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PostPosted: Tue Oct 17, 2017 1:15 am 
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Joined: Thu Oct 05, 2017 10:33 am
Posts: 6
Location: Houston, TX, USA
Hey guys!

My name is Jeff, and I'm new to the site. I've been planning a new studio build in my backyard in the Houston Texas area for some time now. I plan on posting my entire plans soon, but I've run into a snag with the design and thought I would go ahead and ask for some assistance.

A little background: I'm a drummer and the recording engineer for our band. The space will mainly be used by me for practice and recording using an acoustic drum setup with volumes usually in the 105 db range. The plan is for a 14'w x 19'd x 10'h combination control and tracking room. I will occasionally have the whole band over to record, but I plan on just doing direct inputs with the guitars and have the vocals soft and then redub, so the overall volume shouldn't increase much. Our neighborhood is pretty spaced out with the next closest house being approximately 100 ft away. Street is fairly quiet. So goal would be to have around 50-60 db of isolation (not really sure if this is the right way I should express how much isolation I want, but it makes sense to me). I plan on constructing a room within a room with 2x4 spaced 16" oc with dbl 5/8" drywall, green glue, R13 insulation on the inside and 2 layers of staggered sheathing with insulation on the outside. Exterior dimensions are 16' x 21' x 11', which wil give me a few inches of air space on each side, including the ceiling. Roof will either be monoslope or just traditional gable. Planning currently to have OSB on rafters below a metal roof. Slab will be simple concrete.

My question is regarding the isolation for the ceiling. My original plan was to build two separate joists, one for the interior room (10 feet high), and one for the exterior (11 feet high). Interior ceiling would be like the walls with 2 5/8" gypsum boards and GG. I was planning on doing an additional two layers of gypsum Board with green glue under the joists for the exterior room and sealing the perimeter with acoustic caulk and then putting insulation on top of this between the joists. My fear is this will create a triple leaf effect with the OSB on the rafters (even though it won't be air tight)? If this is the case, how much would it take away from the isolation? Any other cost effective option that you guys would propose to help with ceiling isolation?

Thanks for all your help and excited to be a member of the forum!

Jeff


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PostPosted: Tue Oct 17, 2017 1:52 am 
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Joined: Thu Aug 21, 2008 10:17 am
Posts: 11990
Location: Santiago, Chile
Hi Jeff, and Welcome! :)

Quote:
So goal would be to have around 50-60 db of isolation (not really sure if this is the right way I should express how much isolation I want, but it makes sense to me).
:thu: Exactly. That is indeed, the way to do it. Start with "How loud will I be?" measure in dB, subtract "How quite do I need to be?" (also in decibels), and the answer is how much isolation you need, in dB.

Quote:
using an acoustic drum setup with volumes usually in the 105 db range
Assuming you used "C" weighting and "Slow" response when you measured that on your meter, you are a quiet drummer! That's more like jazz or blues drumming. Full-blown contemporary rock drumming can easily hit 110 BC or 115 dBC, or even more. 105 is not loud, for drumming. But it's still LOUD if you are a neighbor, not the drummer! :)

Quote:
so the overall volume shouldn't increase much.
Right. The dB scale is logarithmic, so even if you managed to make it twice as loud twice as much acoustic intensity going out), with screaming singers and roaring electric guitars, the actual SPL level would only go up by 3 dB.

Quote:
My original plan was to build two separate joists, one for the interior room (10 feet high), and one for the exterior (11 feet high).
Ummmm... This is a ground-up build, right? And you are planning on two-leaf "room in a room" construction, right? so where did the other ceiling come from??? :shock: If you are building a two-leaf room, then the roof and external sheathing of the building ARE your outer leaf, and there's no sheathing on the inner face of those studs and joists. You only need to build a another single leaf inside that, once again with sheathing on only one side of it. So I din't understand where the "two separate joists, one for the interior room and one for the exterior room" are coming from. There's only one ceiling up there: on the inner-leaf joists. That's your inner-leaf, and the roof is your outer-leaf.

