garage studio construction underway - on the right track?

Hi all- I can't believe that I only found this forum on the day I began construction on my garage studio a week ago! After almost 3 years of thinking, planning, and research, I finally found a gold mine here, but haven't had time to pore over it all because we're heavy into building. Fromt the site here, I heard about Rod's book and promptly downloaded it and spent some long nights after long days trying to speedread some chapters. I'm in Oakland, across the bay from San Francisco, in Northern California. I am rebuilding my delapidated garage to use as a combo of sound gear workshop (I record production sound for film & TV) and music studio. I imagine it to be a space wherein I will play and record, so most of the time it will be one instrument at a time, including acoustic and electric guitar, electric bass and sometimes some percussion or drums. I'm also entertaining the possibility of recording some ensembles in there. I could imagine reaching levels of 90-100 dB inside the room with a band in there, so I am planning as much isolation as I can. As you will read, I am also making some sacrifices for the fact that it is also a workshop (ie, not full-time music studio), which I have noted clearly in the details below. It's worth mentioning that I have neighbors behind the garage and to one side of the garage, both about 20+ feet away. And my house is 7' from the other side wall. Also, the street is 12' from the front doors. So I'm hoping isolation will be robust enough to not bother the neighbors during reasonable playing hours. I'm currently around $5000 USD into it, with the exterior walls and stucco complete, and the materials for the interior wall construction in hand. I had no firm budget, but imagined it could run as high as $10,000. Let's say I'd like to come in under that... In a nutshell, I will follow the room-in-a-room construction, using double wall method, with separate bottom and top plates. Here's a pictographic look at the details. They show some of the design elements, but not all. Once construction began, I ran out of time to play with Sketchup. Here are the details written out: Building Entire building (exterior) - 19' x 10' x 11'. To accommodate my family's needs for a utility space, I will leave 4 feet from the garage doors, then build the interior frame, with another door, so it reduces the size of the interior room. Also, leaving garage doors is a sacrifice (see below under doors) Floor - concrete slab. Considering additional wood flooring in interior room, but that will be down the line. Foundation - 3' high. Mostly oncrete with a cement cap. Interior room – 14'8" x 9' x ~8.5' high Exterior wall - 3/4" stucco over 3/4" sheathing or CDX plywood. 2 x 4 x 8' frame, 24" O.C., on a 3 foot cement foundation Interior wall - 2x4 x 8.5' SIDEWAYS, 16" O.C., with double layer of 5/8" fire-rated drywall. Exterior roof - Torchdown roof over 3/4" CDX plywood, on a 2x6 rafter frame. Floor - SACRIFICE #1 - !!!!!!! Opening Skylight - 22-1/2" x 34-1/2" !!!!!!! The skylight will allow natural light in, and will accommodate the need for ventilation in the interior room. For louder music, I have planned to make a plug for the opening of the skylight into the interior room, so I can block it off when necessary. A compromise, I know, but it will feel good. Interior roof ceiling - double layer of 5/8" fire-rated drywall Insulation I will seal the exterior sheathing/plywood with GE Silicone II and backer rod where it fits. Ultratouch R-19 3-1/2" deep nestled between exterior wall studs. Ultratouch R-19 5-1/2" deep between ceiling rafters Air gaps: between the sloped roof and the interior ceiling, air gap will range from ~1" to 1'. For the ext and int walls, about 2" of air between the insulation and the interior studs. Doors Exterior (street side) - SACRIFICE #2 - Two 4 x 8 garage doors. Plan to make these with 2x4 and lined with R-19 Ultratouch. They will close onto a plastic or rubber tube stripping over 2"x2" doorstops. to seal them as best as I can. Exterior (backyard) - 30" x 76" door on 2 x 4 frame filled with either R-19 Ultratouch or sand. Also considering simply a solid core door. Will close onto a 2"x2" doorstop with stripping. Utility space to Int room - Not yet designed, but probably 30" x 76", solid core, or sand filled. From a functional viewpoint, my ideal would be a sliding door, like a pocket door that goes into the wall, to save "swing" space, but that might compromise isolation somehow. Can't be sliding glass for security reasons. Exterior backyard to Int room - I have to descend 3 or 4 steps, so I'm planning to enclose those stairs to make a sound lock, and put another door at the bottom of the stairs. Again, roughly 30" x 76" solid core or sand-filled. Electrical 2 circuits coming through ext wall via one 1" rigid conduit (sealed with construction sealant and stucco). On exterior frame, a single junction box will distribute to a total of 4 plugs. Lights will be on one of the circuits. Probably planning to use externally mounted outlet boxes, so I just poke through the wall with Romex, and then seal it with GE Silicone II. Other ideas are welcome. Also considering poking through the stucco to run an 8-channel snake underground into my house, so I could record from the house, with the band playing in the studio space. My questions are these: 1) because the interior wall will be framed using two by fours turned sideways, I was thinking to send a nail into the foundation to help with structural integrity. Is it a serious compromise to the isolation of my double wall construction to nail the interior wall into the foundation? (While writing this, I thought maybe I could nail every 3rd or 4th stud to reduce the number of connections between the int wall and the foundation. (SEE ATTACHMENT) 2) Also relating to the interior wall frame: I have 5.5" between the ext plywood and the int studs. Should I stick to having 2" of air to the studs (3.5" to the back of the interior drywall)? OR, could I consider putting in 5.5" R-19 insulation which would touch the back of the interior studs in some places, leaving about 1.5" of air between the int wall drywall and the insulation? 3) Against my will, I know I must ventilate the small attic area, so I will probably drill 1-1/2" holes into several of the eaves on the right side. Must the air be able to pass along the interior surface of the roof? Or can I stuff the ultratouch all the way up to the deck? Are there other measures I can take to ventilate the roof ("attic") without punching more holes in my exterior wall?! Somewhere here I read about using a vapor barrier on the outside of the interior room, to prevent the moisture from the studio space (where the people and machines are) from reaching the attic. Is that a recommended approach? 4) What can anyone recommend for a good sealing liner for the doors? Rubber or plastic tubing? 5) Has anyone had any success implementing a sliding door that maintains some form of isolation? 6) This is a completely subjective question, but.... Based on my proximity to neighbors, my isolation desires, and my compromises, is it worth the time and expense to put a piece of 5/8" drywall (and backer rod/sealant) on the inside of the ext wall to beef up that leaf? This would work hand-in-hand with Question 2 above: by adding a 5/8" drywall, I would definitely go with the reduced 3.5" insulation. What's the trade-off? I am still deliberating over ventilation needs in the interior room, but I am considering a baffled insulated box system with a low-velocity fan to bring in some fresh air. It would be royal to hear back before I continue with the interior construction in a few days, so I don't have to back-track if I've really goofed something up! Thanks a million, Brian Copenhagen

