Another Garage Build, By an Airport...

[wadesey]

Hi, I’m a few months into research and planning of a simple, single room studio in a detached garage. I've been reading through the countless other builds like this and learned a ton, but am left with a few specific isolation questions that I can't figure out.
I've attached a super rough image of the basic framing/dimensions of the entire garage. Here's a link to the sketchup file.

Background:
The studio will be primarily a film+TV composing and songwriting room. I’d like to be able to record acoustic guitar, electric guitar (low wattage amps), percussion, singing and voiceovers with adequate isolation — I’ll try to express “adequate” below. There won’t be frequent full-on drumming or cranked Marshalls happening, so I’m more concerned with sound coming in than going out.

Dimensions:
16’10” x 19’9” x Variable height
The ceiling follows the pitch of the “flat” roof and varies from 7’11” at the shortest, to 9’ at the highest. I made some notes on the sketch, since I don’t know how to draw that...

Existing construction and materials that I know:

Ceiling/Roof:
- Flat roof that slopes down to drain at the southeast corner (the wall opposite the entry door and window)
- Original ceiling of garage is redwood tongue and groove and is 4" higher than the current drywall ceiling
- 4x8 ceiling beam that was replaced in 1985, covered in drywall
- ceiling joists are 2x4 30-32"oc -- but they are full size redwood 2x4s...
- 1/2" drywall screwed to joists
- insulation between drywall and redwood

Walls:
- outer wall is stucco and paper- not sure how thick the stucco is
- existing wall framing is 2x4 16”oc
- encapsulated Johns Manfield R13 insulation in walls
- aluminum door is sealed and has 2x4 wall in front of it
- concrete slab floor that was re-poured at some point in the 70s or 80s

Things in room I can’t change:
- clothes washer and dryer location by entry door (may be able to change to stacked instead of side by side though)
- support beam location

Main problem: I’m about a mile from a pretty busy regional airport. Jet engines on departure point toward the wall with entry door and window. Small planes frequently fly directly overhead at altitudes of 300-1000 feet...

SPL levels inside with current construction (C weighted, measured with Faber Acoustical Soundmeter iPhone app):
35-40 dB - no air traffic
48-56 dB - jet take off
50-60 dB - small plane take off

SPL levels outside garage:
50-55 dB - no air traffic
65-70 dB - jet take off
70-80+ dB - small plane take off

Isolation Goal:
I’m not sure the best way to express the level of isolation I’d like, but I would think improving the ~15-25dB reduction provided by the current construction to ~40dB or more reduction… I believe this is frequency dependent and would understand if this isolation level isn’t possible in very low frequencies.

Current isolation plan:
- One plan is to purely beef and seal... Trying to gain a modest amount of isolation through mass and sealing. Remove existing drywall, seal everything, re-place 1/2" drywall on outer sheath plus layer of 5/8", re-place insulation, add 1-2 layers of 5/8" drywall on inside of stud. Replace and seal entry door, etc.

- Other plan is design new inner room

Questions:

1) Is it possible to build a ceiling that runs just under where the current ceiling is at roughly 8'), then dips below the beam (around 7'6"), and back up? I've seen soffits around objects running parallel to the joists, but is something like that possible perpendicular? Ideally the inner room joists would run between the outer ones to maximize headroom. Maybe I'm searching the wrong thing here and throughout the Internet, or maybe it's impossible, but I can't figure it out.

2) Would a beef and seal only project potentially provide 40dB of isolation?

My budget for the project is ~$12,000 (includes all construction, electrical, hvac, acoustic treatment). I know, low...

Thanks a million for any insight!

[Soundman2020]

1) Is it possible to build a ceiling that runs just under where the current ceiling is at roughly 8'), then dips below the beam (around 7'6"), and back up? I've seen soffits around objects running parallel to the joists, but is something like that possible perpendicular?

Yes, it is possible. Not a problem.

That said, a better option would be to get the beam raised, and/or replaced with something that is stronger but lower profile. That 12" dip in the middle of the room is going to be a major pain, both visually and also acoustically...

2) Would a beef and seal only project potentially provide 40dB of isolation?

You mean just a single leaf? You could do that, but you'd need a huge amount of mass. There's an equation in Physics, called the empirical Mass Law equation, that tells you exactly how much mass you will need. It goes like this:

TL = 14.5 x Log(M) + 23

Where "M" is the surface density (in PSF), and TL is the Transmission Loss you are looking for (in dB).

