Inconsistent Mass Distribution In-Wall

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thecr4ne
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Inconsistent Mass Distribution In-Wall

Post by thecr4ne »

I'm beginning to convert an 8'x12.5' room in my garage into a control room. It's built into the corner of the garage and has 2 exterior walls, one stucco ext, one wood ext. in which I'd like to increase isolation as I live on a busy street and get lots of road noise. I understand adding mass is the way to go, and the most massive material I have on hand is scrap granite (from counter-top material)

My thought was to put it between the studs against the exterior sheathing before adding rock wool insulation, but I don't have enough granite to evenly fill the whole wall. Would it still make a difference even if it's only in the lower half of the wall? or should it be spaced out to every other stud bay? would it be problematic if it doesn't fill the entire area of the stud bay?

Thanks.
Paulus87
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Re: Inconsistent Mass Distribution In-Wall

Post by Paulus87 »

thecr4ne wrote:I'm beginning to convert an 8'x12.5' room in my garage into a control room. It's built into the corner of the garage and has 2 exterior walls, one stucco ext, one wood ext. in which I'd like to increase isolation as I live on a busy street and get lots of road noise. I understand adding mass is the way to go, and the most massive material I have on hand is scrap granite (from counter-top material)

My thought was to put it between the studs against the exterior sheathing before adding rock wool insulation, but I don't have enough granite to evenly fill the whole wall. Would it still make a difference even if it's only in the lower half of the wall? or should it be spaced out to every other stud bay? would it be problematic if it doesn't fill the entire area of the stud bay?

Thanks.
It's an interesting question, but unfortunately wherever the granite is not would become a weak link in the overall isolation, and isolation is only as good as its weakest link. It's a shame you don't have more granite!

You could use multiple layers of drywall in the stud bays, drywall is very cheap and very dense, if you used 2 or 3 layers on all the walls and the ceiling and it was sealed air tight you'd have a good improvement, but a single leaf assembly can only get you so far. Even a concrete block assembly has limits by itself, but when used in conjunction with a decoupled second leaf with an insulated air gap in between it can become an excellent isolation assembly.
Paul
thecr4ne
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Re: Inconsistent Mass Distribution In-Wall

Post by thecr4ne »

Paulus87 wrote:...isolation is only as good as its weakest link. It's a shame you don't have more granite!...
.
Thanks Paul,
I had a feeling that was the case. I'll forgo the granite in favor of drywall then. Since there's currently drywall on the walls, that will get carefully cut and set back into the stud-bays, and possibly a second layer if I have enough scraps around, then the rock wool, then drywall. I don't know that I'll be able to sufficiently decouple the drywall from the framing, but if I can find a reasonable way to do so within my means, I'll go for it, but probably can't manage doing so for all the walls. Trying to balance budget, effective isolation/treatment and time.
Paulus87
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Re: Inconsistent Mass Distribution In-Wall

Post by Paulus87 »

thecr4ne wrote:
Paulus87 wrote:...isolation is only as good as its weakest link. It's a shame you don't have more granite!...
.
Thanks Paul,
I had a feeling that was the case. I'll forgo the granite in favor of drywall then. Since there's currently drywall on the walls, that will get carefully cut and set back into the stud-bays, and possibly a second layer if I have enough scraps around, then the rock wool, then drywall. I don't know that I'll be able to sufficiently decouple the drywall from the framing, but if I can find a reasonable way to do so within my means, I'll go for it, but probably can't manage doing so for all the walls. Trying to balance budget, effective isolation/treatment and time.
If you tell me the exact configuration you'll likely go for then I could probably run it through INSUL to predict what kind of transmission loss you can expect, and at which frequencies.
Paul
thecr4ne
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Re: Inconsistent Mass Distribution In-Wall

Post by thecr4ne »

Paulus87 wrote: If you tell me the exact configuration you'll likely go for then I could probably run it through INSUL to predict what kind of transmission loss you can expect, and at which frequencies.
I'm still trying to assess my options, but I'll go over what I'm currently thinking. My primary goal is to limit road noise. Cars/trucks/busses driving by and car doors slamming shut are the big offenders.

Front wall: 8ft x 8ft, wood 1"x12" exterior siding, studs at 16" centers and fireblocks every 24"
My plan is to insert 2 layers o 1/2" drywall (no green glue) in each of the stud bays, then insert 3" rock wool to fill the remaining void.
After that options are:
A. Just close up the wall without decoupling, 2 layers 1/2" drywall.
B. build floating "Inside out" wall with 2 layers of 1/2" drywall. my thought here is to do the framing flat, attaching the drywall to the long side of the 2x4s instead of the short side as is typical, and mounting the wall in rubber U-shaed joist isolators on all sides.
C. Build out soffits for Large monitors, which would be filled with fiberglass insulation, and skinned with either drywall or left "open" and covered with fabric.
D. Some combination of A or B, and C.