Hi Brian, and welcome to the forum! :)

I can't believe that I only found this forum on the day I began construction on my garage studio

Better late than never! Fortunately you are still at the stage where the problems can be fixed, without oo much hassle or expense. It would have been much sadder if you would have found us the day you FINISHED your studio, instead of the day you STARTED!! :)

including acoustic and electric guitar, electric bass and sometimes some percussion or drums

You mean acoustic percussion and acoustic drums? Or electronic? I imagine acoustic...

I could imagine reaching levels of 90-100 dB inside the room with a band in there,

That's more than just a little bit on the low side. The levels will be substantially more than that: Drums alone are more like 110 to 115. A full band can get close to 120 ("C" weighted, slow response).

It's worth mentioning that I have neighbors behind the garage and to one side of the garage, both about 20+ feet away. And my house is 7' from the other side wall. Also, the street is 12' from the front doors. So I'm hoping isolation will be robust enough to not bother the neighbors during reasonable playing hours.

It's actually worse than that: there are legal limits on how loud you can be, regardless of what you think is acceptable for the neighbors, so you should really get a copy of the noise regulations from your local municipality, and build to isolate enough that you don't go past level.

In a nutshell, I will follow the room-in-a-room construction, using double wall method, with separate bottom and top plates.

Maybe it's just a terminology thing, but there's no way you can separate the top plates from the bottom plates! The bottom plates are the 2x4s laid flat on the floor, on which your studs rest, and the top plates are the 2x4s laid flat across the tops of the studs, on which the ceiling rests. They are structural members, so it is not possible to separate them: they both must be firmly attached to the actual studs. But I think you might have been talking about something else? Not "plates" in the normal construction sense?

