Sound Advice

IIC Rating Chart: How Quiet Is the Floor Above?

Posted on by Austin Peek
IIC Rating Chart - How Quiet is the Floor Above
01
Nov

What Is an IIC Rating?

An Impact Insulation Class (IIC) rating measures how well a floor-ceiling assembly blocks impact noise — footsteps, dropped objects, dragged chairs, dog claws — from passing into the space below. While STC ratings measure airborne sound transmission, IIC measures structure-borne impact. They are independent: a wall or floor can pass STC and fail IIC, or vice versa.

The IIC scale typically runs from about 20 (bare concrete with no finish) to 80 (fully decoupled assemblies in recording studios). The International Building Code requires a minimum of IIC 50 (laboratory) or IIC 45 (field) between dwelling units. Most professional specifications aim higher than code to absorb the typical 2–5 point lab-to-field penalty.

IIC Rating Chart – Typical Floor-Ceiling Assemblies

IIC 25–35
Low Performance
Footsteps clearly audible; not code-compliant
IIC 36–49
Moderate
Below IBC dwelling-unit minimum
IIC 50–59
Code-Compliant
IBC multifamily minimum; standard target
IIC 60–80
High Performance
Studios, theaters, premium hospitality
TypeAssemblyConstructionIICVisual RangeImpact Performance
CONCRETEBare 6″ concrete slabNo finish or ceiling treatment25–30
Footsteps clearly audible
CONCRETE6″ concrete + vinyl tileHard finish over slab28–32
Footsteps & dropped objects loud
CONCRETE6″ concrete + carpet & padStandard cushion carpet50–65
Code-compliant with most carpet systems
CONCRETE6″ concrete + acoustic underlayment + tileRubber/cork mat under hard surface55–65
Common multifamily detail
CONCRETECLT + topping slab + underlaymentMass-timber multifamily50–60
Emerging construction type
WOODWood joist + ½″ subfloor + carpet onlyNo ceiling treatment30–40
Below code; lightweight baseline
WOODWood joist + GWB ceiling + carpet & padStandard residential build42–50
At or near IBC minimum
WOODWood joist + RC + 5/8″ GWB + carpet & padResilient channel ceiling50–58
Reliable code path for wood multifamily
WOODWood joist + clip-isolated ceiling + LVTDecoupled clips + acoustic underlayment55–65
High-end multifamily; tile/LVT finish
FLOATING6″ concrete + floating floor systemSpring or rubber-decoupled topping slab65–75
Hotel guestroom-grade isolation
FLOATINGConcrete + floating floor + isolated ceilingDouble-decoupled assembly70–80
Studios, theaters, premium hospitality

Required IIC Ratings by Building Type

Code requirements set the floor — most professional specifications aim higher than the minimum. Use this table to translate building type into a target IIC.

SectorBuilding TypeCode MinRecommended IICSource / Notes
RESIDENTIALMultifamily / ApartmentsIIC 50
IIC 55–60
IBC §1206 between dwelling units
HOSPITALITYHotels & HospitalityIIC 50
IIC 55–65
Marriott/Hilton brand specs often higher
RESIDENTIALCondominiums (premium)IIC 50
IIC 60–65
HOA / brand standards above code
HEALTHCAREHospitals & HealthcareIIC 48
IIC 55–65
FGI Guidelines; patient room privacy
EDUCATIONSchools (above classrooms)IIC 45
IIC 50–55
ANSI S12.60 between learning spaces
COMMERCIALAbove-commercial dwellingsnone
IIC 60–65
Restaurants/retail below; impact critical
PERFORMANCERecording studiosnone
IIC 70–80
Floating floor / decoupled ceiling required
PERFORMANCETheaters / Performancenone
IIC 65–75
Catwalks, mezzanines, equipment lofts
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Key Takeaway
For most commercial and multifamily work, target IIC 55–60, not the IBC minimum of 50. The 5-point cushion absorbs the typical 2–5 point Field IIC penalty from real-world workmanship and flanking paths — keeping the finished floor code-compliant on testing day. Concrete-and-carpet assemblies typically meet code without extra effort; wood-framed assemblies almost always need a resilient channel ceiling and acoustic underlayment.

Choosing the Right IIC Rating

  • IIC 25–35: Bare slab or hard-surface concrete; footsteps clearly audible below.
  • IIC 36–49: Standard residential wood framing with carpet; below IBC dwelling-unit code.
  • IIC 50–59: Code minimum for multi-family; resilient channel ceilings and acoustic underlayment in wood-framed work.
  • IIC 60+: High performance; recommended for above-commercial dwellings, hotels, studios, and theaters.

Three factors determine which IIC target is right for your project:

  • Structural system: Concrete plates start ~10 IIC points ahead of wood joists. If you’re framing in wood, plan for resilient channel ceilings and acoustic underlayment.
  • Finish flooring: Hard finishes (LVT, tile, hardwood) drop IIC by 10–25 points unless paired with acoustic underlayment. Carpet with pad is the easiest path to code.
  • Field IIC penalty: Plan for a 2–5 point drop from lab to field due to flanking through walls, soft joints, and ceiling penetrations.

Sizing an assembly? Use our IIC Calculator to estimate the rating of a planned floor-ceiling system, or pair it with the STC Calculator to verify airborne and impact performance together. Both tools account for the typical Field IIC penalty.

Field vs. Laboratory Ratings

  • Lab IIC: Measured under controlled conditions per ASTM E492 using a tapping machine.
  • Field IIC (FIIC or AIIC): Real-world measurement per ASTM E1007 in an installed building.

Field IIC ratings often test 2–5 points lower than laboratory results due to flanking paths through walls and connecting structure, plus workmanship variations in underlayment seams, perimeter isolation, and ceiling penetrations. Spec the assembly to land 5 points above your code target to absorb the penalty.

Conclusion: Designing for Impact Noise Control

The IIC rating chart provides a working reference for predicting how floor-ceiling assemblies perform against impact noise. Pair it with the STC rating chart when specifying assemblies — both ratings need to pass for a building to feel quiet. Concrete-and-carpet wins by default; wood-framed projects need resilient channel ceilings and acoustic underlayment to clear IIC 50. The 5-point cushion above code is what keeps the finished building out of trouble on testing day.

FAQs: IIC Rating Chart

What IIC rating is required by code?

The International Building Code requires a minimum of IIC 50 (laboratory) or IIC 45 (field) between dwelling units. Higher ratings are often specified for hotels, hospitals, and premium condominiums to absorb the typical 2-5 point lab-to-field penalty.

What is the difference between IIC and STC?

IIC measures impact noise (footsteps, dropped objects) transmitted through floor-ceiling assemblies. STC measures airborne sound (voices, music) transmitted through walls or floors. Both need to pass for an assembly to feel quiet — they are independent ratings.

What IIC rating is good for an apartment?

IIC 50 is the IBC code minimum, but most professional specifications aim for IIC 55-60 to absorb the field-test penalty and produce a quiet apartment in real-world conditions.

Can a wood-framed floor reach IIC 60?

Yes, but it requires careful detailing: resilient channel ceilings, acoustic underlayment, perimeter isolation strips, and sealing of all penetrations. Concrete-and-carpet assemblies reach IIC 60 more easily.

What is FIIC?

FIIC (Field IIC) is the IIC rating measured in an installed assembly using ASTM E1007. It typically tests 2-5 points lower than the laboratory IIC due to flanking paths and workmanship.

Austin Peek