IIC Rating Calculator
Estimate the Impact Insulation Class (IIC) rating of a floor-ceiling assembly based on floor type, underlayment, finish, and ceiling treatment.
About this calculator
This calculator estimates a floor-ceiling assembly's Impact Insulation Class (IIC) -- the single-number rating for footstep and impact noise transmission, derived from lab testing per ASTM E492 (standard tapping-machine method) or the field equivalent ASTM E1007, and rated against the ASTM E989 reference contour -- using a points system rather than a lab measurement. It starts from a Base IIC that scales with floor thickness (roughly 1.7 IIC points per inch for concrete slab, 1.2 for wood frame, reflecting concrete's greater mass and inherent damping), then adds points for underlayment, floor finish, and ceiling treatment. Floor Thickness is a safe, always- active lever -- thicker structure always raises Base IIC regardless of every other input's setting.
The other three treatments interact, though: underlayment only helps when an underlayment type other than "none" is actually selected, since the points system multiplies each underlayment's base rating by a thickness factor that is zero whenever underlayment type is "none" -- the Underlayment Thickness field itself only appears once an underlayment type is selected. Floor finish is the single largest lever available: carpet with pad adds a full 20 points, dwarfing the 1-3 points from hard finishes like tile, laminate, or engineered wood, which is consistent with why carpet is the most common impact-noise mitigation recommended for multifamily construction. IBC code minimum for multifamily separation is IIC 50, and Points Below Code reports how far short (if at all) the current assembly falls.
Inputs
Results
Estimated IIC rating
32
Figures current as of 2022. Sources: ASTM E492-22, Standard Test Method for Laboratory Measurement of Impact Sound Transmission Through Floor-Ceiling Assemblies Using the Tapping Machine, ASTM E1007-21, Standard Test Method for Field Measurement of Tapping Machine Impact Sound Transmission Through Floor-Ceiling Assemblies and Associated Support Structures, ASTM E989-06(2012), Standard Classification for Determination of Impact Insulation Class (IIC), International Building Code, Chapter 12, "Sound Transmission" provisions (Section 1207 in the 2021 edition)
How to Use This Calculator
- Enter Floor structure type, Slab/subfloor thickness (in), and Underlayment type.
- Set Underlayment thickness (in), Floor finish, and Ceiling below.
- Review the Estimated IIC rating result.
- Use Base IIC (bare structure) and Underlayment improvement (pts) to inform your decision.
How the result changes with Slab/subfloor thickness (in)
| Slab/subfloor thickness (in) | Estimated IIC rating |
|---|---|
| 3 | 27 |
| 4.5 | 30 |
| 9 | 37 |
| 12 | 42 |
What each input means
- Floor structure type
- Concrete provides better base impact isolation.
- Slab/subfloor thickness (in)
- Thickness of concrete slab or wood subfloor in inches.
- Underlayment type
- Material laid under the finish flooring to absorb impact energy.
- Underlayment thickness (in)
- Thickness of the underlayment layer in inches. Common: 1/8", 1/4", 3/8", 1/2".
- Floor finish
- The wearing surface installed over the subfloor.
- Ceiling below
- Ceiling assembly on the underside of the floor above.
What each result means
- Estimated IIC rating
- Estimated Impact Insulation Class rating. IBC code minimum is IIC 50 for multifamily.
- Base IIC (bare structure)
- IIC rating of the bare floor structure without treatments.
- Underlayment improvement (pts)
- IIC points gained from the underlayment layer.
- Floor finish improvement (pts)
- IIC points gained from the floor surface finish.
- Ceiling improvement (pts)
- IIC points gained from the ceiling treatment below.
- Meets IBC code (1=yes, 0=no)
- Whether the assembly meets IBC minimum IIC 50 requirement.
- Points below code
- Number of IIC points needed to reach code minimum (0 if already met).