They show some of the design elements, but not all. Once construction began, I ran out of time to play with Sketchup.

You might want to roll back a bit on that: It is pretty much always a mistake to start building before your design is complete.

Floor - concrete slab. Considering additional wood flooring in interior room, but that will be down the line.

Why? Concrete is an excellent floor, acoustically, and you are also tight on room height. Putting anything more than simple laminate flooring or ceramic tiles is going to eat into your ceiling height.

Exterior wall - 3/4" stucco over 3/4" sheathing or CDX plywood.

Good. Makes for a decent outer-leaf.

Interior wall - 2x4 x 8.5' SIDEWAYS,

Sideways? Does code allow that? In California? I'm surprised if it does: are you sure your inspector has OK'd that? With all the seismic regulations on CA, I would not have thought they would allow structural framing to be turned edgewise.

with double layer of 5/8" fire-rated drywall.

I would seriously suggest replacing the first layer with 5/8" OSB or structural plywood. Especially with studs sideways!

Exterior roof - Torchdown roof over 3/4" CDX plywood, on a 2x6 rafter frame.

That's a potential weak point. Compared to the walls and floor, you have a lot less mass up there.

SACRIFICE #1 - !!!!!!! Opening Skylight - 22-1/2" x 34-1/2" !!!!!!!

OK, this might seem like a real harsh question, but if you are going to have an operable skylight, then why are you bothering to build an inner-leaf "room-in-a-room" isolation system? There simply is no point. The operable skylight destroys any benefit you would have gotten from the two-leaf design. Sorry to say. If the skylight is going to stay, then save your self a lot of many and scrap the room-in-a-room concept, and also scrap the idea of being able to record drums and hold jamming sessions without disturbing your neighbors. You could have a skylight, yes, but not one that opens. That makes no sense.

and will accommodate the need for ventilation in the interior room.

Actually, it wont. For a studio, you need constant ventilation, all the time the room is occupied. Instruments, equipment, microphones and even people suffer from changing temperature and humidity in a studio: Tones change, tuning changes, necessity changes... If you rely on opening and closing the skylight every few minutes to "ventilate", then you'll have constant ups and downs in instrument tones, microphone tones, and even vocal tones, due to the wild swings in humidity and temperature. It just isn't a realistic, practical solution. Read the chapter in Rod's book on HVAC. It's an eye-opener.

For louder music, I have planned to make a plug for the opening of the skylight into the interior room, so I can block it off when necessary. A compromise, I know, but it will feel good.

Actually, it won't feel very good at all! It's just not a realistic approach. The room will be double-sealed, hermetically air-tight, twice over, and wrapped with multiple layers of very efficient thermal insulation. To get an idea of how good it will feel, take a sleeping bag, get inside, get someone to wrap it with thick plastic sheeting, sealed with duct tape, put that inside another sleeping bag, then wrap it in plastic again. And seal it. That's about how good it will feel... :) (OK, don't actually do that with the sleeping bags!!!! That's just to illustrate the point with a mental picture...) Proper HVAC is generally the most forgotten part of studio building, as people simply do not appreciate the importance. It is a major part of the studio: without it, you don't have a usable studio. It's that simple. You need a proper ventilation system, with fans, ducts and silencer boxes, correctly dimensions to move the right amount of air through the room, a the right speed, and you need an air conditioner to cool and dehumidify the air correctly: These are not luxuries in s studio: they are basic necessities, just as much as electricity and furniture.

Interior roof ceiling - double layer of 5/8" fire-rated drywall

You didn't mention how that is to be hung: I imagine you are planning on 2x6 or 2x8 joists across the tops of the inner-leaf walls?

Air gaps: between the sloped roof and the interior ceiling, air gap will range from ~1" to 1'. For the ext and int walls, about 2" of air between the insulation and the interior studs.

