As New York green contractor we feel that unwanted sound can be just as toxic as chemicals so we put a lot of work into making homes that reduce sound. We are in the soundproofing stage of our Passive House renovation in Harlem. Here the soundproofing techniques we used:
Foam on the joists – foam strips on the joists below the subfloor.
Cotton layer on the subfloor – we rolled out a layer (or two) of recycled cotton mats between the subfloor and the floor
Staggered Studs – the wall studs are staggered so that the sheet rock on one side is not in direct contact with the sheet rock on the other side, essentially breaking the path of sound.
Green Glue – we put green glue between two or three layers of sheet rock.
Sheet rock off the floor – we left a 1/4″ inch gap between the floor and the sheet rock, which we then filled with sound proofing caulk.
Electric outlets – we never put an electric outlet in a wall stud if there was another electric outlet in that wall stud for the other side of the wall to reduce sound passing through the holes of the electric outlets.
Where we had to share the stud bay with two outlets we wrapped the electric box with sound proofing putty.
We put salvaged fiberglass insulation in between all floor bays, under the stairs and in the wall studds.
We caulked all the tread and riser seams under the stairs.
We lined all duct work with insulation.
The list seems like a lot of work, and it is, but it does wonders for sound attenuation.
Here is a great site that shows the different sound attenuation of different products. You will notice that stone wool is much better at stopping sound than typical fiberglass bats, which is still good. With this in mind we may try to get some and finish off the Harlem job with stone wool instead of fiberglass.
Below is a pic of the salvaged insulation between the floors. Between floors you don’t need insulation for heat, so the insulation is entirely for sound attenuation.