanted to have a "chamber" between the doors big enough to stand in, so you can close one door behind you before opening the other, then you can do that. Not a problem. In that case, you would just build out a closet-sized section of the wall, protruding into the room, and put the inner-leaf door on that. I can sketch that up for you roughly if you want, but not right now: It's nearly 3 AM where I am, and I need to get some sleep!

2. Can I use a standard solid-core metal exterior door as the exterior door (the outer leaf) while using a solid wood door for the inner leaf?

You can, yes. No problem. As long as you do what Starlight mentioned, and make sure that you have enough mass in each door, to match the mass of the wall ("surface density" is the more correct technical term here, but most people just talk about "mass"....)

3. For the beefing of the exterior wall, what's the best way to fasten the drywall to the OSB?

The best way is to NOT fasten it to the OSB! To maximize isolation, each layer in the leaf needs to be able to move independently, so it can flex and "wobble" by itself, but in conjunction with the other layers. If you screw them all firmly together, they they cannot act separately, and you lose a bit of isolation. So the method for "beefing up" that I mentioned above just has the drywall pressed up against the OSB, and held in place with small cleats that you nail sideways into the STUDS, not into the OSB. That way, the entire drywall panel is free to move any way it wants to. Of course, you do have to seal the edges air-tight, and that's what the caulk is for.

I saw the example in Rod's book of the caulk-in-place, but I'm not sure if that was the only thing holding the two drywall layers there.

The caulk, plus the cleats. I'll see if I can find some photos of how my clients have done that in the past, so you can see how it works in practice.

I think that's everything, although I'm sure I missed something.

The ceiling? Sound moves in all three dimensions, so your isolation plan must also be in three dimensions. Here too the existing roof of the garage is probably going to be your outer-leaf, so you might need to figure out how to beef that up the same as the outer-leaf wall, then you would build an inner-leaf ceiling that rests on top of the inner-leaf walls, to complete the system. One caveat here: roofs are often designed to be "ventilated deck", where air is supposed to come in under the eaves, flow past under the actual roof deck, then exit our through a ridge vent or gable end vents. If you have a roof done like that, you cannot use that as your outer-leaf, and you will need to build a "three-leaf" system up there. It's not as terrible as it sounds! If you can post some photos of your room, and especially of your roof, that would help to identify what you have, and figure out what the solution would be.

One more thing you might have missed here, is HVAC. I wrote an article about that a while back: why your studio needs HVAC. Take a look at that: it's rather important!


- Stuart -

[SoWhat]

Greetings Stuart,

Thanks for the quick (and massively detailed) reply.

I am grateful for the instructions on beefing up the exterior wall. It cleared up the confusion.

Sorry for leaving out some details. I knew I was likely to forget some. Here are the "corrections":

1. Right now, I'm waiting on permits for some demolition of an old existing structure on the property and then the concrete to be poured, then the prefab building will get done. I wanted to start my discussion here during this seemingly interminable process. Once the building goes up, I do a plethora of sound measurements.

2. The 12'6" height is from the bottom of the building to the highest point on the roof, which will indeed have the ventilated deck as you mentioned. I actually hadn't forgotten about the ceiling at all, but rather, forgot to put it in my post. Ugh. Was going to ask about the beefing up of the ceiling.

3. I meant the inner wall would have its studs staggered in relation to the exterior wall, not a staggered stud pattern within the wall itself.

4. Again, my haste is at fault for not discussing the HVAC: I'll be using a ductless multi split which I'll be sharing with my wife's art studio (separate building, but close enough to share one system). She won't be bothered by any sound from my studio as she's a former musician herself.

All the best,

Paul

[Soundman2020]

Source of the post 1. Right now, I'm waiting on permits for some demolition of an old existing structure on the property and then the concrete to be poured, then the prefab building will get done. I wanted to start my discussion here during this seemingly interminable process.

Great! So the building doesn't exist yet: that's good news, as it gives you more flexibility when the time comes, and you can do a better job of isolation. Are you going to erect it yourself, or will you get a company to put it up? I imagine the latter... If so, maybe you could have a chat with them in advance, letting them know that you plan to use it for a studio, and asking them to take some extra measures when they erect it to help you with that. They might want to charge you a bit more for that, but it might be money well spent. Basically, you want them to do an excellent job of sealing everything: Especially where the outer-walls rest on the slab. You'd be surprised how much sound can get out through tiny little gaps where the sole plates sit on the slab. Ask them to seal that with caulk. So just before the sit the walls down on the slab, run a couple of beads of good-quality caulk along where the sole plates will go. Ditto for where the walls meet each other: run a bead of caulk up the studs that butt up against each other, right as they are installing them. And the same for any other place where there might be gaps or cracks to the outside world.