You seem to be misunderstanding the term "air gap". In isolation, the "air gap" is the distance between the surface of the outer-leaf mass and the surface of the inner-leaf mass, regardless of any framing or insulation. The air gap might have insulation in it, and might even be 100% filled with insulation, but it is still the air gap, for purposes of acoustic calculations. (In fact, theoretically (and paradoxically), the air gap gets bigger as you put more insulation in it.... :) ) You need a minimum of 4 inches of air gap, never less than that. And seeing that you want to isolate drums in a residential neighborhood, you are going to need more than 4" to stay legal. Probably more like 6 or 8.

Two 4 x 8 garage doors. Plan to make these with 2x4 and lined with R-19 Ultratouch.

Once again, if you are going that route, then why bother doing the inner leaf at all? Those doors are a major problem for isolation. Paired doors that close against each other, with no central jamb, are notoriously hard to seal. How do you plan to get the same mass on them as with the walls? Multiple layers of MDF, screwed and glued? Lead sheeting? Regardless of what the plan is, those doors are going to be massively heavy, and your framing does not show the type of structural support that you need to do that. Those will need some pretty major members and very heavy duty hinges. I would guess they will weigh a few hundred pounds each...

They will close onto a plastic or rubber tube stripping over 2"x2" doorstops. to seal them as best as I can.

Go with proper acoustic seals. Take a look at the Zero International catalog: I'm sure they have something for that situation. The are among the best in the business, but even then I would not count on getting a good seal.

Exterior (backyard) - 30" x 76" door on 2 x 4 frame filled with either R-19 Ultratouch or sand.

"Filled"? That sounds like you are planning in using hollow-core doors. That simply isn't an option, especially if you plan to fill them with sand. There is a design for sand-filled doors, but not based on plain old hollow-core blanks. And frankly, if you have an operable skylight and operable garage doors, then why bother going to all that trouble to beef up this door at the back? Take a look at the chapter on doors and windows in Rod's book. He lays out two good methods for doing it right. His "superdoor" would probably work for you, assuming that you solve the issue of the skylight and the operable garage doors.

From a functional viewpoint, my ideal would be a sliding door, like a pocket door that goes into the wall, to save "swing" space, but that might compromise isolation somehow.

Yes it would. Over the years, the idea of pocket doors for studios pops up every now and then, but I have never seen anyone manage to actually implement one successfully. I even tried to design one myself a few years ago, but had to give up in the end: there just isn't any realistic way of doing it.

2 circuits coming through ext wall via one 1" rigid conduit (sealed with construction sealant and stucco).

THere needs to be a mechanical break in the conduit between the outer.leaf and inner-leaf. Just cut out s shirt section, maybe an inch or so long, and wrap it with rubber sheeting, held in place with hose clamps. That is to decouple the flanking path created by the conduit.

On exterior frame, a single junction box will distribute to a total of 4 plugs.

I think you meant to write "On inner frame". The electrical panel has to be on the inner-leaf, not the outer leaf, in order to meet thre "only one penetration" guideline.

Probably planning to use externally mounted outlet boxes, so I just poke through the wall with Romex, and then seal it with GE Silicone II. Other ideas are welcome.

The normal method is to not make any holes at all your inner-leaf mass, since that compromises isolation greatly. So you have just that one single penetration where the main feed crosses over from outer-leaf to inner-leaf, then do all the distribution from that panel, using surface-mount flat ducts, surface mount switches, surface mount plugs, surface mount light fittings, etc. Nothing should ever penetrate the inner-leaf.

Also considering poking through the stucco to run an 8-channel snake underground into my house, so I could record from the house, with the band playing in the studio space.

That has to go through conduit, done the same way as the power feed, and duly sealed at each end.

1) because the interior wall will be framed using two by fours turned sideways, I was thinking to send a nail into the foundation to help with structural integrity.

Once again, I'm not even convinced that building code allows "sideways stud construction", and even if it does, I would never do that in an earthquake zone. I'm well aware of how things move in a major quake, and I would certainly not stand inside a room I knew to have been built like that. Where I live, that would not pass inspection. I'm very surprised that it can pass in California. And no, it would be a bad idea to nail your inner-leaf studs to your outer-leaf foundation, from the isolation point of view. The entire point of "room-in-a-room" construction is that the inner "room" is totally independent of the outer room: they CANNOT touch anywhere, not even a single nail. They MUST be built as completely separate framing systems, not attached to each other at all. Your photo shows the inner-leaf "sideways" stud touching the concrete: that cannot happen. You need a decent gap there, to ensure that they never can touch, ever: The two rooms are fully decoupled, totally separate, entirely isolated.

