Guides
Cork underlayment sound ratings: IIC and FIIC numbers for condo board review
Cork underlayment sound ratings: typical IIC and FIIC numbers for cork, foam, rubber and vinyl products, with ASTM E492 and E2179 references, plus condo board notes.
What to take away
- US condo boards commonly accept IIC 50; some upper-floor rules require IIC 55.
- Cork underlayment assemblies usually publish IIC 50 to 53 from ASTM E492, with ASTM E2179 field results of FIIC 48 to 51.
- Foam products often test at IIC 48 to 50, rubber composites at 52 to 56, mass-loaded vinyl at 52 to 57.
- Field numbers run 2 to 4 points below lab numbers, so choose margin.
- Get written board acceptance before you order material.
What is being compared
A board's rule is a number describing a floor assembly, not the underlayment alone. Cork, foam, rubber composite and mass-loaded vinyl are the materials that change that number. US rules use IIC, the Impact Insulation Class from a laboratory test under ASTM E492. Canada uses apparent ratings and National Research Council guidance, which can confuse a US reviewer.
Cork sits in a family of underlayment types that trade height, cost and impact performance. The same cork sheet can pass in one building and fail in the next. If your documents cite IIC, supply IIC evidence.
Named ASTM reports and specific IIC/FIIC numbers
Specific products and their public reports give the board numbers to file. Amorim Acousticork V6 is a 6 mm cork sheet underlayment. Supplier documents for a 6-inch concrete slab with 3/4-inch engineered wood often show IIC 51 under ASTM E492 and FIIC 49 under ASTM E2179. WECU CorkSilent 4.5 mm lists similar IIC 50 to 52 in concrete assemblies.
Underlayment IIC and cost
Cork sheet
- IIC
- 50-52
- Height
- 3-6 mm
- Cost
- $1.20-3.00
Foam
- IIC
- 48-50
- Height
- 2-3 mm
- Cost
- $0.30-0.60
Cork rubber
- IIC
- 52-56
- Height
- 3-5 mm
- Cost
- $2.00-4.00
MLV
- IIC
- 52-57
- Height
- 1-2 mm
- Cost
- $1.00-2.50
QuietWalk by MP Global is a polyethylene foam underlayment. Its typical report shows IIC 48 to 50 over 6-inch concrete with LVT. Regupol Sonus 3 mm cork rubber composite lists IIC 52 to 56, depending on the slab.
AcoustiBlock MLV, a mass loaded vinyl, publishes IIC 52 to 57 with a resilient ceiling. GenieClip RST is a resilient clip system, not an underlayment; post install field tests often report FIIC 60 or higher.
| Product | Typical published IIC (ASTM E492) | Typical published FIIC (ASTM E2179) | Height added | Cost band |
|---|---|---|---|---|
| Amorim Acousticork V6, 6 mm | 51 in concrete slab assembly | 49 in field reports | 6 mm | $1.50 to $3.00 per sq ft |
| WECU CorkSilent 4.5 mm | 50 to 52 | 48 to 50 | 4.5 mm | $1.20 to $2.50 per sq ft |
| QuietWalk foam | 48 to 50 | Rare | 2 to 3 mm | $0.30 to $0.60 per sq ft |
| Regupol Sonus cork rubber | 52 to 56 | Some | 3 to 5 mm | $2.00 to $4.00 per sq ft |
| AcoustiBlock MLV | 52 to 57 | Common | 1 to 2 mm | $1.00 to $2.50 per sq ft |
The ASTM reports for these products name the lab, date, and assembly. Ask for the full PDF before ordering.
The criteria that matter
Five things decide whether a board accepts your paperwork: the standard named, the assembly tested, the height you can add, the binder chemistry, and the field data history.
Documents to request before you buy:
- A lab report that names the full assembly, not the underlayment alone
- The test standard, test date and laboratory
- The impact rating for the assembly as built
- Any field test from a comparable building
- A written statement on compression and indentation
An eco friendly flooring checklist covers material choice, but a board reads numbers rather than claims once you file.
Option by option
- Cork sheet at 3 to 6 mm, such as Amorim Acousticork V6 or WECU CorkSilent, suits glue-down and floating engineered wood over concrete. It adds 3 to 6 mm height and carries a natural material story. IIC 50 to 52 common.
- Cork and rubber composite, such as Regupol Sonus, resists point loads better and suits converted buildings with wood subfloors. It adds 3 to 5 mm and can test IIC 52 to 56.
- Polyethylene foam, such as QuietWalk, is cheap and thin, often 2 to 3 mm. Its reports are generic, usually IIC 48 to 50.
- Mass-loaded vinyl, such as AcoustiBlock MLV, stays under 2 mm and performs well at 1 lb per sq ft. It costs $1.00 to $2.50 per sq ft.
- Resilient clips with a dropped ceiling, such as GenieClip RST, are not an underlayment. Their assembly reliably produces a measured field result of FIIC 60 or higher.
Several of these products now come from recycled interior surfaces, which changes the health story without changing the acoustics.
Where each one wins
Cork is right when the board accepts a documented lab assembly, the subfloor is concrete, and the buyer wants a natural material underfoot. Regupol Sonus wins where chairs and furniture legs are the daily load, or where the subfloor is wood. QuietWalk wins when cost is the binding constraint and the unit sits above a garage or corridor.
AcoustiBlock MLV is right when existing doors and thresholds fix total height. GenieClip RST is the only defensible choice when the board wants a field measurement after installation, or when the neighbour below has already complained. The same discipline that helps you vet a natural insulation contractor applies to the crew that builds your floor.
What none of them solve
No underlayment fixes flanking paths. Sound travels through walls, ductwork and the slab edge, and a board that has heard three complaints will test rather than read.
An underlayment can lift a floor assembly's impact rating. It cannot stop impact energy that never entered the floor.
None of them replace a ceiling assembly in a wood-frame building either. That gap is where most disputes end up.
