acoustical sound underlay, hardwood flooring sound barrier
Noisy neighbors and hard surface flooring don't mix. 

You can, however, reduce noise transference by using 'sound absorbing underlay' for floating hardwood or laminate floors.

Here are some general points about sound-absorbing underlays that may help you with your purchase decision:

Make sure that the underlay you choose has been tested using ASTM International (formerly American Society for Testing and Materials) standards .  Ask for paperwork that substantiates the underlay manufacturer's claims of the product's sound absorbing qualities. The product should have been tested in accordance with ASTM E-492.

The test results should show a couple of things....

1. An IIC (impact insulation class) rating
This is the number used to rate the sound absorbing characteristics of the underlay when noise produced from a test impact is measured.  The higher the rating the better the product is at absorbing sound.  Most products on the market have an IIC of between 60 and 75.

2. An STC (sound transmission class) rating
This measures a building material's (in this case underlay) ability to absorb audible noise such as voices or TV sound.  Most products on the market have an STC in the high 60's.

I tell my customers that 90% of the noise problems in condos exist because of lifestyle.  If you have a noisy lifestyle, then your neighbors will hear you. There is not a sound absorbing underlay on the market that is going to stop clacks and bangs, or noise from loud TV's from transferring through walls or wood flooring to neighboring suites.  Yes, a high density foam underlay with a good IIC rating will reduce the noise transference but it will not eliminate it. 

With this in mind, strata councils or building managers put rules in place (by-laws) that require a high IIC rated underlay be used for any new wood or laminate floor installations.  By doing this, they can say they made a reasonable effort to keep noise transmissions to a minimum should there be a complaint.

In some cases, just to keep the peace between neighbors, by-laws go further and demand that for example, 60% of the new hardwood or laminate flooring be covered with area rugs.  If you've ever lived beneath noisy people who have hardwood flooring you will understand why.

My advice....keep it simple.

1. Check your building's by-laws regarding sound barrier and IIC / STC requirements for hard surface flooring before installing your new floor.  In this case, it's better to ask permission than beg forgiveness!

2. Set expectations - living creates noise!  If you have a couple of active kids, play the piano, wear shoes that clack on the floor as you walk around the apartment, walk with heavy foot falls, you drop things, you like your stereo or TV sound turned up louder than most - then you are going to be heard by your neighbors.

3. Use area rugs to help reduce noise.

4. Do not nail wood flooring to an acoustical underlay.  This allows for too much movement in the wood floor pieces and will likely lead to squeaks and gaps.  Also, nails or staples facilitate sound transference similar to that of a tuning fork.  If you are nailing the flooring to a wooden sub-floor and want to insulate against sound transmission, then you will need an altogether different kind of sound barrier system - it's time to consult an architect or experienced builder.

If you live in a wood frame building with no acoustical concrete topping between floors, a sound absorbing underlay with the highest IIC rating, will not prevent sound transference.  Most underlays achieve their IIC and STC ratings from testing over concrete sub-floors. Wood frame construction and plywood substrates are notoriously bad at muffling sound and none of the products that I know of on the market are going to change that.

Hi-rise concrete buildings are best for natural noise containment because concrete is a great sound barrier.  Most hi-rise construction consists of 6" to 8" of concrete sub-floor between you and your neighbors below.

With all this said, a few underlay recommendations that are readily available and that I consider to be good value sound barriers for a floating floor installation are:

1. Dura-son
2. Sound Blocker
3. Floor muffler
4. Cork

There are many more on the market to choose from.  Check that the IIC and the STC ratings comply with your bylaws, and make sure that the IIC rating given to the product was gained using ASTM E-492.