Is it a serious compromise to the isolation of my double wall construction to nail the interior wall into the foundation?

Yes. Worse than "serious compromise to the isolation", it actually negates everything you are trying to do. Your isolation from a wall built like that would be even less than for a normal house wall.

2) Also relating to the interior wall frame: I have 5.5" between the ext plywood and the int studs. Should I stick to having 2" of air to the studs (3.5" to the back of the interior drywall)? OR, could I consider putting in 5.5" R-19 insulation which would touch the back of the interior studs in some places, leaving about 1.5" of air between the int wall drywall and the insulation?

I already covered this above, I think: the air gap is the distance across the interior wall cavity, between the surface of the outer leaf mass and the surface of the inner leaf mass, regardless of whether or not there is insulation in there. Insulation is mostly air anyway... Your air gap needs to be at least 4 inches on all sides, and for your case, probably 6 or 8 would be more reasonable. So you might as well turn the studs to the correct orientation, leave a 1" gap between the frames, and you already have 8 inches of air. That's plenty.

3) Against my will, I know I must ventilate the small attic area,

Right! If you want your roof and ceiling to survive for more than a couple of seasons, that's an absolute necessity.

so I will probably drill 1-1/2" holes into several of the eaves on the right side.

Ummm.... you'll need more than that: I would suggest full-length eave vents along both sides. But this brings up the next major issue, and it's a biggie: Since those holes destroy any isolation you would have got from the roof as an outer-leaf, you are left with no choice but to build a three-leaf ceiling system, with all the negatives that this implies...

Must the air be able to pass along the interior surface of the roof?

Yes.

Or can I stuff the ultratouch all the way up to the deck?

No.

Somewhere here I read about using a vapor barrier on the outside of the interior room, to prevent the moisture from the studio space (where the people and machines are) from reaching the attic. Is that a recommended approach?

Code very likely requires a vapor barrier somewhere. It should specify where that has to go. Ask your inspector what code requires, and follow his advice.

4) What can anyone recommend for a good sealing liner for the doors? Rubber or plastic tubing?

Proper acoustic isolation seals are what you need, at least two of them, around the full perimeter of each door, and probably three. Make the last one magnetic, to help keep the door closed, since you cannot use any mechanical latches, as they require drilling holes trough the door, and of course, you can't do that.

5) Has anyone had any success implementing a sliding door that maintains some form of isolation?

Sliding door? Yes. John does it all the time with his studios. Pocket door? No. None that I'm aware of.

6) This is a completely subjective question, but.... Based on my proximity to neighbors, my isolation desires, and my compromises, is it worth the time and expense to put a piece of 5/8" drywall (and backer rod/sealant) on the inside of the ext wall to beef up that leaf

?If the outer leaf is 3/4" stucco over 3/4" OSB or ply, then you have a lot of mass in that already. Not much benefit from doing that.

I am still deliberating over ventilation needs in the interior room, but I am considering a baffled insulated box system with a low-velocity fan to bring in some fresh air

Yes! Definitely! And another silencer box to exhaust the stale air to the outside again. I hope I haven't discouraged you too much! But I'm sure you didn't come here just wanting to hear about what you are doing right... :) There's a lot you are doing right! But there's also several things you are doing wrong that make no sense if you hope to have the type of isolation you are talking about. But if you fix the above, then you stand a good chance of getting where you want to go. - Stuart -

You mean acoustic percussion and acoustic drums? Or electronic? I imagine acoustic...

Acoustic percussion and drums.

The levels will be substantially more than that: Drums alone are more like 110 to 115. A full band can get close to 120 ("C" weighted, slow response).

Duly noted.

there are legal limits on how loud you can be,...so you should really get a copy of the noise regulations from your local municipality, and build to isolate enough that you don't go past level

55dB at the property line until 9pm. I've been through the ringer over this issue with a previous rehearsal space.

...separate bottom and top plates.

