Detached Garage Studio Conversion

[SEEK18]

Hi. After 12 years of marriage, 2 records, 3 kids and 5 cities my wife has given me permission to build a recording studio! We just bought a new house with a detached garage in the backyard and it was already converted to a livable space by the previous owners like 30 years ago. So some friends and I gutted the wall-to-wall bookshelves and the damaged linoleum floors and I'm hoping to begin framing in the next couple of weeks. However, there are quite a few challenges to the space which is why I'm here. First the specs, then the questions.

1. Dimensions:
A. 17'x19'x11' (8' walls that run up to an 11' plateau ceiling)
B. 3.5" drop floor from the doorway thresholds
C. 2 sets of glass paned french doors, no windows or other openings/vents

2. Purpose:
A. mixing and recording space for singer/songwriters and solo instrumentalists (drums included)
B. live performances in front of french doors onto patio

3. Challenges:
A. french doors open inward
B. tight budget for soundproof phase (under $2,000)
C. kids playing in the yard while I'm tracking
D. neighbors driveway on other side of my fence is about 15' away and they regularly play loud bass through subs in their car trunks.
E. I've never framed a room or a wall or anything before, but I'm good with a drill and a saw

4. Plans:
A. Build a room within a room that has its own solid door. Creating a small lobby next to the french door entrances that can double as a stage to the patio for house concerts.
B. Make the room a mixing and live track dual purpose room that withstand the severe bass frequencies from my neighbors.



5. Questions:
A. Am I correct in thinking 2x4 framing is as good as 2x6 or 2x8 for sound proofing the room within a room as long as the inner wall is far enough away from the outer wall?
B. Do I need to decouple the drywall from the studs on the inner wall?
C. Do I need a floating floor if it's on concrete slab?
D. How far should the inner wall be from the outer wall if there's significant low end frequencies being played from a subwoofer 15' from my outer wall? And, can I leave a larger air gap on one side and a small on the other side where my quieter/further away neighbors live?
E. Do I need a new ceiling framed for the live room?
F. Is green glue necessary or will double leaf on both sides of studs and rockwool insulation do the trick?
G. What are the ideal dimensions for this live room?
H. Will a mini split do the trick for heating/cooling? What about humidity levels?

This is quite new to me so thank you in advance for any advice you guys can lend!

Happy New Year!

[gullfo]

so, there are a few approaches.

one is to start by beefing up the existing walls and roof in the garage - you can add mass in-between the studs and joists - adding 2x 5/8" drywall (or an equiv mass - 1" MDF for example) onto the exterior sheathing will definitely help with the isolation

- HOWEVER -

before doing so you MUST get a structural engineer to assess your structure and determine what kind of load you can add - particularly the roof, even as a dead load, you'll need to take into account your local ordinances for wind, seismic, snow, etc. you'll also want that assessment if you're going to build a room within a room because the floor of the garage may not support the weight of the new interior structure, and it's likely you'll want some sway bracing to the existing structure even if it's not specifically required.

insurance companies are likely not to pay out in the event an improperly built structure crushes it's occupants...

exterior walls and roof need moisture barriers. the roof will need ventilation.
heavier windows and doors can be installed.
seal up all gaps and cracks.
you will learn to deeply hate caulk, however, caulk is your loving friend.

OXYGEN - not surprising, 10 out of 10 people who have suffocated or experienced near-death from asphyxiation, due to having no fresh air exchange in a newly constructed hyper-insulated / sealed box, agree that having a proper air exchange system (preferably with heating/cooling) is another MUST. plan for a proper air system - a split AC unit WILL NOT provide fresh air, so i recommend a forced air system to handle heating/cooling and an ERV for air exchange.
this will likely be the single most expensive part of the build

so even before you build a room within a room, you may find these several steps will already do a pretty significant job for you. and sometimes it may even be enough.

once you're good-to-go on the inner room - you'll be using 2x6 walls because your ceiling spans (and again mainly dead weight) will be in the order of thousands of pounds (read: several tons is possible) so 2x4 walls would mean going with 16" o.c. vs 24" o.c. and it's ideal to get the wider stud spacing if you can.
depending on how you may divide up the space (if at all), will determine if you could use 2x4 24" o.c..

on the frame spacing - if you beef up the exterior walls and seal them, generally speaking, leave a 1" gap around the edge to the inner wall frame. if it's a 2x6 frame, then you have a gap of (if garage is already 2x6) roughly 11-12" air gap which should do a decent job. (2x 5.5" + 1" gap - beef-up mass thickness).

the floor of the garage is already earth damped so floating the floor is not likely needed - although the neighbor with the subs playing a lot of loud LF material could still penetrate the walls and roof but if done correctly you could likely filter that out from any mics that pick it up.

the air gap will be filled with insulation - consider 2x R30 insulation which will be slightly compressed against the mass layers.

[SEEK18]

Ok. Thanks so much, Glen! I'll look into a structural engineer pronto before posting again.