Some other things you might want to consider: put in a small bathroom and kitchenette. If you are going to have musicians in there for long hours, you might not want them using your house bathroom and kitchen, so it's a good idea to have those inside the studio itself. Just partition off a small area outside of the actual studio area. Ditto for a storage area for road cases, guitar cases, mic stands, gear and instruments that are not being used, etc. Rather than have them cluttering up the actual rehearsal space, have a small storage room out where the bathroom/kitchenette area are.

2. The 12'6" height is from the bottom of the building to the highest point on the roof, which will indeed have the ventilated deck as you mentioned. I actually hadn't forgotten about the ceiling at all, but rather, forgot to put it in my post. Ugh. Was going to ask about the beefing up of the ceiling.

For that type of roof, what you'll need to do is to build a "middle leaf" ceiling up there some place, that completely seals off the vented roof area and has the same surface density as your outer-leaf walls. It's really your "outer leaf" ceiling, but side you also have a roof that is involved, it becomes your "middle leaf".

Now, if you are able to do so, instead of the typical garage roof truss that has joists running right across from wall top to wall top, specify that you want a "raised tie" or "collar tie" truss, where that cross bracing is placed higher up, so you can put your middle-leaf on that, and still leave plenty of height internally for the actual studio. Here's an example:

Once again, they might charge you extra for switching to a different type of truss, but it is well worthwhile, as it allows you to have a higher final internal ceiling height, which is great for acoustics, and also great visually.

3. I meant the inner wall would have its studs staggered in relation to the exterior wall, not a staggered stud pattern within the wall itself.

Ahhh! OK.

4. Again, my haste is at fault for not discussing the HVAC: I'll be using a ductless multi split which I'll be sharing with my wife's art studio (separate building, but close enough to share one system). She won't be bothered by any sound from my studio as she's a former musician herself.

Great! That takes care of three of the four letters in HVAC: It deals with "heating" and the "air conditioning", but you still need to do the "ventilation" part. Mini-split systems do not provide any ventilation: all the do is circulate the air that is already inside the room, so you still need to plan for the ventilation: how to bring in fresh air, and exhaust the stale air.

I'm looking forward to seeing how the pre-fab building comes together, and also your design for the interior!

- Stuart -

[SoWhat]

Greetings Stuart,

Once again, thank you!

I had to chuckle when you wrote, "Great! So the building doesn't exist yet: that's good news." I have that sort of sense of humor. I love syntax issues.

First things first. Ack! Why I didn't mention the ERV for fresh air is simply beyond me. It was at the top of my list. Given Philly's summer humidity levels, methinks it's the best choice to pair with the mini split. I've been in touch with a reputable, well-reviewed HVAC company here in Philly.

As far as the toilet/kitchen idea goes, any of the musicians who would be coming here are people who've been in my house already. Besides, the thought of adding plumbing (i.e. new main drain and connection to the septic system) to this project makes my head hurt. On the storage front, I'm pretty sure I can work that into the final plan.

I will certainly ask if the company that's doing the build will do all the sealing as you suggested. I was going to add the caulk to all of those seams, but there would have been no way to do the plates. Since I will be up to my eyeballs in caulk with the beefing of the exterior walls and ceiling, I think I'll pay to have someone else do the first bit, if it's an option.

I will have to check if they offer a choice in trusses. (Fifty years ago, that sentence would have had a much different meaning.) If they do, I will use your suggestion. If they don't, what's my alternative?

While I get myself up to speed with SketchUp, I will draw out a (very) preliminary floor plan the old fashioned way and post.

Again, my thanks for your time and expertise!

All the best,

Paul

[Marius]

Paul,

Hello from San Antonio Texas. Can you pass along the name of your HVAC guy please?

I am shopping for quiet mini split units. Also shopping for good ERV unit with dehumidifier.

Marius Perron

[SoWhat]

Greetings Marius,

I am in Philly, and the place I'm using is a local business here. Their out-of-state service areas are only in New Jersey and Delaware. I would suggest searching for HVAC company reviews for San Antonio. Once you've found some highly recommended ones, then you can see if they do mini splits. From my research, I can tell you that if you're going to use Mitsubishi (which I am), you should go through one of their "Diamond" dealers/installers. While you can get the units from a variety of sources, working with these preferred dealers activate a much longer warranty. Strangely enough, the company that I'm using here recommended shopping for my ERV elsewhere, as they don't have smaller units at a good price. I am certainly appreciative of their honesty. I hope this helps.