Maybe it's just a terminology thing, but there's no way you can separate the top plates from the bottom plates!

Yes, I think it's a terminology thing… I mean that the plates for the exterior wall are separate from the plates for the interior wall... As opposed to shared plates, as in a staggered wall construction.

I ran out of time to play with Sketchup.

You might want to roll back a bit on that: It is pretty much always a mistake to start building before your design is complete.

Also duly noted. I have made the plans, just didn't get everything into Sketchup.

Floor - concrete slab. Considering additional wood flooring in interior room, but that will be down the line.

Why? Concrete is an excellent floor, acoustically, and you are also tight on room height. Putting anything more than simple laminate flooring or ceramic tiles is going to eat into your ceiling height.

Fantastic. If I did anything more than concrete, you guessed it, simple laminate on a vapor barrier and a thin pad.

Interior wall - 2x4 x 8.5' SIDEWAYS,

Sideways? Does code allow that? In California? I'm surprised if it does: are you sure your inspector has OK'd that? With all the seismic regulations on CA, I would not have thought they would allow structural framing to be turned edgewise.

Because my property is on a corner with a smallish lot for the area, there are numerous reasons that inspectors are not involved with this re-build. But I'm hearing your structural advice loud and clear. More on this below, with regard to the idea of nailing into the foundation wall.

I would seriously suggest replacing the first layer with 5/8" OSB or structural plywood. Especially with studs sideways!

So a layer of 5/8" plywood, and one layer of 5/8" drywall. I understand the plywood being better for shearing the wall, but would it be a lesser layer than using 2x drywall in the inner-leaf.

Exterior roof - Torchdown roof over 3/4" CDX plywood, on a 2x6 rafter frame.

That's a potential weak point. Compared to the walls and floor, you have a lot less mass up there.

Hmm. I could beef up the roof with 5/8" drywall between the rafters.

SACRIFICE #1 - !!!!!!! Opening Skylight - 22-1/2" x 34-1/2" !!!!!!!

You could have a skylight, yes, but not one that opens. That makes no sense.

Understood. As I said, this is a sacrifice I decided to make. Since it's not a 100% recording studio, I have gone with an opening skylight. I don't have the knowledge you do, but it's hard for me to believe that building out the inner leaf will all be for naught just because I have a skylight. It's a 3-paned window with a watertight seal, so it must have SOME effect on reducing sound.

Read the chapter in Rod's book on HVAC. It's an eye-opener.

I did read that chapter, and indeed it is quite enlightening on how much heat and moisture machines and people put out. One idea he proposes for his Through-the-Wall AC is to temporarily plug where the AC penetrates. And I was basing my idea for the skylight plug on his notion that plugging is "one manner of dealing with the penetration and still maintaining isolation. This is also a very effective isolation system for windows in general."

Proper HVAC is generally the most forgotten part of studio building, as people simply do not appreciate the importance. It is a major part of the studio: without it, you don't have a usable studio. It's that simple. You need a proper ventilation system, with fans, ducts and silencer boxes, correctly dimensions to move the right amount of air through the room, a the right speed, and you need an air conditioner to cool and dehumidify the air correctly: These are not luxuries in s studio: they are basic necessities, just as much as electricity and furniture.

I will definitely put in ventilation...

Interior roof ceiling - double layer of 5/8" fire-rated drywall

You didn't mention how that is to be hung: I imagine you are planning on 2x6 or 2x8 joists across the tops of the inner-leaf walls?

I was planning 2x4s (on edge). It may sound too weak, but with 16 OC rafters, and only 14' x 9', I think it will hold up.

Air gaps

You seem to be misunderstanding the term "air gap". In isolation, the "air gap" is the distance between the surface of the outer-leaf mass and the surface of the inner-leaf mass, regardless of any framing or insulation. The air gap might have insulation in it, and might even be 100% filled with insulation, but it is still the air gap, for purposes of acoustic calculations

Great! Thank you for the clarification.

Two 4 x 8 garage doors

Those doors are a major problem for isolation. Paired doors that close against each other, with no central jamb, are notoriously hard to seal.

This is definitely not a done deal. I won't ever need to drive a vehicle in, so I'm also considering to just frame a wall there with a "man" door so I can better reinforce and isolate in order to reduce the compromise of trying to seal the two big garage doors. Thanks for that.

