IIC Calculator: Impact Sound Rating Tool for Floors!

The Basics

What is Impact Insulation Class (IIC)?

Impact Insulation Class (IIC) is a standardized single-number rating that quantifies how well a floor-ceiling system attenuates structure-borne impact noise — footsteps, dropped objects, or rolling carts. It is calculated from frequency data collected under ASTM E492, then rated using ASTM E989. Higher IIC values mean better impact isolation and quieter spaces for occupants below.

What It MeasuresHow well a floor assembly reduces impact noise reaching the room below.

The StandardsASTM E492 for the lab impact test, ASTM E989 for the rating procedure.

Where It’s UsedFlooring specs for multi-story residential and commercial buildings.

Benchmarks

Typical IIC Ratings by Assembly Type

Floor assemblies vary widely in performance. Carpet over slab delivers high IIC values, while vinyl or tile over a bare slab performs poorly. For hard-surface floors, an acoustic underlayment and a suspended ceiling below boost performance dramatically — especially in wood-framed buildings where vibration travels further.

Concrete Slab + CarpetExcellent performance

65–75

Wood Joist + Underlayment + DrywallModerate performance

50–60

Concrete + Acoustic Mat + Hard SurfaceImproved performance

50–60

Concrete Slab + LVTNo underlayment — poor isolation

25–35

2035506580

By the Numbers

Impact Performance by Flooring Type & Ceiling Assembly

Small changes in underlayment thickness or ceiling design make big differences. A 10mm underlayment under hardwood on a resiliently-mounted ceiling reaches IIC 57–60, compared to the low 30s with no underlayment and an exposed ceiling. See how IIC, STC, and Delta IIC relate.

Below 5050–54 meets code55+ premiumWithout cavity insulation — fiberglass batts add 2 points.

		Wood Joist					Concrete
Ceiling	Underlayment	LVT	Carpet	Tile	Laminate	Hardwood	LVT	Carpet	Tile	Laminate	Hardwood
Exposed Ceiling	None	33	47	30	32	32	36	50	33	35	35
	2mm	37	51	34	36	36	40	54	37	39	39
	3mm	38	52	35	37	37	41	55	38	40	40
	5mm	45	59	42	44	44	48	62	45	47	47
	10mm	48	62	45	47	47	51	65	48	50	50
Hard-Mounted Drywall	None	35	49	32	34	34	38	52	35	37	37
	2mm	39	53	36	38	38	42	56	39	41	41
	3mm	40	54	37	39	39	43	57	40	42	42
	5mm	47	61	44	46	46	50	64	47	49	49
	10mm	50	64	47	49	49	53	67	50	52	52
Resiliently-Mounted Drywall	None	43	57	40	42	42	46	60	43	45	45
	2mm	47	61	44	46	46	50	64	47	49	49
	3mm	48	62	45	47	47	51	65	48	50	50
	5mm	55	69	52	54	54	58	72	55	57	57
	10mm	58	72	55	57	57	61	75	58	60	60

Design Targets

IIC Requirements by Building Type

The International Building Code requires a minimum lab-tested IIC of 50 (or 45 field-tested) between dwelling units in multifamily buildings. Many design teams aim higher — especially in high-end developments, hospitality, and healthcare — and some brands set their own internal standards.

Code Minimum

IIC 50

Multifamily Dwellings

45 field-tested

Education

IIC 50+

Schools & University Dorms

Footfall control in dorms

Hospitality

IIC 55–60

Hotels & Guest Rooms

Guest comfort & reviews

Healthcare

IIC 55+

Senior Living & Healthcare

Sensitive, quiet-first use

Commercial

IIC Varies

Offices & Commercial

Set by noise expectations

Structure

Concrete Floor Systems: STC & Impact Sound Ratings

A bare slab blocks airborne sound well but does little for impact noise. An 8″ solid slab can rate below IIC 35 without an acoustic mat or suspended ceiling, and ribbed or hollow-core slabs often perform worse — so resilient detailing matters most when hard flooring goes over concrete.

Best bare slab: IIC 34. Every untreated slab here lands at least 16 points under the IIC 50 code minimum, even though its STC is already near or above 50.

