Basement Studio in Illinois.....

So...does the outer leaf need to be sealed up to the ceiling?

I'm not sure I understand what you mean be "sealed up to the ceiling"? If you mean "Do the outer leaf walls have to be sealed to the outer leaf ceiling and to each other?", then the answer is "yes". Each leaf needs to be completely sealed, hermetically, in order for the MSM system to function properly, and for you to get maximum isolation. Think of it like the two leaves are trapping the air "spring" between them. So each leaf needs to be sealed airtight. I'm not sure if I answered your question, though!

Soundman- If the ceiling joist are sitting on the wall frames...how do you seal the holes that will be created between every cieling joist? Like a lot of "dudes" will be building my walls on the ground and raising them, so I will not be able the plasterboard the walls above wall height to cover....or can I? lil

like this?

Hey Lilith. I can think of at least three ways of doing that. Maybe Brien or someone else can suggest others. #1) Instead of resting the joists on top of the top plates, build your wall a little higher (the thickness of the top plates), then use joist hangers on those top plates, and butt your joists right up to the top plates. #2) Extend the drywall on the walls up to the height of the drywall on the top of the joists. This seems a bit risky to me, since you'd have to be extremely careful not to break the unsupported drywall as you install the joists, but I see no reason why it can't be done if you are careful. #3) Install blocking between the ends of the joists, right where it sits on the top plates. Personally, I like #3, but I think any of these would work. - Stuart -

Soundman2020 wrote:

#3) Install blocking between the ends of the joists, right where it sits on the top plates. Personally, I like #3, but I think any of these would work. - Stuart -

#3 produces the best overall outcome if density, stability and ease of install are being considered. And I am nothing if not easy!

Everyone.... thanks for the great disucssion...Its precisely what I was looking for. Again, I'm totally new to this stuff...could you specify what you mean by "blocking?" thanks again for humoring me.... Jon

... could you specify what you mean by "blocking?"

Pieces of 2x4 (or whatever it is you make your joists out of) cut to the exact length to fit across the gaps between the joists at each end, on top of your top plates. Nail / screw securely in places, seal tightly. Season to taste. Serve chilled... :) In other words, if you have your joists 24" OC, then cut a piece of the same wood about +/- 22" long, so that it fits exactly in the space between the ends of the joists. You could just leave it like that, but since I'm too much of a perfectionist, I think I'd either double up on the blocking, or set the blocking further back in the gap so that I can put in a few layers of drywall on top of it, to try to build up the mass a bit more, otherwise I think the blocking will be your weak point. But that's just my paranoid streak showing through, and it might not be necessary. - Stuart -

Stuart, Thanks again for the info.... Its certainly looking like the existing HVAC is the week point in my current space, since it makes blocking those areas off pretty difficult I think.....

Thanks again for the info.... Its certainly looking like the existing HVAC is the week point in my current space, since it makes blocking those areas off pretty difficult I think.....

I don't see why it would be difficult due to your HVAC: you can do it from INSIDE the room! In other words, once you have the walls and ceilings in place, you can push your blocking into the gaps from inside the room. Stagger nail / screw through the joists sideways, or through the blocking itself, to hold them in place. Caulk. Done! Alternatively, you could do it while you are building the walls: Nail the blocking in place on top of the top plates, before you even put the joists in place. That would mark your joist positions for you, too: there would be a gap in the blocking for each joist. Another alternative: put the blocking in place while you are framing the ceiling: each time you set a joist in place, nail in a piece of blocking next to it. Many ways to skin a cat! :) - Stuart -

Ok....I guess I still don't get it. I'm slow! I've included a diagram, and a skp file for help here. The left opening between joists shows how blocking would occur if there is nothing in between there....simply fill in with an appropriately sized blocking agent, caulk, seal voila. However, the right joist shows how the existing house HVAC passes between the joists. So the room ends, but the HVAC keeps going. I can easily build an inner wall/ ceiling assembly, but I'm still confused on how the HVAC passing through is dealt with from a blocking perspective. the blocking piece on the left wouldn't fit....with out a huge custom drilled hole? This must be an issue in other folks basements, so I'm guessing there is a compromise I'm not seeing. Thanks again everyone!

ps....here's my most current skp file http://www.box.net/shared/ffykuacygq

I thought you were going to build an inside-out ceiling? If not, then you don't need blocking. Also, on your SKP, those pipes are touching the joists for your inner leaf ceiling. Not good. Flanking. Also, your inner-leaf ceiling joists do not go far enough onto the top plate: They should span the entire top plate, I think. Also, you do need joists right at the edge of the walls, just inside the framing of the wall itself. Otherwise you have nothing to nail the edge of the drywall into! - Stuart -

Stuart.... Thanks for the reply...Yes inside-out is still an option. I kind of just threw that SKP together quickly to make a point. I guess the real issue though is that if I successfully contruct an inner room (ceilings/wells) and there is an outside wall (2nd leaf) that stops in the room ( and is not adjacent to a foundation wall), then that wall must be sealed all the way to the top deck (the "ceiling" of the 2nd leaf, which is also the floor of the above living space). However, if existing HVAC runs through the joists past the end of my inne room, then it is impossible to seal the outer layer, right? As for my silly drawings, I am definitley aware of the flanking issues with the HVAC...I'm guessing they'll be switched to fiberglass ducts instead of metal ones. oh gee...i'll do another diagram

Thanks- soundman and Xspace! I've been losing sleep over the ceiling. Great explaination. I'll stop hijacking the thread now. lil