IIC Rating for Cork Floor

Q: I have an upstairs condo where I want to replace my carpet with a cork floor. The HOA requires a minimum IIC of 50 for a new floor. The existing floor is has a 5/8 sheet rock ceiling below, 2×12 floor joists, a 3/4 plywood subfloor with 3/4 in gypcrete over that. I plan to put a layer of sound barrier 6, a 1/4 in cork underlayment and your Westhollow cork plank. Will this assembly have a rating of 50 of more? Can you send me your opinion on this that I can send to the HOA?
Regards
Tom McCall
A: Condos have very stringent requirements when it comes to installing wood flooring, but with some careful planning it is very easy to surpass these requirements. With the subfloor assembly you describe and using the particular underlayment and flooring you wish to use you should easily pass the IIC/STC rating of 50 required by your HOA, but let’s dig into a bit of detail on this.
Based on the items you intend to use, I would suggest the following installation set up. Lay down the 1/4″ cork underlayment over your subfloor as a substrate. This will help maintain a bit of the density benefits the cork provides a long with acting as a final line of defense for sound and impact insulation. Now the 5-star rated 6mm cork (just shy of 1/4″) that we carry has a relative IIC rating 55, which means it alone passes the test you have ahead of you. You can expect similar results from other 6mm corks, but let’s drop it down a bit and guess that you will get right on the 50 you are after (most tested scored 53 or 54).
After you have installed the cork, lay the Sound 6 Barrier underlayment over the top. This will act as your initial sound and impact insulation. By having the Sound 6 installed over the cork this prevents the cork underlayment from moving as much (as it would if installed over the sound 6) and maintains a bit less spring in the floor as you walk over it. Sound 6 has an IIC rating of 71, so when you combine that with the 1/4″ cork you should be well over the 50 IIC rating you require. Keep in mind, cork flooring in itself reduces some impact and sound as the top layer of each plank is just over 3mm of cork.
Combined here you should have a 50 IIC at a very minimum and should easily meet your HOA’s needs.