Concrete Slab

Solid cast-in-place

4″STC

47IIC

20

6″STC

53IIC

27

8″STC

58IIC

34

10″STC

59IIC

31

Composite (Ribbed) Slab

Concrete on metal deck

4″Not a standard thickness

6″STC

51IIC

21

8″Not a standard thickness

10″Not a standard thickness

Hollow Core

Precast plank with voids

4″Not a standard thickness

6″STC

48IIC

23

8″STC

50IIC

28

10″Not a standard thickness

STC — airborne soundIIC — impact sound (bare slab, no finish or ceiling)IIC 50 code minimum

Methodology

How IIC Ratings Are Calculated

IIC testing uses a standard tapping machine that delivers consistent impacts to the test floor. Microphones in the room below capture the noise across a standardized frequency range, and the results are compared to a reference contour to set the final score.

1

Tapping MachineASTM E492 uses a standard tapping machine to simulate footsteps on the floor.

2

Frequency AnalysisSound in the room below is measured from 100–3150 Hz, where structure-borne noise lives.

3

Contour RatingASTM E989 fits the test curve to a reference contour to produce the IIC number.

Improve Performance

Design Tips to Improve Performance

Improving IIC starts with interrupting vibration transfer — adding mass, decoupling layers, or inserting absorptive materials.

1

Use a Resilient UnderlaymentRubber, cork, or MLV under the finish floor adds 10–20 IIC points.

2

Add a Suspended Ceiling BelowEspecially with insulation in the cavity — a major gain on its own.

3

Choose Softer Finish FloorsCarpet outperforms LVT, which outperforms tile, for impact noise.

4

Isolate Hard ConnectionsPerimeter isolation strips and floating assemblies stop flanking paths.

Proof

Case Studies: IIC Rating in Action

Floor underlayment projects across multifamily, mixed-use, education, and custom homes — with the field-tested numbers to back them up.

Art District Flats: Multi-Family Floor Soundproofing

IIC 56–58

Art District Flats — Denver, CO

63,000 SF of Floor Blokker underlayment met strict IIC targets without heavy rubber mats, reaching IIC 56–58 on 5.5″ slabs while streamlining installation for the GC.

Read the case study →

IIC 60

Historic School Renovation — New Orleans

The former McDonogh 19 Elementary became a Civil Rights museum and senior apartments. 18,000 SF of AcoustiStep under new LVT reached IIC 60 while preserving the building’s historic character.

Read the case study →

Multi-Family Floor Soundproofing in Austin, TX - Berkshire Santal

AIIC 52

Berkshire Santal — Austin, TX

75,000 SF of Floor Blokker under hickory hardwood on open-web truss floors — the worst-case assembly — field-tested at ASTC 58 / AIIC 52, beating code by 13 ASTC points.

Read the case study →

Retrofit

Armature Works — Tampa, FL

Food-hall and kitchen noise was bleeding into the second-floor event space. A Floor Blokker retrofit under new hardwood cut airborne and impact noise without ground-up reconstruction.

Read the case study →

LVT Soundproofing Underlayment Floating vs Glue-Down Installation

Floating LVT

LVT Underlayment — Wisconsin

A new multi-family build ran Floor Blokker under floating LVT — the highest-performing install method, lab-validated over both wood-frame and concrete subfloors.

Read the case study →

Second Floor Soundproofing IIC 45 Floor System for Custom Home Construction

IIC 30s → 45

Custom Home — Tampa, FL

Floor Blokker in the second-story subfloor, installed during framing, lifted IIC from the low 30s to about 45 over the master suite below.

Read the case study →

Questions

FAQs: Using the IIC Calculator Effectively

For multifamily buildings, an IIC of 50 (lab) or 45 (field) is required by code. For high-performance or luxury applications, aim for 55–65.

Our calculator estimates based on typical floor assemblies and material combinations. It’s excellent for early design phases or value engineering. For final specs, use lab-tested assemblies or consult an acoustic engineer.

Yes. Acoustic underlayments — like rubber, MLV, cork, or fiber-based mats — can improve IIC by 10–20 points depending on materials used.

Field tests (ASTM E1007) measure real-world performance. Expect results to be 5–10 points lower than lab (ASTM E492) due to installation variables and flanking paths.

No. STC measures airborne sound (like speech); IIC measures impact sound (like footfall). You need both for complete acoustic performance in multi-story buildings.