Now, if it turns out that you need a vented roof deck, because of the type of roofing that you choose, then that's a different story: in that case you would need an additional ceiling up there, to create the actual sealed mass, and in that case yes, you would have a three-leaf system up there. In which case you compensate for the lost isolation by adding more mass to all three leaves (but mostly on the inner leaf), and by having a larger air gap between the leaves than you would have had if it was just a two-leaf system. You use the usual sets of equations for 2-leaf and 3-leaf construction to figure out how much extra mass you need, and how much extra gap.

This all depends on what type of roof you build, and how you build it.

- Stuart -

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I want this studio to amaze people. "That'll do" doesn't amaze people.


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PostPosted: Tue Oct 17, 2017 6:31 am 
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Joined: Thu Oct 05, 2017 10:33 am
Posts: 6
Location: Houston, TX, USA
Thanks Stuart! That makes perfect sense. I knew I was over complicating things.

I probably play at 105 db in my current untreated room so I don't get the police called on me!!! But in reality, you're right, probably more in the 110-115 db range.

So with regards to isolation for the outer leaf (which will just be the sheathing), I was planning on doing 2 layers of OSB (either 5/8" or 3/4") with staggered seams for the exterior. R13 insulation as well. With staggered seams, I should only need to apply acoustic sealant to the perimeter of each wall plus the roof (from the inside where the stud meets the sheathing) and bellow the bottom plates, right?

From a cost consideration...since OSB is double the cost of drywall depending on thickness, how much of a loss in performance would I get it I went with 7/16 inch OSB instead of the 5/8" or 3/4"? I realize that's probably difficult to quantify exactly.

Also for the green glue, I'm guessing there wouldn't be any issues with applying it on the exterior between 2 layers of OSB? How much of an improvement would you guess I would get with this extra layer of green glue on the exterior between the OSB? Trying to come to a good cost to performance ratio.

Thanks again! :D


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PostPosted: Tue Oct 17, 2017 10:11 am 
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Joined: Sat May 20, 2017 7:47 am
Posts: 291
Location: Surfleet, UK
Hi there,

Welcome to the forum! You sound like you're getting there with your design.
So regarding OSB are you using two layers for a particular reason? You may not know, but you don't need to apply the second layer over the front of the first layer of your exterior walls. You can use plasterboard (gypsum board / drywall) by cutting it to size and attaching it between the wall studs up against the OSB.

Process:
Exterior wall frame is built with 2 x 4 studs.
OSB screwed to the OUTSIDE.
INSIDE the room - caulk along the edges of each stud and soleplate/headplate
Cut plasterboard to 16inch wide and press up against the OSB between the studs. Screw the plasterboard into the OSB. (Get screws that are the right length - ie. wont poke through your OSB)
Caulk the edges of the studs and soleplate/headplate again.

If you were using green glue you would apply it to your plasterboards before screwing them to the OSB.

If you are looking to do the work on a budget, you may be able to achieve your desired transmission loss by additional layers of plasterboard instead of green glue. But that would of course depend on whether you are doing the work yourself and have the time.

Have fun,
Dan


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PostPosted: Thu Nov 02, 2017 7:40 am 
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Joined: Sat May 20, 2017 7:47 am
Posts: 291
Location: Surfleet, UK
Quote:
If you were using green glue you would apply it to your plasterboards before screwing them to the OSB.


After speaking to a sales rep at the greenglue company, they specify that greenglue works best when between two sheets of plasterboard. Using one or both layers as OSB instead will reduce the performance of Greenglue. Also greenglue is not designed for use in exterior applications, that means that they do not recommend it for use sandwiched between the outer leaf layers of walls. The rep said that the temperature variations/extremes are not suitable for greenglue compound and it's performance could be severely affected. The rep recommended use on the warm side of a building walls only (that is, on the inside of any wall insulation like fluffy fibreglass).

The rep concluded by advising that if you want to use it on walls that make up the outer shell of a building with OSB sheathing on the walls, then do this:

Inner leaf only:
Studwork,
OSB3 Sheathing,
(Vapour barrier/membrane if needed in your area of the world)
Plasterboard layer 1,
Greenglue compound,
Plasterboard layer 2.

You'll notice that an OSB wall with green glue compound should have 2 layers of plasterboard on its face to sandwich the greenglue between. The rep also confirmed that Greenglue should not be placed against a waterproof membrane as it works most effectively against porous surfaces and this would likely reduce performance.


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