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Roof for brick shed
Old 18th October 2019
  #1
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Roof for brick shed

Hello all - i'm looking towards building a room-within-a-room in my fairly large brick shed - with a view to isolation primarily.. (size approx two-car garage)

However, the current roof, which is flappy thin wavy metal, needs replacing as the wood that supports it has rotten as some clown put the screws in the troughs rather than the hills, and well, the elements have rotted all the wood.. in short it looks like it was roofed long ago by 'that'll probably hold' folks in a hurry..

It's a low angle single pitch, ie it slopes gently down from one side of the shed to the other.. uk midlands so not huge snow load..

Given that I'm going to want to redo that roof, and I'll be having sound isolation in mind, can anyone point me to some resources regarding designs/practicalities for such a roof?

I'm hoping the structure (single-width brick) can take a little more weight.. but perhaps not an awful lot. I'm interested in what approaches are taken to sealing for sound, e.g. at the edges

I expect that if I want useful mass hanging there then I'll have to get some kind of engineer involved so that nobody gets killed, but i'd like some idea of what proper design approaches might be.
Old 18th October 2019
  #2
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The shed needs a roof as heavy as the walls.
The room within a room needs a roof as heavy as the walls.
But maybe you should first specify what kind of brick is used to construct the shed, how high the shed is and how much sound reduction you need.
What are you going to do in that room, how far away are the neighbours located.... you catch my drift
Old 18th October 2019
  #3
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Yeah, the walls are standard red brick (uk). Clearly the roof will be the weakest link, there won’t be any budget to reengineer for bearing a lot more weight, and i’ll have to make the inner leaf structure do the lion’s share of the mass/isolation work.

I’m think a certain thickness of osb will be as heavy as i can reasonably go for the roof. I’m curious how folk go about sealing a wooden roof structure to a brick wall.. just lots of cement?
Old 18th October 2019
  #4
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I’m inclined to build as good as I can afford, and then we’ll see what that allows me to get away with.. certainly i want to be able to sing freely, beyond that if i can turn amps up to x in the day, y in the night, then fair enough. Same for drumming.. I don’t do much of that. It’s just for me really, to get me out of the house where i can’t get away with f**k all
Old 20th October 2019
  #5
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Here's some images of the metal roof, and dodgy wood..
Attached Thumbnails
Roof for brick shed-img_6060-1-.jpg   Roof for brick shed-img_6061-1-.jpg   Roof for brick shed-img_6062-1-.jpg   Roof for brick shed-img_6063-1-.jpg  
Old 21st October 2019
  #6
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As Bert said, it would help if you could provide more information on what you are trying to achieve here. Such as what the room is for, what the dimensions are, and how much isolation you need.

The basic principles of isolation are fairly simple: It is only as good as the weakest link. If your roof is the weakest link, then sound "escaping" will pretty much ignore the good isolation from the walls, and exit through the roof... into the neighborhood. So, if you need sort of good isolation, then you need lots of mass in your roof deck. If you need more than "sort of good", then the best solution is "room-in-a-room" construction (which you already mentioned), because a single layer of mass on your roof still won't get you a lot of isolation. For example, if you were to put up a layer of 3/4" plywood for your roof, with asphalt shingles on top, very well sealed, then that would get you about 25 dB of isolation, with luck. So if you were planing to play drums in there, the sound level outside would be around 90 dBC. If you were planning to sing loudly inside, that would be heard at maybe 55 dBC outside. If you then do an inner-leaf room inside that, with substantial mass on the inner-leaf, then the weak spot is still the roof, but you could probably expect an additional 10 to 20 dB improvement in isolation, with careful planning and careful construction.

- Stuart -
Old 21st October 2019
  #7
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Hi Stuart - yes i'm looking at room-in-a-room, without a doubt, and I reckon I understand it fairly well, and I know that the lion's share of the mass will have to be on the inner leaf, and I'll keep the gap between the leaves relatively large - this is because I suspect I'll struggle to get more than a layer of EPDM on OSB (and paint) for the roof of the outer shell supported without major engineering. I'm not going to go for specific db reduction figures - I'd rather just keep watching for weakest-links and best practices with a cheapness, and see where it gets me, which will be better than where I am now.

