Hi there "cbhris". Welcome!
1. Record rock bands without time restrictions. From what I've been reading that means reducing the level inside the house of ~108db to ~55-60db outside the house?
That sounds about right, yes. Ballpark.
However, there's a few issues that can modify that, both ways:
1) Drums played hard can be louder than that: 115 dBC is typical, and even heading f0r 120 dBC is not out of the question. So if you anticipate having heavy-handed drummers, then you should probably increase your "loud" number a bit.
2) Legal stuff: Your local municipality very probably has "nuisance noise" regulations written into the local bylaws somewhere, so check on-line or go to their offices and get a copy, to find out what your legal requirements are. It's probably something outrageously stupid, impossible to comply with (in most places these days, even walking down the street with your buddy, having a quiet conversation, would already exceed the legal limits), but it's good to know what you should be shooting for, if you hope to keep the cops from knocking on your door.
3) The distance between your building and your property line is a factor in your favor. Sound dissipates over distance, so the larger the distance between your walls and your fence, the better. Usually, the noise regulations specify that your property line is the point where measurements have to be taken to see if you are over the silly limit or not. However, in real life, what your neighbors care about is how loud it is inside THEIR house, so you have the additional advantage of the distance from the property line between you, up to their wall. So when you are figuring out likely sound levels that might annoy them, take that into account: the total distance from your wall to their wall.
4) The empty lots on either side are great news right now! But sooner or later someone will probably buy those and build on them, so your situation will change...
5) Have you also considering incoming noise? For example, when you are trying to record vocals or other quiet things, and a helicopter or plan flies over, or an ambulance with a siren on passes a couple of blocks away (ditto fire engines, cops, etc.). Or your neighbor mows his lawn, or his dog barks incessantly for hours, or.... there's a million "or's" you can add to that list: Rain, hail, thunder, wind.... the list goes on and on. Any of those could be a potential issue that you need to deal with. Eg. You might think that the sound of drums getting out is your biggest issue, but if you have a tin roof and hail is frequent in your area, that could potentially be a bigger problem than drums. Ditto if you live close to a hospital, and ambulances frequently drive right past yoru place with the siren on, or if your studio is located under the departure path from an airport, or close to a railway line... Lots of potential issues that you might want to consider when deciding on your isolation needs.
6) You implied that you though you'd need around 50 dB of isolation, give or take a few points. That is an achievable goal for most DIY home studios. However, if you re-work your numbers and find out that you actually need 70... that's borderline. That's about the limit that can be achieved on a really good budget for a home or project studio, without getting into exotic and REALLY expensive solutions. 60 dB is probably about as far as most home builders can expect, and even that requires very careful design and very careful attention to detail in the actual build.
I mention all of the above to highlight the importance of assessing your real isolation needs as accurately as you can. There's a big difference in complexity and cost between shooting for 50 dB, and shooting for 70 dB. That likely implies a budget increase of 400%, believe it or not....
2. Be able to hear in my monitors what the mics are hearing.
This is certainly related to your overall isolation number, but isn't the same. Sorry to be cryptic! The overall isolation to the outside world is one thing, but the isolation between rooms inside the studio is another thing. The two are related, since the isolation design is a system, not individual parts, but you need to take both into account when designing your walls, windows, doors, etc. It is possible to have different levels of isolation between rooms as compared against isolation to the outside world,but usually it is easier to just design for the same level all around. It keeps things simple.
3. A structural engineer will be coming out to the house to look at some other things, and I'd like to be able to ask pertinent questions while they're there.
Excellent! Smart move! From what you say, I expect that your number one question would be "How do I remove the existing floor and replace it with a concrete slab?". More on that later...
1. It's an old house with wood decking on all of the floors
... and now we get to "later"!
This is your biggest problem, by far. You need reasonably high levels of isolation, it seems, and the number one key point in stopping sound, is mass. Heavy, solid, rigid, thick, dense, massive, building materials. Main issue here, being "heavy". Way beyond the ability of typical wood deck flooring to support. The best solution is simply to replace that wood deck flooring, with a concrete slab. Concrete has the mass, density, and structural integrity to provide the base for your entire studio build. So your question to the structural engineer, should be how you can do that: How you can rip out the existing flooring without causing the entire house to collapse, and how you can pour your new slab without damaging the remaining shell.
