Posted: Mon Jan 31, 2005 11:26 am
No, you're right - 2.5 pcf stuff is optimum for almost ANY place in a studio where you would use insulation, either in or outside of a wall or ceiling. If that's what you have, and you can get it to "come out even", as in, complete fill with slight overfill (only enough overfill to require slight pressure against the first layer enclosing the insulation, in order for the wallboard to contact the frame) - then, you're set.
If, however, another layer of the Roxul would cause moderate to heavy compression of the insulation, then you will need to get some UN-faced, normal density, house insulation to make up the difference if you want the best isolation you can get with your particular combination of joist depth, layers, etc. -
If you're NOT concerned with max isolation for some reason, you can just put the batts into the joist cavities and install the ceiling layers - gravity will damp the lower panels, the extra wallboard layers between joists will lower the resonant frequency of the upper leaf, and it will cost less for insulation.
The main loss of doing it the second way, will be increased footfall noise from movement above you, although it would also lessen overall TL through the structure a slight amount as well, same as in a wall... Steve
Overall, the best performance will be by using as much of the 2.5 pcf stuff as you can, making up the difference with lighter stuff for panel damping - the lighter stuff should go into the cavity first, so it ends up on TOP of the heavier stuff and will therefore compress less, staying in better contact with the upper panels.
From no insulation to nearly filled is the most change in performance; likely around 10 dB or so. The extra I'm referring to will not make a lot of difference in overall TL, but will lessen any ringing at resonance so the room will sound flatter in response.
If, however, another layer of the Roxul would cause moderate to heavy compression of the insulation, then you will need to get some UN-faced, normal density, house insulation to make up the difference if you want the best isolation you can get with your particular combination of joist depth, layers, etc. -
If you're NOT concerned with max isolation for some reason, you can just put the batts into the joist cavities and install the ceiling layers - gravity will damp the lower panels, the extra wallboard layers between joists will lower the resonant frequency of the upper leaf, and it will cost less for insulation.
The main loss of doing it the second way, will be increased footfall noise from movement above you, although it would also lessen overall TL through the structure a slight amount as well, same as in a wall... Steve
Overall, the best performance will be by using as much of the 2.5 pcf stuff as you can, making up the difference with lighter stuff for panel damping - the lighter stuff should go into the cavity first, so it ends up on TOP of the heavier stuff and will therefore compress less, staying in better contact with the upper panels.
From no insulation to nearly filled is the most change in performance; likely around 10 dB or so. The extra I'm referring to will not make a lot of difference in overall TL, but will lessen any ringing at resonance so the room will sound flatter in response.