Side wall: 8ft x 12.5ft, 1" thick stucco ext, studs at 16" centers, fireblocks at 48", one 42"x42" window.
Same 2 layers of 1/2" drywall inserted against stucco (no green glue) then 3" rock wool to fill the rest.

Same options as front wall except for the soffits.

Floor is vinyl tile on a concrete slab and will likely stay as-is, ceiling is drywalled already, and might get insulated above, and maybe the joists covered on top with something but I don't think I can manage to do much to it re: decoupling. I could maybe add another layer of drywall but am not planning to currently.

I'm definitely open to simpler suggestions if you have any. I'm new to this and the expensive complicated solutions seem to be more prevalent than simple affordable ones.
DanDan
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Re: Inconsistent Mass Distribution In-Wall

Post by DanDan »

Just a technical correction. Fibre is used in the Air Gap of MAM systems. A full fill of light fibre will damp air resonances in the gap. Touching the slabs dampens them.
These combine to deliver a nice 10dB or so of Transmission loss.
thecr4ne
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Re: Inconsistent Mass Distribution In-Wall

Post by thecr4ne »

DanDan wrote:Just a technical correction. Fibre is used in the Air Gap of MAM systems. A full fill of light fibre will damp air resonances in the gap. Touching the slabs dampens them.
These combine to deliver a nice 10dB or so of Transmission loss.
So loose fiberglass instead of rock-wool if I were to just close up the walls?
DanDan
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Re: Inconsistent Mass Distribution In-Wall

Post by DanDan »

Full fill Light.png
Any type of fibre. Partition or Attic Rolls or Blankets.
A full fill but not compressed.
Void Density.png
thecr4ne
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Re: Inconsistent Mass Distribution In-Wall

Post by thecr4ne »

The rock wool is designed to leave an 8.5mm gap between it and the gypsum board, Is this logic treating the rook wool as mass and that gap as the air gap? If the logic is entirely flawed I'll be better off exchanging the rock wool for fiberglass and recouping the price difference.
DanDan wrote:
Full fill Light.png
Any type of fibre. Partition or Attic Rolls or Blankets.
A full fill but not compressed.
Void Density.png
Paulus87
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Location: Wales, UK

Re: Inconsistent Mass Distribution In-Wall

Post by Paulus87 »

thecr4ne wrote:The rock wool is designed to leave an 8.5mm gap between it and the gypsum board, Is this logic treating the rook wool as mass and that gap as the air gap? If the logic is entirely flawed I'll be better off exchanging the rock wool for fiberglass and recouping the price difference.
DanDan wrote:
Full fill Light.png
Any type of fibre. Partition or Attic Rolls or Blankets.
A full fill but not compressed.
Void Density.png
the mass of the rock wool is so tiny in comparison to the drywall that it's insignificant. If you do not need it for the added thermal benefits, then return it and get a nice bit of money back in exchange for the lower density (10-20kg/m3 for example).

If you would like the added thermal benefits of the rock wool then you could put the rock wool in the bays and fill the rest of the gap with the lightweight fluffy stuff.
Paul
thecr4ne
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Joined: Sun Sep 26, 2021 9:00 am

Re: Inconsistent Mass Distribution In-Wall

Post by thecr4ne »

Paulus87 wrote: the mass of the rock wool is so tiny in comparison to the drywall that it's insignificant. If you do not need it for the added thermal benefits, then return it and get a nice bit of money back in exchange for the lower density (10-20kg/m3 for example).

If you would like the added thermal benefits of the rock wool then you could put the rock wool in the bays and fill the rest of the gap with the lightweight fluffy stuff.
Returned the rock wool yesterday and found a local guy selling R21 fiberglass unfaced at a price so low I got enough for all the walls and still saved $8 over the cost of the rock wool.

Some other updates. I got a deal on genie clips, so I'll be doing the clips/hat-track decoupling on the walls and ceiling. I also found a reasonable price on OSI SC-175 (which I understand to be functionally comparable to green glue) so I'm awaiting delivery on that.

Started tearing things apart yesterday. The exterior wall with Stucco on the outside is not flat inside (the back side of stucco), and the stucco is likely sufficiently massive as is, so I'll just add clips and hat-track before adding the drywall. The wall with wood siding, I used a roto-zip router to cut the existing drywall along the studs/fireblocks, which I'll then set back against the wood siding and caulk in place before insulating. Both the Stucco and the Wood siding are backed with tar paper, not sure if that will effect anything.

So front wall, 8ftx8ft will be: 3/4" wood, felt paper, 1/2" drywall, 5 1/2" fiberglass insulation, 5/8" drywall on isolating clips/hat track
Side wall 8ftx12ft will be: 1" stucco, felt paper, 5 1/2" fiberglass insulation, 5/8" drywall on isolating clips/hat track. This wall has a 42"x42" double pane picture window (doesn't open) which will be re-set with the SC-175 sealant, and possibly treated later on.