Go with proper acoustic seals. Take a look at the Zero International catalog

Will check it out.

Exterior (backyard) - 30" x 76" door

Take a look at the chapter on doors and windows in Rod's book. He lays out two good methods for doing it right. His "superdoor" would probably work for you

Will do.

2 circuits coming through ext wall via one 1" rigid conduit (sealed with construction sealant and stucco).

THere needs to be a mechanical break in the conduit between the outer.leaf and inner-leaf. Just cut out s shirt section, maybe an inch or so long, and wrap it with rubber sheeting, held in place with hose clamps. That is to decouple the flanking path created by the conduit.

Just to clarify: the conduit comes thru the outer leaf (stucco and ply), straight into a box that is screwed onto the outer leaf framing. So the rigid conduit never touches the inner leaf.

The normal method is to not make any holes at all your inner-leaf mass, since that compromises isolation greatly. So you have just that one single penetration where the main feed crosses over from outer-leaf to inner-leaf, then do all the distribution from that panel, using surface-mount flat ducts, surface mount switches, surface mount plugs, surface mount light fittings, etc. Nothing should ever penetrate the inner-leaf.

Good ideas.

1) because the interior wall will be framed using two by fours turned sideways, I was thinking to send a nail into the foundation to help with structural integrity.

Worse than "serious compromise to the isolation", it actually negates everything you are trying to do. Your isolation from a wall built like that would be even less than for a normal house wall.

In my way of rationalizing it, naive though it may be, I am thinking that nailing the inner leaf to the foundation would create a scenario more like a staggered stud construction instead of a double wall room-in-room. Instead of sharing the bottom and top plates, as in staggered stud, it would share the foundation. Is the concrete foundation better at isolating a flanking path than the top/bottom plates are in a staggered stud config? As for the flat-framed inner leaf, I'm definitely reconsidering decoupling from the foundation (not nailing too it), in order to frame the 2x4s properly and losing the few more inches of valuable floor space. But if I stick to flat-framing anyway, I am thinking to put blocking in between the studs for more structural integrity.

3) Against my will, I know I must ventilate the small attic area,

Right! If you want your roof and ceiling to survive for more than a couple of seasons, that's an absolute necessity.

so I will probably drill 1-1/2" holes into several of the eaves on the right side.

Since those holes destroy any isolation you would have got from the roof as an outer-leaf, you are left with no choice but to build a three-leaf ceiling system, with all the negatives that this implies...

Hmmmm. So, ceiling construction would be: Inner leaf (2 x 5/8" drywall on inner ceiling joists) --> air --> 2nd leaf (1 x 5/8" drywall on roof rafters) --> air (with ultratouch insulation and space for ventilation) --> 3rd (outer) leaf (3/4 ply deck + roofing material). Better 3 leaves than a bunch of holes to the outside world, I guess, eh?

4) a good sealing liner for the doors?

Proper acoustic isolation seals are what you need, at least two of them, around the full perimeter of each door, and probably three. Make the last one magnetic, to help keep the door closed, since you cannot use any mechanical latches, as they require drilling holes trough the door, and of course, you can't do that.

5) Sliding door? Yes. John does it all the time with his studios. Pocket door? No. None that I'm aware of.

OK, I knew the pocket door was a long shot anyway… I will try to research for more info on John's sliding doors.

I hope I haven't discouraged you too much! But I'm sure you didn't come here just wanting to hear about what you are doing right... :)

[/quote] Nope, I'm not put off. You've given me some great ideas. At the very least, you confirmed my intuition about where the weak points are for the whole construction. Cheers, Brian

55dB at the property line until 9pm.

That's not too bad, actually. Lucky you!

So a layer of 5/8" plywood, and one layer of 5/8" drywall. I understand the plywood being better for shearing the wall, but would it be a lesser layer than using 2x drywall in the inner-leaf.

For isolation, it's about the same. The density of plywood is a bit lower than that of drywall, but not a huge difference.

Hmm. I could beef up the roof with 5/8" drywall between the rafters.

Yup! :)

I don't have the knowledge you do, but it's hard for me to believe that building out the inner leaf will all be for naught just because I have a skylight.

