John Sayers' Recording Studio Design Forum Archive

Hey guys, I can't find the answer to this anywhere, it may be silly but I tend to obsess over details so...

Building and inside out wall system, I build the outer leaf and fill the 2x4 stud cavities on it with 5.5" thick insulation. I now place my inner leaf, inside-out wall, with a 2" space between outer leaf floor plate and inner leaf sheating. That makes the insulation rest against the inner leaf heating with no compression, and completely fills the air gap with insulation like everyone says to do. The question is, should anything be done on top of the outer leaf studs? Since the insulation is in the bays, there will be a gap 1-1/2" wide (stud size) and 2" from the Inner leaf sheating every 16 inches (stud spacing). Do I need to try and fill the cavity completely? Or is that gap over the studs acceptable? I've attached a picture of what I'm talking about for clarity. Hopefully this makes sense. Thanks in advance.

-Scotty

Hello Scotty,
Forgive me if I haven't grasped your question, but are you asking if the gap between your inner and outer leaves should be partially or completely filled with insulation? I would say fill completely - as I understand it, any cavity between the inner an outer leaves should be filled unless it's a door, window or HVAC vent. Hope this is helpful, John.

Yes, so the difficulty is once the inner leaf is constructed you cannot access the cavity in order to completely fill it, correct?

I wouldn't worry about it, it's going to be pretty much totally full and the little areas where the studs are not covered are not going to matter in the grand scheme of things.

Just as a side note, make sure you only use low density (low GFR) fluffy insulation inside the cavity, rigid and semi dense are not only over kill but could actually couple the two leafes at certain frequencies.

If you wanted to be a complete perfectionist about it then you could always lay another layer of insulation across the studs before you construct the inner leaf - simply hold it in place with large washers and screws screwed into the studs.

Looks like you may have done this in your picture, but for anyone else reading - the other thing to remember is it is better to stagger the studs between the outer and inner leaves, so the studs are not opposite each other. Just a small detail but it helps to increase isolation, in theory, as it breaks up the waves some more as they try to pass through the assembly.

Paul

Thanks for the response Paul! I kinda figured it didn't matter, but I wanted solid clarification. And yes! I knew about the staggered studs. Almost ready to start building. (At least until the next detail pops up.) Thanks!