Question about room within a room isolation

[javamad]

Hi All,

I am looking at building a 2-room studio in a 1000 ft industrial unit. The unit is detached/standalone so I have brick walls on all sides and a standard industrial corrugated perspex roof. I *think* I should be ignoring the existing roof from an isolation perspective as it has very low mass, so I *think* I should be doing a single leaf wall and a double leaf ceiling to my interior build. However I suspect I must be doing it wrong because for example if it rains ... will the noise from the rain not get into the air gap between the wall leaves and so be heard inside the studio?

In the attached simple diagram I am trying to explain. My question is simple; Will sound wave A that comes through the roof and gets into the airgap between the brick wall and my partition not reduce my overall isolation by quite a substantial amount?

If so ... is there a solution without having my partitions touch the wall?


Many thanks for any help clarifying

[Soundman2020]

will the noise from the rain not get into the air gap between the wall leaves and so be heard inside the studio?

Yes, it will. And sound going out through your inner-leaf wall would also be heard outside the building, via the same path.

Will sound wave A that comes through the roof and gets into the airgap between the brick wall and my partition not reduce my overall isolation by quite a substantial amount?

Correct.

is there a solution without having my partitions touch the wall?

Yes. The solution is to build a proper two-leaf system for the ceiling/roof, in exactly the same manner as for the walls. What you are showing does not accomplish that.

You do not have a complete outer leaf in your diagram: You have only outer-leaf walls, but no outer-leaf roof. So you need to build one. You need to add a "roof" (or "ceiling" if you prefer) just below the perspex sheeting that you have there right now, and it needs to fully complete the outer-leaf enclosure around the space where you will build your inner-leaf room.

- Stuart -

[javamad]

You do not have a complete outer leaf in your diagram: You have only outer-leaf walls, but no outer-leaf roof. So you need to build one. You need to add a "roof" (or "ceiling" if you prefer) just below the perspex sheeting that you have there right now, and it needs to fully complete the outer-leaf enclosure around the space where you will build your inner-leaf room.

I see. So that ceiling would touch the outer leaf walls as it's the outer leaf? If thats the case I think I understand now. I was putting the two ceiling leaves sitting in the inner wall leaf.

Thanks,

[Soundman2020]

So that ceiling would touch the outer leaf walls as it's the outer leaf? If thats the case I think I understand now. I was putting the two ceiling leaves sitting in the inner wall leaf.

Right! Since the roof you have up there now isn't sealed and doesn't have much mass anyway, it's not going to be any use as your outer leaf. You need something more massive (heavier, higher surface density) to complete your outer leaf. That new "ceiling" can only touche the existing outer leaf, and cannot touch the new inner-leaf at all.

Yes, that will create the dreaded "three-leaf system", but in reality it's not a big deal in your case. The effect of the existing "roof" is not very great, as it doesn't have much mass and will be quite a distance away from the "middle" leaf that you will be adding here. As long as you put enough mass on that new middle-leaf ceiling, you'll be fine.


- Stuart -