The fact that it is operable is what degrades the isolation. If it were a proper acoustic-grade skylight, fully sealed in place, it would be OK, but a typical domestic type operable skylight is not going to give you good isolation. Windows and doors are always the weakest links in any studio, even when designed and built properly.

It's a 3-paned window with a watertight seal, so it must have SOME effect on reducing sound.

So it is a 3-leaf window? :) :shock: :!: Isolation of 3-leaf systems is always worse than for the equivalent 2-leaf system of the same mass and total thickness, without exception. It's one of those quirks of acoustics that you don't expect, as it isn't intuitive at all, but there's a different set of physical laws governing one-leaf, two-leaf and three-leaf systems, with different equations being applicable to each. One-leaf wins out in very low frequencies but is lousy over all, two-leaf wins out in mids and highs but can be made to do pretty good in lows as well. Three leaf loses all around.... (except for very high frequencies).

I was planning 2x4s (on edge). It may sound too weak, but with 16 OC rafters, and only 14' x 9', I think it will hold up.

Please don't take this the wrong way, but "thinking" won't keep it all from falling on your head one day! Check the span tables for the type of wood, distances, and loads you will be carrying (both dead and live), and the deflection you need, .... you might be shocked at what you find.... :)

Just to clarify: the conduit comes thru the outer leaf (stucco and ply), straight into a box that is screwed onto the outer leaf framing. So the rigid conduit never touches the inner leaf.

At some point, it has to! You have to get that power to the INNER-leaf, not the outer leaf: you won't even be able to see the outer-leaf at all once the room is finished, so you cannot have the distribution panel on the outer leaf. It HAS to be on the inner-leaf, and therefore you do need to isolate the conduit where it crosses over the gap between the leaves.

I am thinking that nailing the inner leaf to the foundation would create a scenario more like a staggered stud construction instead of a double wall room-in-room.

It's actually more like a single-stud system, since a substantial percentage of each stud is solidly attached to the outer leaf, directly.

As for the flat-framed inner leaf, I'm definitely reconsidering decoupling from the foundation (not nailing too it), in order to frame the 2x4s properly and losing the few more inches of valuable floor space.

If you build the walls "inside-out", then you don't have to lose so much space overall. Search the forum to see how to do that...

Inner leaf (2 x 5/8" drywall on inner ceiling joists) --> air --> 2nd leaf (1 x 5/8" drywall on roof rafters) --> air (with ultratouch insulation and space for ventilation) --> 3rd (outer) leaf (3/4 ply deck + roofing material). Better 3 leaves than a bunch of holes to the outside world, I guess, eh?

In this case, yes. Sometimes 3-leaf is inevitable, and where that happens, it has to be done correctly: most of the mass on the middle leaf, and large air gaps. Don't forget to post your updated plans, and your photos! :) - Stuart -

Greetings forum-dwellers- I thought an update might be in order. I've had my exterior construction completed for almost a year now, and I am finally (!) getting into the fun stuff, the tenuous tasks of sealing, building the inner frame, and getting the doors in. Things I learned, with a nod to Stuart for his excellent responses: 1) I am not going to flat-frame the inner walls, because structural integrity is way more important than those few inches. 2) I am going to build 3 inner walls inside-out, and one wall "regular", due to space constraints with having the sheetrock on the outside. 3) I have built a wall with a normal 30" door in it, where I originally was considering full garage doors at the opening to the street. 4) The GREEN California Building Code allows insulating an attic with spray-foam between the rafters, and does NOT require venting. So that's how I'll avoid poking a bunch of ventilation holes through the exterior leaf to the outside world. 5) I have studied the span tables for the ceiling joists, and I will use 2x4s. AWC says that #1 Douglas Fir 2x4s will handle up to 20psf dead load for a span of 10'3" at 16" O.C. My inner room will be 8'9" and two sheets of 5/8 sheetrock for the ceiling come in around 5psf. I'll see if I can find some photos of construction and put them up.. I have a particular question about my room perhaps needing 3 leaaves... Please check that out here if you have a chance. viewtopic.php?f=2&t=19342&p=132634#p132634 Thanks, Brian