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PostPosted: Thu Oct 18, 2018 2:28 am 
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Joined: Wed Oct 10, 2018 4:17 pm
Posts: 6
Location: London, UK
Hi folks.

I'm currently planning a studio/rehearsal place. The concrete base is done and the timber ready to start framing the build, which is 6m x 4.4m.

It shall be requiring only moderate isolation, although the more I can get without much cost, the better, obviously. It will be built from 2x6 timber framing with 2 layers of 15mm PB (drywall) with GG between. Within the 6" cavity, will be insulation - I'm still researching whether to use fluffy cheap type or the expensive acoustic slab type.

It will also have a layer of 18 OSB to help stiffen the timber building, and add extra mass for isolation. The timber frame will be covered outside by 9mm cement fibre cladding sitting on 25mm battons .

Im having difficulty determining whether this cladding (hardieplank / marley cedral /etc) will count as a layer. I'm sure I read somewhere that it wouldn't count as a layer as it wasn't anywhere near airtight, but then I recall reading somewhere else that it WOULD count as a layer, despite the airgaps.

Obviously this will dictate where I place my OSB. If the cement fibre cladding counts as a layer, and I place the OSB sheathing on the outside of the timber frame (which appears to be the standard building practice from what I can tell), I will end up with triple layers.

If the cladding doesn't count as a layer, I believe I will gain extra isolation by having the OSB and 2xPB on separate sides of the framing.

Following on from this point, the ceiling won't have a layer of OSB so is there actually anything to gain from having it on the walls?

I'm actually a bit confused on my ceiling. Again, 2 layers of PB but I don't see what I can do to increase isolation after that?

If anyone can shed some light of my confusion, I'd be very grateful.

I looked through the forum trying to find some similar builds to gain knowledge, but sadly there appears to be a lack of shed-based studios. If anyone can point me in the direction of any previous builds similar to what I'm proposing, that would be awesome.

Thanks guys.


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PostPosted: Thu Oct 18, 2018 10:19 am 
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Joined: Wed Feb 01, 2017 6:03 pm
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Location: St. Albert, Alberta, Canada
Quote:
I'm currently planning a studio/rehearsal place.

Okay, so rehearsing is usually quite loud, unless you're an acoustic guitar player singer/songwriter. What sort of instruments will you have rehearsing? The word "studio" implies recording. Recording typically implies requiring a low noise floor (unless you're recording super loud metal genre drums or guitars maybe).

Quote:
The concrete base is done and the timber ready to start framing the build, which is 6m x 4.4m.

I'm glad you posted on the forum to make sure you have a plan of a attack BEFORE starting framing! You should have a complete 3D model of your build done before you start framing. It actually blows my mind that people build any structure without doing this first.

Quote:
It shall be requiring only moderate isolation, although the more I can get without much cost, the better, obviously.

What is "moderate" to you? We need a value here. Take a slow, C weighted measurement with a real meter outside where your building will be and figure out what the background noise level is. If you tell us what instruments you will have rehearsing, we can probably figure out how much transmission loss your structure needs to provide. Also, tell us what your municipality laws state for SPL levels at your property line. Let us know how close your building will be to your property line. You need to make sure you hit those target levels or else you may face some issues in the future.

Quote:
It will be built from 2x6 timber framing with 2 layers of 15mm PB (drywall) with GG between. Within the 6" cavity, will be insulation

I'm not trying to be a smart ass by asking you a question instead of telling you some theory, but here I go:
Why do you figure you should build it like that? What are your target TL values? How did you figure out that this wall configuration will give you those values? Show us the math please.

Quote:
I'm still researching whether to use fluffy cheap type or the expensive acoustic slab type.

You totally can. Just make sure it is 20-25 kg/m^3

Quote:
Im having difficulty determining whether this cladding (hardieplank / marley cedral /etc) will count as a layer. I'm sure I read somewhere that it wouldn't count as a layer as it wasn't anywhere near airtight, but then I recall reading somewhere else that it WOULD count as a layer, despite the airgaps.

I wouldn't count it as a layer because it barely makes a connection to the rest of your sheathing. This stuff is breathable behind it. For your calculations and planning, I would say to ignore the fact that it's even there. Consider it aesthetics only.