1. The house will be dedicated to sound if my goals are feasible, so I can do whatever I like as long as it's safe. No one has to be comfortable when I'm making music except the neighbors.
I think you'll find it much easier to make good music if your musicians and sound engineers are comfortable while doing so!
Ergonomics and aesthetics are a big part of studio design, very close behind isolation and acoustics. When I'm designing a studio for a customer, I try to put myself in the position of a musician or engineer involved in a session, and think through things like: "How can I make it easier to load the gear and instruments in and out, before and after the session? How can I improve visibility between the rooms, so everyone can see each other while they are tracking? How can I make it look nicer, brighter, more "airy", cleaner, warmer, more attractive, without compromising acoustics? How can I make it easier to go back and forth between the CR and LR, to set up mics and instruments?" Etc. It's just as important to have happy, content, comfortable musicians and engineers, as it is to have outstanding acoustics. A place that sounds wonderful but is dark, dingy, smelly, cold, and unpleasant, and requires you to go through six sets of double doors between the LR and CR on each trip to adjust a mic, while the engineer can't see the musicians, or the vocalist can't see the lead guitarist or drummer, the entry door to the building for bringing ibn instruments and equipment is way down the far end of a long, narrow, twisting passage and down a flight of stairs... well, that's not a good design in my book.
2. It is a rehab, so all of the walls are wide open.
Excellent!
4. I tend to get obsessed with things.
Even more excellent! This means that you'll really, really want to do everything you can to make it as good as it can be, and it also means that you'll spend way, way more than you even imagined initially...
There is a non-functioning fireplace that can be removed if necessary.
Might not be necessary. Is that stone? Brick? Concrete? Something else? It might be possible to just block the chimney, and use the fireplace as a visual accent, or even for acoustic purposes.
Ceilings are 9'
Great! The higher, the better.
I will try to make a 3D model in sketchup as soon as I can learn it.
Do not try to use the totally silly, "SketchUp Free" version, which is a piece of browser-based stupidity. Total garbage, useless. Don't wast your time. Rather, download and install "SketchUp Make 2017". That's the actual SketchUp program that you install on your computer. Don't confuse that with "SketchUp Free". They are both free! But the one called "free" is worthless trash. The one called "Make 2017", is good, and that's what you want.
Budget: I'm trying to get a budget in mind, but I don't know what will be necessary yet. If I can stretch the renovation over time, the budget will increase.
Think of a very large number. Multiply it by another large number. Add in a few other large numbers. Divide by a small fraction. That should get you close to how much you will actually spend on this...
More seriously: call a few local contractors, and ask for their "flat rate per square foot" for converting an unfinished garage into a living room or additional bedroom. If you can get a few quotes like that, drop the cheapest and most expensive one, average the others, add 30%, and you have rough idea of how much this is going to cost you, realistically.
Also, the place is pretty much completely stripped. Along with wide-open walls, there is not much plumbing or electrical either.
That's REALLY good.
So basically you have a blank slate, and you can use all of the internal area of the ground floor and basement for your studio, while leaving the other floors for offices, green room, storage, kitchen, bathrooms, etc.
One question: Is this going to be a commercial facility, or a hobby facility? If commercial, then very likely you will be subject to ADA requirements, so it will have to be wheelchair accessible, including at least one bathroom. Major point! However, if this is just your own personal, private, hobby studio, for you to fool around in with friends and family, then that is probably not applicable. Your architect can fill you in on the details for both situations, so make sure you look into this, and determine of ADA rules are applicable to you.
I would suggest that you start your design be deciding how many actual acoustically isolated rooms you need in the studio itself (eg. LR, CR, vocal booth, iso-booth dedicated drum booth, machine room, etc.) and do a rough layout of where you think those would fit on the ground floor and/or in the basement, allowing for at least 6" inner-leaf walls for each room, then post your rough layout here. Then other members here can offer on advice on improving that, so you can move forward from there, with the design process.
- Stuart -