Do the math, and you'll find that you need a surface density of 15 pounds per square foot to get 40 dB of isolation. 5/8 drywall has a density of a bit more than 2 PSF, so you'd need to beef up with about seven layers of drywall.... (!)

And I'm pretty sure that would way exceed the structural load-bearing capacity of your joists!

Probably not a good option...


- Stuart -

[wadesey]

Thanks for the input! The project has stalled out due to some pretty serious structural problems that were revealed after the drywall was removed (termites, rot, mold, etc...), so still in the planning stages months later.

1) Is it possible to build a ceiling that runs just under where the current ceiling is at roughly 8'), then dips below the beam (around 7'6"), and back up? I've seen soffits around objects running parallel to the joists, but is something like that possible perpendicular?

Yes, it is possible. Not a problem.

That said, a better option would be to get the beam raised, and/or replaced with something that is stronger but lower profile. That 12" dip in the middle of the room is going to be a major pain, both visually and also acoustically...

I would love to replace the beam, but I don't think the budget will allow for that. There's only 3.5" of clearance between the top of the beam and the roof deck, so raising isn't an option either, unfortunately.

I'm still trying to understand how it's possible to have an independently framed ceiling dip below the beam and back up. I've tried searching here and elsewhere and can't find any good examples. All I could think of was using smaller beams on either side of the large beam, the smaller ones connected only to the inner leaf walls+joists. Unless the only way is to have the inner leaf connected to the outer leaf at the beam? Mitigated by using RSIC clips or something? I'm definitely failing the IQ test on this one...

[Soundman2020]

some pretty serious structural problems that were revealed after the drywall was removed (termites, rot, mold, etc...),

Ouch! That's not a pleasant thing to find! It must have been very disappointing.

On the other hand, you did find it before the whole thing collapsed on your head, so I guess from that point of view, it's a good thing.

Still, setbacks like that are not fun.

so still in the planning stages months later.

Now THAT'S a good thing! Planning is very, very important. Building a studio is about 90% design, and only 10% actual construction. When I first heard that many, many years ago, I thought "Yeah, right... that's just to scare people", but it turns out to be very true. The more time you spend designing, the less time you'll need for actually building, and the cheaper it will be. Yup: cheaper. designing properly saves you money, and it can be a large amount...

I would love to replace the beam, but I don't think the budget will allow for that. There's only 3.5" of clearance between the top of the beam and the roof deck, so raising isn't an option either, unfortunately.

Photo's of the actual beam, room, and roof would help to understand the situation better...

I'm still trying to understand how it's possible to have an independently framed ceiling dip below the beam and back up. I've tried searching here and elsewhere and can't find any good examples. All I could think of was using smaller beams on either side of the large beam, the smaller ones connected only to the inner leaf walls+joists. Unless the only way is to have the inner leaf connected to the outer leaf at the beam? Mitigated by using RSIC clips or something? I'm definitely failing the IQ test on this one..

Post the actual SketchUp SKP file that you showed above, or if it is too big then post it to a file sharing service such as DropBox and post the link here. That way I can download it and show you how it's done.


- Stuart -

[wadesey]

Thanks a million!

After reading thoroughly I definitely caught on to the make-sure-you're-design-is-complete-before-you-start theme...

Here's a photo of the beam (drywall is still on it, obviously). The stud wall to the right is the one that was constructed by a previous owner about 12 years ago in front of the garage door, really only to hang drywall from. The beam breaks up the 20' span of the 2x4 rafter/joists that are spaced 32"oc and connects to the header above the garage door. The joists are on top of the beam and the tongue and groove roof deck is attached directly on top of the joists.
The wall to the left (back) was constructed at the same time as the beam (1985), after from what I've read from old building permits, the old beam broke. The joists do hang from this wall.

beam1.JPG

And here's a photo of the wall opposite the garage door. The roof is flat and both this and the garage door side have a parapet to give the illusion of a pitched roof. This is looking up the wall into the parapet.

parapet.JPG

The Sketch Up file is unfinished, but has the outer structure and the stuff that can't be moved accurately represented. Also has a rough outline of the inner leaf walls/dimenstions. Hopefully enough to quickly show me how to get around that beam?
https://www.dropbox.com/s/ll37kt5szccqf ... 1.skp?dl=0

[wadesey]

Apologies if this bump is out of line, but any chance of quickly looking at the sketchup linked above to see if framing around that beam is possible, Stuart? Many thanks!

