The International Code Council says the “minimum” level of performance is IIC-STC 50 in floor-ceiling assemblies and the “preferred” level of performance is IIC-STC 60. So what is IIC and STC, and what do these numbers mean? The Impact Insulation Class is a test that measures the ability to block impact sound of impact noises such as footfalls or objects dropped on a floor. The Sound Transmission Class evaluates the ability of a specific construction assembly to reduce airborne sounds such as voices, stereos, and TV.
With an IIC-STC 50 rating you can expect loud speech not to be audible and impact-vibration noise significantly reduced. An IIC-STC 60 rating represents superior sound proofing that produces minimal complaints of airborne sounds and you may still hear low frequency nuisance noise.
It is important to note that IIC and STC scores are not dependent on any one single element, but a combination of the floor finish, underlayment, subfloor system (concrete slab, wood joist, truss, etc.) insulation in the ceiling cavity, and ceiling details.
When recommending products to achieve the necessary score, it is important to know the baseline numbers you are starting with. A 6-inch concrete slab will have an average baseline sound insulation rating of IIC 28 and STC 30. A typical 8-inch concrete slab has a baseline rating of IIC 32. In order to achieve your targeted sound rating of the floor assembly with the floor coverings attached you will need to add a soundproofing product.
Macon Hardwood recommends several products that add the soundproofing necessary to reach your targets. A 6-mm thick acoustic cork underlay adds sound control benefits to a floor system of IIC-STC 22, and 12-mm thick acoustic cork underlay adds IIC-STC 26. Capital WA200 is another adhesive product suitable for engineered floors that adds an IIC-STC rating of 22.
While we can’t guarantee that you will never hear your neighbor’s high heels and stereo, with a complete floor-ceiling assembly and the right sound-controlling underlayment we bet you’ll be more likely to live in peace with your neighbor.