The other two walls and ceiling will also be decoupled with the clips/track and get new drywall, I'm trying to figure out how to set the clips back a bit to minimize the overall room volume loss. I am also considering building a rack into the 12ft wall opposite the exterior stucco wall. Still working that out, and it may happen after the drywall is installed.
Paulus87
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Re: Inconsistent Mass Distribution In-Wall

Post by Paulus87 »

thecr4ne wrote:
Paulus87 wrote: the mass of the rock wool is so tiny in comparison to the drywall that it's insignificant. If you do not need it for the added thermal benefits, then return it and get a nice bit of money back in exchange for the lower density (10-20kg/m3 for example).

If you would like the added thermal benefits of the rock wool then you could put the rock wool in the bays and fill the rest of the gap with the lightweight fluffy stuff.
Returned the rock wool yesterday and found a local guy selling R21 fiberglass unfaced at a price so low I got enough for all the walls and still saved $8 over the cost of the rock wool.

Some other updates. I got a deal on genie clips, so I'll be doing the clips/hat-track decoupling on the walls and ceiling. I also found a reasonable price on OSI SC-175 (which I understand to be functionally comparable to green glue) so I'm awaiting delivery on that.

Started tearing things apart yesterday. The exterior wall with Stucco on the outside is not flat inside (the back side of stucco), and the stucco is likely sufficiently massive as is, so I'll just add clips and hat-track before adding the drywall. The wall with wood siding, I used a roto-zip router to cut the existing drywall along the studs/fireblocks, which I'll then set back against the wood siding and caulk in place before insulating. Both the Stucco and the Wood siding are backed with tar paper, not sure if that will effect anything.

So front wall, 8ftx8ft will be: 3/4" wood, felt paper, 1/2" drywall, 5 1/2" fiberglass insulation, 5/8" drywall on isolating clips/hat track
Side wall 8ftx12ft will be: 1" stucco, felt paper, 5 1/2" fiberglass insulation, 5/8" drywall on isolating clips/hat track. This wall has a 42"x42" double pane picture window (doesn't open) which will be re-set with the SC-175 sealant, and possibly treated later on.

The other two walls and ceiling will also be decoupled with the clips/track and get new drywall, I'm trying to figure out how to set the clips back a bit to minimize the overall room volume loss. I am also considering building a rack into the 12ft wall opposite the exterior stucco wall. Still working that out, and it may happen after the drywall is installed.
OSI SC-175 is not a green glue equivalent or substitute... unless you're talking about the green glue sealant? the green glue designed to go between drywall layers is something different, the green glue sealant is just a non hardening caulk like OSI SC-175. Don't put OSI SC-175 between your drywall layers, just use it to seal gaps and seams.

Can you talk more about your plans for the ceiling? What is the current structure? Do you have a vented roof?
Paul
thecr4ne
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Re: Inconsistent Mass Distribution In-Wall

Post by thecr4ne »

Paulus87 wrote:
OSI SC-175 is not a green glue equivalent or substitute... unless you're talking about the green glue sealant? the green glue designed to go between drywall layers is something different, the green glue sealant is just a non hardening caulk like OSI SC-175. Don't put OSI SC-175 between your drywall layers, just use it to seal gaps and seams.

Can you talk more about your plans for the ceiling? What is the current structure? Do you have a vented roof?
Can you say more about the specifics of green glue and if there is a more affordable alternative? I'll stick to seams with the sc-175.

Ceiling is 2x4 joists, 16" centers, running the length of the room (12.5ft). There's currently plywood on top of them, which will be removed. It's in a garage with gable vents, and the rest of the garage has no ceiling. Current plan is to just get new drywall up with clips/channels, which I hope to recess a bit so the drywall is ultimately closer to the current ceiling height. Will probably just block between joists and mount the clips to the blocks. Budget/time constraints will probably delay anything beyond that for a while, but I'll definitely insulate it at the very least, and if it helps to enclose the insulation that's doable.

Air conditioning is the big question-mark. I'm in Southern California and it's 90+ degrees F here May-Oct, so it will be necessary. Not there yet though.
thecr4ne
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Re: Inconsistent Mass Distribution In-Wall

Post by thecr4ne »

This wall is complete. No granite, ha, but each of the ~24x16" cells in the wall got a piece of the old drywall and 3/8" plywood added against the outer sheathing, edges caulked with SC-175 and tacked in place with a few nails around the edges. Genie clips were installed on 1 1/8" furring blocks to achieve sufficient depth for 5.5" R21 fiberglass insulation, which was installed, gaps filled, and cut to avoid compression by hat-track. 1 layer 3/16" hardboard (no holes) was installed on the hat track, then a layer of 5/8" type X drywall.

This wall is probably overkill, but there's a lot of road noise on the other side of it. Still have 3 other walls, a window and a ceiling to complete, so time will tell if the result is enough to block most of that. So far putting my ear on the wall is nice and quiet and a tap on the wall yields a nice low thud. Encouraging.

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