?Which batt type insulation will give me the best soundproofing?? I hear this question a lot, or better still, ?Do I need to add more soundproofing if I already have insulation in the walls and ceilings?? Keep in mind that any batt type insulation, though it may be a great thermal insulator, is generally not very good as a soundproofing agent. If batt insulations such as fiberglass insulation or Icynene were effective soundproofing products, the big boys like Johns Manville ? and Owens Corning ? would take over the soundproofing industry and leave the real professionals out in the cold. Luckily knowledge is still power and it will be a while before all the soundproofing companies are put out of business.
If you are serious about soundproofing always consider batt insulations as the proverbial ?icing on the cake?. They simply don't have the horsepower to be stand alone soundproofing agents such as lead, closed cell foam and mass loaded vinyl.
There are some good sound batt insulations on the market today, one is Roxul AFB? (acoustic fire batt). Roxul? is a rock wool that is made up of mining slag Canada that is hit with high pressure air thus giving it the properties of a very dense fiberglass insulation and while it will provide the end user with an R-13 for the 3 ?? variety and an R-19 for the 5 ?? batts, it's main function in life is to provide superb sound absorption and structural dampening of wall and joist cavities. It is a know fact that damping a structure; especially a wooden structure helps to control the transmission and vibration of sound through said structure.
Bonded Logic?, a company in Arizona also provides a cotton sound batt insulation that is great for filling voids and cavities where sound control is essential. The cotton is an inert material that absorbs sound but does not transmit through its fibers like fiberglass insulation does.
Fiberglass insulation is one of the worst for soundproofing agents out these. It actually transmits sound through its very fibers thus causing the annoying noise to appear amplified. If you are forced to use fiberglass insulation make sure it is isolated from either the sub floor or the ceiling below. Never pack fiberglass into cavities or voids. By isolation the fiberglass insulation from the sub floor above or the ceiling below you will break the sound transmission circuit from the floor above to the ceiling below. The same applies to walls; if the fiberglass insulation is touching one side of your drywall, make certain that it does not come in contact with the other side of the drywall. This makes perfect sense once you know the nature of fiberglass insulation.
To sum this up, never count on any batt type insulation to be your stand-alone soundproofing agent. You will always need the horsepower of lead, mass loaded vinyl, closed cell foam, or of course my favorite, Green Glue?. You can read about these great soundproofing agents in subsequent articles throughout the Internet. For now, this is Dr. Bob, The Green Glue King, signing off and may all of your soundproofing journeys be smooth ones. This is Dr. Bob....Out!!!