Delta IIC is a rating that quantifies the improvement in impact sound isolation achieved by adding an underlayment to a floor-ceiling assembly. It represents the change in the Impact Insulation Class (IIC) rating resulting solely from the underlayment's presence.
Understanding Delta IIC
The Impact Insulation Class (IIC) measures a floor-ceiling assembly's ability to block impact sounds, such as footsteps or dropped objects. A higher IIC rating indicates better sound isolation. However, the IIC of a floor depends on the entire assembly, including the subfloor, flooring material, and any underlayment.
Delta IIC focuses specifically on the added value of the underlayment. It answers the question: "How much better does the floor perform in terms of impact sound isolation because of this underlayment?"
Calculating Delta IIC
Delta IIC is calculated as the difference between two IIC measurements:
- IIC with Underlayment: The IIC rating of the complete floor-ceiling assembly including the underlayment.
- IIC without Underlayment: The IIC rating of the floor-ceiling assembly without the underlayment.
The formula is:
Delta IIC = IIC (with underlayment) - IIC (without underlayment)
For example, if a floor assembly has an IIC of 40 without an underlayment and an IIC of 60 with an underlayment, the Delta IIC is 20.
Importance of Delta IIC
Delta IIC is useful for several reasons:
- Underlayment Performance: It allows you to directly compare the sound isolation performance of different underlayments independent of the rest of the floor assembly.
- Code Compliance: Building codes often specify minimum IIC ratings for floor-ceiling assemblies. Delta IIC can help determine if an underlayment will provide sufficient improvement to meet those requirements.
- Noise Reduction: Delta IIC allows builders to estimate the sound reduction a specific underlayment will provide to tenants in apartments.
Example Scenario
Consider a multi-family dwelling where the building code requires a minimum IIC rating of 50. The existing floor assembly (without underlayment) has an IIC of 40. To comply with the code, the builder needs to increase the IIC by at least 10 points. By selecting an underlayment with a Delta IIC of 10 or higher, the builder can meet the code requirements and reduce noise transmission.
In Summary
Delta IIC is a valuable metric for assessing the sound isolation contribution of underlayments, enabling informed decisions for code compliance and noise reduction in building construction.