BTW, Jesse James & GGBR was a band I played with when Jesse and I both lived in Idaho. He now lives in SA. He's quite a good player, so you might want to check him out.

All the best,

Paul

[Marius]

Thank you , Paul.
I have been playing in bands in San Antonio since the 70's. I run a school and recording studio: https://www.audio-eng.com/ Am in the design stages of a new place.

Never ran into Jesse James. What is his real name?

[SoWhat]

Jesse James Burnitt. He's probably been there about three years now.

[Soundman2020]

Source of the post First things first. Ack! Why I didn't mention the ERV for fresh air is simply beyond me. It was at the top of my list. Given Philly's summer humidity levels, methinks it's the best choice to pair with the mini split. I've been in touch with a reputable, well-reviewed HVAC company here in Philly.

Well, that takes care of the air movement itself, as well as heating, cooling, dehumidify, and energy recovery, but don't forget about your ducts and silencers! Getting those right is rather important for studios, and often overlooked. Think of it this way: to get the right amount of air into and out of each room in the studio, you need to chop huge gigantic holes in your carefully built and sealed isolation shell... thus destroying your isolation! Silencer boxes (sometimes also called "baffle boxes") are what you need to accomplish that. Typical HVAC contractors will want to talk about commercial off-the-shelf silencers that go in line with the ducts, but they don't cut it at all for studios: not nearly up to the task. Those are good for reducing typical office sounds in the ducts, as well as HVAC air noise and equipment noise, but won't do a lot when you have Gus the Gorilla on drums in the live room, along with Big Bad Bob the Bassist, who likes to stack bass cabs to the ceiling and turn them to eleven... You need a somewhat more substantial silencer for dealing with that. Ditto for control rooms: Perhaps to a lesser extent, but still necessary. The HVAC systems in typical offices, shops, schools and homes don't have full-spectrum 85 dBC most of the day, that gets pushed over 100 every now and then to "check the bass"... those shiny silver commercial silencers are out of their league.

Ditto when it comes to ducts: house HVAC systems typically move a small volume of air at high speeds to ventilate, but that's the exact opposite of what a studio needs: you want a large volume of air moving at very low speed. Why? Because when you have air moving at even moderate speeds, it creates noise all by itself. Because of turbulence. The air moving inside the ducts only flows smoothly and quietly for long, straight smooth runs of duct: as soon as you put in a curve, damper, VAV, or register, the air flow breaks up into turbulence, which is noisy: everything from "rumble" to "hiss" is in there. The faster the air is moving, the more turbulence you get, so the louder the noise is... and you don't want loud rumbling hissy noises in your studio! Fatal if that gets into every track you lay down in your LR, and annoying when you are trying to mix in the CR. So you need to get the speed down below 300 fpm at the register (200 is even better), but that means you have to move a larger volume of air to get the right flow. Large volume implies large diameter ducts. Traditional HVAC people want small ducts and registers, not large ones that studios need.

So take that into account when you start designing your HVAC system. Silencers are big: they take up a lot of space. They are heavy, too. So you need to think about how you will mount them.

Here are a couple of current threads here on the forum that get into the issue of silencers in studios: Small studio with high isolation: how to build one. viewtopic.php?t=81 You have probably ready seen those, but take a closer look at how they are doing their silencers. You can get ideas from that, to help design yours.

Besides, the thought of adding plumbing (i.e. new main drain and connection to the septic system) to this project makes my head hurt.

You could hire a plumber to do that for you: costs a bit more, but takes the pain out of it. Take a look at Tom's thread, to see how he is handling that. The reason I suggest having a bathroom and kitchenette in the studio, even if all your musicians are friend you don't mind having in your house, also has to do with the weather: Talking a walk through rain, snow, cold, wind, heat, etc. just to get a cup of coffee, warm up a pizza, or take a leak, is not an attractive option at some times of year! Having the facilities available right there, in the studio, is a better option. Of course, it does add extra cost! So if you are on a very tight budget, then you might have to leave it out, but if you can stretch the budget, it's worth thinking about.

Since I will be up to my eyeballs in caulk with the beefing of the exterior walls and ceiling, I think I'll pay to have someone else do the first bit, if it's an option.