Quote:
Obviously this will dictate where I place my OSB. If the cement fibre cladding counts as a layer, and I place the OSB sheathing on the outside of the timber frame (which appears to be the standard building practice from what I can tell), I will end up with triple layers.

Are you mixing up the terms "layer" and "leaf"? I'm kind of confused with what you're writing as I'm questioning which you're referring to. Triple "layers" are a good thing. Triple "leafs" are a bad thing.

Quote:
If the cladding doesn't count as a layer, I believe I will gain extra isolation by having the OSB and 2xPB on separate sides of the framing.

Correct.

Quote:
Following on from this point, the ceiling won't have a layer of OSB so is there actually anything to gain from having it on the walls?

You must ensure that your ceiling or roof maintains the same density as your walls, otherwise whichever has the least isolation dictates your total isolation. If your ceiling provides you with 15dB of transmission loss, then your whole shed will only have 15dB.

Quote:
I'm actually a bit confused on my ceiling. Again, 2 layers of PB but I don't see what I can do to increase isolation after that?

If anyone can shed some light of my confusion, I'd be very grateful.

I looked through the forum trying to find some similar builds to gain knowledge, but sadly there appears to be a lack of shed-based studios. If anyone can point me in the direction of any previous builds similar to what I'm proposing, that would be awesome.

It appears as though you are just aimlessly putting two layers of drywall up on your walls because that's what you've seen some one else do. You haven't stated your required isolation levels.

From what I can see, you're probably going about this incorrectly. Your current plan is a coupled 2 leaf wall. Basically a slightly beefier version of a normal wall in your home. Let's talk about this. Providing you can actually get your ceiling to perform the same as your walls (that would require an air tight outer leaf with the same mass as your walls), you will achieve about 4.5-5 dB more isolation than a typical wall in your house. We all know that a normal wall does virtually nothing against the loud volumes of guitar amps and drums. Here is an image to show you what's up:
Attachment:
Typical House Wall IR-761--page-23--STC-34.jpg

You can see from about 200 Hz down, it's providing very poor isolation.

Now, it's a fact that in order to obtain a theoretical 5 dB more of isolation, you need to double the mass on your walls. So, if you put two layers of sheathing and drywall on your wall, you're going to get a theoretical 5dB improvement. In practice though, this is a smaller number. That's why I said you'd be lucky to achieve a 4.5 dB increase. This isn't much. It's still in the realm of "bad".

So, to conclude my point, IF the instruments your rehearsing with are loud. Or if the instruments you're recording are quiet, you probably need higher levels of isolation than what your current design will provide. The cheapest, and frankly, best solution is to build a room in a room. This will give you great results. I'm just finishing up version 2 of my transmission loss calculator which will allow you to see the levels of isolation you can achieve with this method. Here's a screenshot of it in it's current state where it has two layers of drywall on each side of the leaves (same as your current design), except it has a 2x4 wall framed 1" away from the outer leaf wall. So, the only difference between this design and yours is that it has 2x4 dimensional lumber added into the equation. Not much extra money. Look at the results:
Attachment:
MSM Ver 2 example.png

So, where your design is offering a PEAK TL of around 55dB for a very narrow band, and the rest averaging (the purple line) around ~32dB. Also, below 200Hz (the problematic area), you're average is about 16dB, you could add a 2x4 frame and lose a total of 4.5" around your room and achieve these results. To look at these results, we can conclude that your average TL would be about 60dB. HOWEVER, this isn't really accurate because the troublesome frequencies live in the lower cycle region. That's where this design shines. You can see on the chart that we drop from the ~70dB range around the 200Hz region. However, at that frequency, we have a gradual decrease of efficiency from ~70dB tapering down to an amazing 53.8dB at 31.5Hz. Yes, 31.5 Hz. Amazing. Granted, this formula is an approximation for those frequency ranges, at least it shows us the drastic difference in the lower frequencies between a coupled and de-coupled wall system.

On the other hand, if you stuck with your system, to get these sort of results you'd need to double your mass over and over and over (example: say you have 4 layers of drywall -- if you want to gain another 4.5 to 5 dB of isolation, you'd need to go up to 8 layers of drywall, then double again to 16, then 32, etc).

I hope this helps!

Greg


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