What to do with back (outside) of room in room walls??

Hello everyone. To reiterate - I have read Rod's book, but could not find this topic discussed either (As per my last post) I finally got a drawing together of what I'm looking to do with my building (see attached - crude I know). First of all, I'm located in Michigan. Secondly, I hope that most of my notes on the drawing make sense to everyone. What I'm wondering, is if I angle the walls (needed to make access for mechanical room per local code and to break up parallel surfaces - duh), and am left with a large void (ranging from a couple of inches to 30" at the largest spot), can I actually put drywall on the back (outward facing) of my room in room design (yes I know - creating a triple leaf), or leave the drywall OFF the outside of this wall and fill the void with an extreme amount of insulation or other material? Thanks again for all of your help. Brian

If your exterior walls are concrete, explain this: "Live Room is a Room in Room design of Staggered wood 2X6 construction." Your exterior is the first barrier for a room-in-a-room, the interior wall being the second. If you have a mechanical room, code is going to want a fire rated partition and quite possibly proper venting if you have gas/ open flame. I think that local code is going to dictate how you do this, which may well wind up being a multi leaf.

Thanks Xspace I must tell you, your comment of: "Your exterior is the first barrier for a room-in-a-room, the interior wall being the second" is such a straight forward and simple answer to this question (and I've seen this question posted on many discussion forums). Thanks so much for the answer. My design is now three out of four walls with two layers of 5/8 + GG and ample air space + insulation, then the exterior walls are concrete block (of my building) and brick on the older buildings attached. The 4th wall is a staggered design with 2 layers of 5/8 and GG on one side and one layer of 5/8 on the other. There's a large airspace (up to 30" for code reasons) then the exterior block wall has been sprayed with foam for a vapor barrier (I understand that this has virtually no STC properties) Thanks again. The project is coming together... Brian

loftdweller wrote:

"Your exterior is the first barrier for a room-in-a-room, the interior wall being the second" is such a straight forward and simple answer to this question

Well, it only applies to your situation since you have a single leaf concrete barrier. If the exterior of another project was wood framed with material on both sides of the wood studs, then that would be different entirely and would not be as simple. Good luck, Brien

Please make sure to check your local code on the foam. You will not want exposed foam in a furnace room as it is flammable and the fumes can be toxic.