Right! More hands on deck can really help to make things go faster, especially with the pre-fab guys just wanted to unload the truck, slap things in place, and get out of there fast. So it's good to give them a heads-up that you'll have people there to squirt down the caulk beads under the sole plates: they'll need to take that into account in their timing. And do yourself a big favor here; get a compressor and pneumatic caulking guns for this! It goes way faster, and the result is better and cleaner. Save your hands... squeezing a manual caulking gun all day will wreck your wrists! Renting a compressor and buying some hoses and a couple of guns is well worth the investment. Or even buy your own compressor, then sell it again when you have completed the studio to recover most of the money You'll find LOTS of uses for a compressor while building a studio...

I will have to check if they offer a choice in trusses. If they do, I will use your suggestion. If they don't, what's my alternative?

If all you get is standard trusses with lower chord joists at wall-top height, then you really only have two choices: 1) raise the ties yourself, turning them into raised-tie trusses ( a big job, but it can be done: I have photos form clients who have done that, if you are interested): 2) Live with it, and end up with a low inner-leaf ceiling.

With option 2, you would just put up OSB and drywall on the bottom edge of the truss joists, and that would become your "middle leaf", then build your inner-leaf ceiling under that, resting on top of the inner-leaf walls. The issue here is that the truss joists might not be beefy enough to carry the load you need to put on the, if you need high isolation. The mass (surface density) on that "middle-leaf" ceiling would need to be similar to the mass of the outer-leaf walls, to get reasonable isolation. In theory, a three-leaf system gives the best isolation when the mass on the middle leaf is the same as BOTH the outer leaf AND the inner leaf combined! So for high isolation, you need a lot of mass on that middle-leaf.... probably more than the typical pre-fab garage truss can handle. So you would likely need to beef up those trusses yourself in any case, by sistering the joists to larger dimension lumber, or adding additional joists in between the truss joists... or both.

If you do go for option #2, then your inner-leaf ceiling is going to be lower than the wall tops, and thus lower than a typical garage ceiling. Low ceilings are not so good for studios: a low ceiling tends to give the room a sort of "boxy" sound, and generally musicians do not like playing in rooms with low ceilings: they don't get the "spacious" feel of the instruments that comes from higher ceilings.

To maximize your inner-leaf ceiling height, you could build it "inside out", like this: What is an "inside-out ceiling"? Do you need one? How do you build one? That would be your best bet, if you are stuck with option #2.

While I get myself up to speed with SketchUp, I will draw out a (very) preliminary floor plan the old fashioned way and post.

- Stuart -

[Marius]

Stuart –
About the HVAC Ducts and Silencers…

If Paul (and myself) are doing Mini-Splits – we do not need Ducts and Silencers for that – correct?

But we do need Ducts and Silencers for the fresh air (ERV) unit – right?

And… do we need two for the ERV - one for the duct of the fresh air coming in and one for the stale air going out – right?

And it seems to me that the ERV would not be moving as much air as a typical conventional AC system – so perhaps those ducts could be smaller… we wouldn’t need to:
“chop huge gigantic holes in your carefully built and sealed isolation shell.”

[SoWhat]

Greetings Stuart,

Once again, thanks very much indeed!

Yes, I've been spending the better part of this week reading about baffle boxes, and that's after having read quite a bit before. A big job indeed. Luckily, my contractor is an amazing fabricator (read: fast AND accurate), so I'll have him cut the pieces and I'll assemble. He will be doing the "inside room" (along with my drywall guy and electrician). He's had experience building home theatre rooms (including some that he KNEW weren't right acoustically), but "the client wants what the client wants," right? He just bought Rod's book to prepare for this project. I will, of course, direct him to this thread (among others I've found useful during my research). I'm somewhat handy so I will be helping as much as possible to save on labor cost.

I will wrestle with the ceiling issue as I wait impatiently for the demolition permit to go through. We are having an in-ground swimming pool removed. Then I will have more time to wait for the next permits: the concrete slabs and my building and my wife's building. I think I can sort it out by then. Yes, the low ceiling thing is terrible. I'm contacting the shed company about the trusses Monday.

I do think the plumbing thing will be impossible, but an in-studio snack area with the appropriate appliances was going to be part of the plan anyway. Even in lousy weather, the walk to the house for the toilet is only going to be 20 feet at most. Perhaps a composting toilet outside...

Thanks again.

All the best,

Paul

[SoWhat]

Greetings Marius,

Just saw your post. I believe it's two and two.

Or, we all call move our projects into tents in open fields...Isolation, Schmisolation!

All the best,

Paul