I think my main question here is how would you folks go about sound-sealing a wooden or metal roof to the (brick) walls.. Not a single book I have on studio construction seems to mention it. The existing structure is pretty 'makeshift'.
Old 21st October 2019
  #8
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Quote:
Originally Posted by mutetourettes View Post
Yeah, the walls are standard red brick (uk). Clearly the roof will be the weakest link, there won’t be any budget to reengineer for bearing a lot more weight, and i’ll have to make the inner leaf structure do the lion’s share of the mass/isolation work.

I’m think a certain thickness of osb will be as heavy as i can reasonably go for the roof. I’m curious how folk go about sealing a wooden roof structure to a brick wall.. just lots of cement?
If you use EPDM there is EPDM-sealer.
Old 21st October 2019
  #9
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One thing you should be aware of, is that you won't be able to accurately predict the isolation of your system: the equations for doing that assume that the mass of each leaf is fairly consistent, and that the mass on the inner leaf is roughly similar to the mass of the outer leaf. If there's a large difference in surface density, the equations won't give you the correct answer. In other words, if one mass is a 6-inch thick concrete block and the other is a piece of paper, obviously the equations won't produce correct results. If they are both 2 layers of drywall, they will be quite accurate. In your case, if you put huge amounts of mass on your inner-leaf ceiling and just a thin, light deck for the roof, that's skewed quite a bit.

Quote:
I think my main question here is how would you folks go about sound-sealing a wooden or metal roof to the (brick) walls.. Not a single book I have on studio construction seems to mention it. The existing structure is pretty 'makeshift'.
First, seal the brick. Use a quality masonry sealer all over the inner surfaces. Then, once the roof desk is completed, use backer rod to fill in the gaps as much as possible, and a really good quality caulk that sticks very well to both masonry and also wood (assuming you do an OSB roof deck). Buy several different brands of caulk, and test them all on samples of the same brick and wood, so see which one gives you the best result. Use a caulk that remains flexible and soft after it has cured. And seal the hell out of it! Don't be shy with the quantity. But build it up in layers: first put one thick bead as deep as you can in the gap, then wait for it to cure. Add another bead, ditto. It needs to be thick to build up the mass. The density of caulk is nearly three times the density of OSB, so as long as you get it at least one third the thickness of your OSB roof deck, that will keep the mass consistent. In other words, if the OSB is 3/4", then you need at least 1/4" deep caulk in the gap, to get the same surface density. That's the way I would do it: others might have a different take.


- Stuart -
Old 22nd October 2019
  #10
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Quote:
Originally Posted by Soundman2020 View Post
One thing you should be aware of, is that you won't be able to accurately predict the isolation of your system: the equations for doing that assume that the mass of each leaf is fairly consistent, and that the mass on the inner leaf is roughly similar to the mass of the outer leaf. If there's a large difference in surface density, the equations won't give you the correct answer. In other words, if one mass is a 6-inch thick concrete block and the other is a piece of paper, obviously the equations won't produce correct results. If they are both 2 layers of drywall, they will be quite accurate. In your case, if you put huge amounts of mass on your inner-leaf ceiling and just a thin, light deck for the roof, that's skewed quite a bit.

First, seal the brick. Use a quality masonry sealer all over the inner surfaces. Then, once the roof desk is completed, use backer rod to fill in the gaps as much as possible, and a really good quality caulk that sticks very well to both masonry and also wood (assuming you do an OSB roof deck). Buy several different brands of caulk, and test them all on samples of the same brick and wood, so see which one gives you the best result. Use a caulk that remains flexible and soft after it has cured. And seal the hell out of it! Don't be shy with the quantity. But build it up in layers: first put one thick bead as deep as you can in the gap, then wait for it to cure. Add another bead, ditto. It needs to be thick to build up the mass. The density of caulk is nearly three times the density of OSB, so as long as you get it at least one third the thickness of your OSB roof deck, that will keep the mass consistent. In other words, if the OSB is 3/4", then you need at least 1/4" deep caulk in the gap, to get the same surface density. That's the way I would do it: others might have a different take.


- Stuart -
Hi Stuart - thanks for both parts of your answer - I wasn't aware that skew between the two masses would break the calculations or that the equations 'assume' 'similar' mass.. ho hum... well... I don't imagine i'll actually be doing many equations but I suppose if a thin leaf can't be helped then still the benefits of increased gap and increased mass on the other leaf aren't entirely removed.

Thanks very much for the practical tips around the brick-wood caulking!
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