Cork vs Carpet STC ratings

Q: We are going to replace the flooring in our condo apartment in the near future. A floating cork floor system is our preferred choice but the condo’s rules are that carpet over padding must be installed for sound transmission suppression to adjoining units. However, they are not specific about what kind of carpet and underlayment must be used. I can’t help but think there are some lower quality carpet and underlayment systems out there that are no better or even worse in control sound transmission than a high quality floating cork floor system .
Is this correct and what are those carpet and cork systems that I could compare?
The folks on the condo’s board of directors seem to be reasonable and I think approval for the cork floor could be obtained with the right set of facts being presented. Thanks for your help.
Phil S.
A: Much like wood flooring, the amount of sound reduction garnered from your carpet will be based on the carpet and more importantly, the underlayment you use. Carpet’s big benefit is its impact insolation class (IIC rating). I’ll be honest, I had to spend a bit of time searching for some good info for you, as finding carpet’s STC ratings can be difficult. Basic information I could find was that 40 oz. Carpet with padding would give around a 55 or so on the STC ratings. This however is heavily dependent on what underlayment is used for carpet, and the ratings I found were using basic pad and no special underlayment. What I would like to use is a link to the minimum STC ratings required for public education buildings.
As you can see, beside louder rooms (i.e. A music room) STC ratings of 60 are required. Cork, being a natural insulator, gets great STC and IIC ratings. Most HOAs (Home Owners Association) require the use of cork underlayment when installing a wood floor. The 6mm 5-star cork underlayment we carry has an IIC rating of 50 and an STC rating of 51 in lab tests. This does not include what you get from your floor.
In this case, I would honestly suggest presenting the STC ratings for 6mm cork.
Then compare these ratings to the national standards for public education and it should give your board an idea of how much reduction you can get just from this underlayment, not to mention the cork floor.
End result here, install a good floating cork such as Westhollow or APC, over a 6mm cork underlayment and this should fit the ticket.