- Quality rating (0-4)
- 0 = Poor, 1 = Below code, 2 = Meets code, 3 = Good, 4 = Excellent.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersFloor structure type = 1, Slab/subfloor thickness (in) = 6, Underlayment type = 0, Underlayment thickness (in) = 0.25 = 6 input(s) provided
- Calculate Estimated IIC ratingEstimated IIC rating32 = 32
- Calculate Base IICBase IIC32 = 32
- Calculate Underlayment improvement0 = 0
Figures and sources
- Laboratory tapping-machine impact sound transmission test method (2022) — ASTM E492-22, Standard Test Method for Laboratory Measurement of Impact Sound Transmission Through Floor-Ceiling Assemblies Using the Tapping Machine
- Field tapping-machine impact sound transmission test method (2021) — ASTM E1007-21, Standard Test Method for Field Measurement of Tapping Machine Impact Sound Transmission Through Floor-Ceiling Assemblies and Associated Support Structures
- Impact Insulation Class (IIC) reference contour and classification procedure (2012) — ASTM E989-06(2012), Standard Classification for Determination of Impact Insulation Class (IIC)
- IBC minimum IIC 50 (or 45 if field-tested) for floor-ceiling assemblies between dwelling units (2021) — International Building Code, Chapter 12, "Sound Transmission" provisions (Section 1207 in the 2021 edition)
Engine last updated . Checked against 3 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
What single change raises IIC the most?
Adding carpet with pad as the floor finish -- it contributes a full 20 points in this calculator, far more than any single underlayment, ceiling treatment, or realistic floor-thickness increase. Hard finishes like tile, laminate, or engineered wood only add 1-3 points by comparison, which is why carpet remains the most common impact-noise fix in multifamily buildings.
Why isn't there an underlayment thickness field to fill in?
Underlayment Thickness only appears once you select an underlayment type other than "None." The underlayment bonus is that underlayment's base rating (8 for cork, 12 for rubber, 10 for foam, 14 for fiber) multiplied by a thickness factor -- with no underlayment type selected, that base rating would be zero regardless of thickness, so the field stays hidden until it can actually change the result. Select an actual underlayment material first, and the thickness field will appear.
Does floor thickness always help, no matter what else I choose?
Yes. Floor Thickness feeds Base IIC directly and unconditionally -- it adds roughly 1.7 IIC points per inch for a concrete slab or 1.2 points per inch for a wood frame floor, regardless of what underlayment, finish, or ceiling treatment is selected. It is the one input in this calculator with no dependency on any other setting.
Is this the same IIC I'd get from a lab or field test?
No. This calculator applies a published rule-of-thumb points system; a certified rating comes from tapping-machine testing per ASTM E492 in a lab or ASTM E1007 in the field, scored against the ASTM E989 reference contour. Use this estimate for early design comparisons, not as a substitute for a lab-tested or manufacturer-published assembly rating.
Why does rubber underlayment score higher than cork?
In this calculator's points system, rubber underlayment contributes 12 IIC points at full thickness versus 8 for cork -- rubber's higher density and damping characteristics make it more effective at absorbing impact energy before it transmits through the floor structure. Recycled fiber underlayment scores highest of the four options at 14 points.
Related Calculators
The questions that sit next to this one — chosen by subject, including calculators filed under a different category.
STC Rating Calculator
Estimate Sound Transmission Class (STC) for wall assemblies based on wall type, drywall layers, insulation, stud spacing, resilient channel, and staggered studs.
AcousticsNoise Reduction Coefficient Calculator
Analyze sound flanking transmission paths. Input the STC of the direct path and each flanking path (walls, floor, ceiling) to find the apparent STC and weakest link.
AcousticsHVAC Noise Calculator
Estimate HVAC duct noise levels in a room from fan data, duct geometry, and fittings. Calculates sound power, duct attenuation, breakout noise, and NC rating.
Fire SafetyFire Resistance Rating Calculator
Calculate fire resistance rating from material type and thickness, compare to IBC requirements.
More in Construction & Building Trades.