Found this that may be of some interest.

http://www.stcratings.com/assemblies.html

I am guessing my wall plan of 5/8 on channel with an insulated staggered stud wall will net me an STC at or near 50db. I think the weak link in my dividing wall will be the french door with a large glass area in each. Might look at custom making doors with spaced double panes. Prehung french doors would be so easy though....

Hey Nick, did you ever get your cooling scenario figured out? I stumbled on your thread while trying to find cooling and air turnover specifics. I'm thinking I may put a thermostat controlled motorized damper inline ahead of the main and second floor tee-off point. My thoughts are that if the room gets too hot outside air will be pumped in and out at the full CFM the HRV can muster. Theoretically, at max would turm the room over just over three times an hour. Hopefully its enough..... A dead vent will add another weak link in my wall. frown

New HRV and whole house replacement windows showed up friday (old ones were single pane when we bought eek ) Installed 5 windows today. HT on backburner... again. Poo.