Isolating Footfall Noise Through Floors
Treating sound problems at the source increases the value of the products used because it limits the flanking paths by treating the vibrations before reaching the framing.
WHAT WILL WORK
How to reduce noise between floors in order of highest performing to lowest performing
Comparing the many different types of underlayment that exist, rubber underlayment provides the most significant increase in foot fall noise reduction. The performance of rubber is much higher and consistent when installed over or under concrete, but will perform well in wood structures. The same performance can be achieved in hardwood floor noise reduction if the rubber can compress as intended. With concrete sub-floors, the rubber compresses properly because the concrete has no give. Over wood, the rubber does not typically compress as intended because the wood will allow some give in the structure. Adding about seven pounds per square foot of mass below or above the rubber resolves this issue by stiffening the structure, allowing the rubber to compress. Read Maximizing Rubber Underlayment Performance. An alternative to adding mass over the rubber would be the use of a thicker rubber underlayment flooring sound insulation product or to decouple the ceiling in the assembly. View GenieMat® RST rubber underlayment.
Decoupling the floor is an option now that the Acoustic Sleeper exists. Other similar style products used to decouple floors are not successful because the material is too rigid and requires too much pressure to compress in wood structures. Acoustic Sleeper is well tested though to show high performance with a pretty minimal depth overall (about 1-1/8" plus finish floor). Green Glue Compound can be used in conjunction with the Acoustic Sleeper system by applying the Compound between the two layers of 7/16" plywood used in the Acoustic Sleeper system. View Acoustic Sleeper.
Green Glue Compound in the floor will provide minimal benefit without decoupling the assembly ceiling (resilient sound clips or resilient channel). If decoupling the ceiling, then adding the Compound to the floor between layers of rigid mass can gain as much as 6 STC points and 7 IIC points. View Green Glue Compound tubes or Green Glue Compound pails.
WHAT WILL NOT WORK
In no particular order
Layers of mass floor noise insulation over a resilient material like GenieMat® RST is extremely beneficial in a wood structure. However, additional layers of mass over existing mass without the added resilient layer will provide little benefit in isolating impact footfall noise.
Cork floors, unless incredibly thick (1” or thicker), will not significantly improve the IIC rating of a floor. Cork tests show performance of only about a third as much as rubber underlayment of the same thickness.
These types of underlayment products are often available through local flooring supply stores. The impact footfall ratings advertised by the manufacturers of these products are often well above 60 or even 70. These ratings are not realistic. Foam underlayment will help soften the cushion a little, but the material is not resilient enough and lacks density. So performance gains are often minimal, typically around 9dB in reduced sound transmission.