Super insulating and soundproofing
I’m curious as to whether anyone has integrated soundproofing techniques into superinsulated walls. As mentioned in other posts, I’m considering adding thickness to my existing walls in the form of rigid foam, without removing current drywall. I hear foam is not the best for sound, although at least the 3/4″ airspace and second layer of drywall will help. I’m curious if anyone else has explored trying to get the best of both worlds, R-value and sound reduction, while keeping thickness to a minimum. I’m under a major flight path, and since I’m touching everything else, I figure why not design in some exterior nois reduction.
I’m familiar with the 4 primary ways to reduce sound (mass, damping, isolation and absorbtion), but these don’t always mesh with high R-value per inch insulation techniques. I thought it might be a good idea to use green glue between layers of foam and drywall, but I don’t know if that would acomplish anything since there is so little mass. I also know I could easily add a second new layer of sheetrock with green glue to shear dampen the two mass layers. Is this the best approach without having to increase thickness much further? Is it better to have the damped layer buried in the center of the wall, or on the occupancy face of the rigid foam?
Thanks,
Ryan Griffin
1450SF 1.5 story
Minneapolis, MN
climate zone 6
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Replies
Ryan, Adding individual elements to a wall or ceiling can act in unexpected or counter-intuitive ways.
If you look at rated wall assemblies for example you will see that adding a sound absorption board to the middle of a double stud wall will reduce its STC rating. Similarly strapping an existing wall and adding a double layer of drywall will do the same thing.
To get predictable sound attenuation results your best bet is to closely mimic a complete rated assembly. You can find hundreds of assemblies just by Googling. You should be able to select one which closely mirrors what you would also like to use for energy efficient reasons.
Malcolm,
Thank you very much for the tip. I've found some of this information helpful, such as isolation of a double wall. Unfortunately, I don't see much of anything regarding insulation types, especially foam insulations which offer the best R-values per inch. I will keep looking, but if anyone can point to the best source for this sort of info, that would be appreciated.
Another answer that's not what you were looking for, but mineral wool is worth considering for its combined sound and thermal isolation capability, and is sold for both purposes.
Ryan, Poking around I can't find any reliable numbers either. I assume this relates back to my first post: Isolated materials are not tested, assemblies are. You may find comparable walls with different cavity insulation, which would give you some idea, but as a general rule of thumb foam does not perform as well as mineral wool but has the advantage of air sealing and eliminating pathways for flanking sound often neglected in wall and roof assemblies.