[Soundman2020]

Here's a photo of the beam (drywall is still on it, obviously).

Maybe it's just the way the photo was taken, but to me it looks like that beam is bowing down, bending.... not a good sign! Hopefully I'm wrong about that.

I also noticed that you have a flat roof, which means that the only way you could raise that beam is to raise the entire roof! Probably not an option...

So, the solution to building your ceiling is to run the joists in the same direction as that beam runs, parallel to it, then build a soffit that ducks under the beam. You'd have to do the same for your two end walls: There would be a section in the middle of each of those where the top plates would be lower than the rest. It will be a pain to do that, but I don't think you have any other options.

The dimensions of the joists will have to be calculated. Your best bet for doing that is a structural engineer. You could use span tables to figure it out, but that might not pass inspection: they will likely ask for the engineer's report.

- Stuart -

[wadesey]

Thanks for the info!
Even though that was what I feared was the only answer...

Unfortunately, the distance the inner ceiling joists would need to span if run that way would be longer than 2x4 is rated. Adding a beam to break up the span wouldn't work because the other beam is in the way. And 2x6 joists would bring the ceiling height down to where I wouldn't want to be in there all day...

So, it looks like independent ceiling is out. I'm looking into adding joists to the current ceiling/roof to make them 16" oc -- as opposed to the current 32" -- then hanging two layers of 5/8" drywall. Before I get too far, I'll check with a structural engineer to see if this is even feasible...

I think I've given up on having a super isolated room -- 80% of what I do doesn't really need one, and building a more isolated vocal/acoustic guitar/amp booth might be fine.

RE: the beam sagging. Due to the pitch of the roof, it isn't straight across -- it's about 3-4" higher on one side -- so I'm hoping that's why it looks like that. I'll probably take the drywall off of it to get a better look...

[Soundman2020]

Unfortunately, the distance the inner ceiling joists would need to span if run that way would be longer than 2x4 is rated.

Right. I wasn't suggesting 2x4's for your joists. Studio ceilings rarely use 2x4's, as they just can't handle long spans with large loads. Normally I use at least 2x6, sometimes 2x8, and occasionally even more.

Is there a reason why you can't use 2x6's? Are they hard to find where you live? Too expensive? Some other reason?

And 2x6 joists would bring the ceiling height down to where I wouldn't want to be in there all day...

Not true. The acoustic height would be exactly the same, no matter what size joists you use, and the bottom cord of the joists would still be higher than the "drop-down" soffited section around the beam. That would remain at the same low height, no matter what you do.

So, it looks like independent ceiling is out.

I still don't see why! Nothing changes just because you have to use larger joists. The acoustic height is the same (height of the drywall), and I don't see why having the joists 2" lower, but still way higher than the bottom of the beam, would be a problem.

- Stuart -

[wadesey]

Not true. The acoustic height would be exactly the same, no matter what size joists you use, and the bottom cord of the joists would still be higher than the "drop-down" soffited section around the beam. That would remain at the same low height, no matter what you do.

I had decided to do a standard ceiling vs inside out, which is what you're referring to, correct?
But I just went back and tried to draw it inside out and it seems like it could work! One wall would actually have to be so low on one end that the top plate would already be below the beam with enough clearance, which seems like it would make the soffit simpler?

The only hang up is in trying to make the ceiling modular so that it can be lifted in to place. Since the outer leaf beam is in between the opposite inner leaf wall top plates, I can't figure out how to get a cross beam in to break up the joist span.

Are there other ways to break up the modules?

Or will it be necessary to hoist up ~15 ft long joists with two layers of drywall attached?...

Also, does having a sloped ceiling make the inside-out modular ceiling building considerably more difficult?

And finally, even though the acoustic height of the ceiling will be higher inside-out, won't the perceived height still be considerably lower after the cavity is filled with insulation and fabric applied to the bottom?

Thanks again -- it finally feels like I'm making progress!

EDIT: including updated sketchup file. Inner room dimensions are not final (probably too square) but that shouldn't affect ceiling much or at all: https://www.dropbox.com/s/bh4w5g1c4zk0p ... 0.skp?dl=0