Cork Acoustic IIC 71 Explained: Why It Beats Oak and LVT for Specifier Projects

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Why does cork plank deliver IIC 71-73 when standard solid oak parquet sits around 49-55, and why does the difference matter for a UK commercial specifier? This piece breaks down how Impact Insulation Class is measured, why cork’s closed-cell structure outperforms harder finishes, and how the IIC number translates into BREEAM Hea 02 contribution and post-occupancy noise complaint risk.

What IIC actually measures

Impact Insulation Class (IIC) is the standardised measure of how much footfall and impact noise a floor assembly transmits to the space below. It’s evaluated against ASTM E492 in North America and ISO 717-2 internationally, with a tapping machine generating standardised impact noise on the test floor while a microphone in the room below records sound transmission across one-third octave bands from 100 Hz to 3,150 Hz.

The output is a single integer between roughly 25 (severe transmission) and 80+ (excellent isolation). UK commercial briefs typically demand IIC 50 minimum for office, IIC 55-60 for hotel and residential multi-occupancy, and IIC 65+ for premium WELL-rated workplace.

The numbers, side by side

Cork’s IIC 71-73 sits 15-25 points above standard hard finishes — a substantial gap. The IIC scale is logarithmic, so each 10-point gain represents roughly a halving of perceived transmitted impact noise. In practical terms: footfall on a cork floor reads as a soft tap one storey down; on solid oak parquet at the same flow it reads as a hard click that listeners can locate by ear.

Why cork outperforms the alternatives

Cork’s IIC advantage comes from its cellular structure. Each cubic centimetre of cork contains roughly 40 million closed cells of trapped gas, separated by thin walls of suberin (a waxy polymer). When a foot strikes the floor, the impact energy compresses the cells, which absorb the kinetic energy and dissipate it as low-amplitude internal heat rather than transmitting it through the substrate as acoustic energy.

Solid oak doesn’t have the cellular density. The wood structure transmits impact energy efficiently into the joist or screed substrate, which then radiates the noise into the room below. Adding underlay can recover 5-10 IIC points but introduces install complexity and a softer underfoot read that some brief-writers reject.

LVT performs at solid-oak level despite being softer underfoot because the polymer construction is dense and homogeneous — it transmits impact energy through the layer rather than absorbing it. The acoustic foam backings on premium LVT recover ground but rarely match cork without significant added thickness.

BREEAM Hea 02 and SKA Rating contribution

BREEAM Hea 02 (Acoustic Performance) awards credits based on whether the building’s acoustic performance meets defined targets for indoor ambient noise, sound insulation, indoor reverberation, and external noise. For multi-occupancy interiors, the impact-sound transmission target is typically L’nT,w ≤ 50-55 dB depending on building type — which corresponds approximately to IIC 55-60 in the source assembly.

Cork at IIC 71-73 comfortably exceeds the BREEAM Hea 02 target, contributing to project credit allocation without requiring additional acoustic underlay or floating-floor buildup. On office fit-outs assessed under SKA Rating, cork contributes to acoustic performance criteria under the Materials and Wellbeing categories without needing supplementary detailing.

The practical specifier benefit: cork delivers the acoustic credit in a single material specification, where harder finishes typically need a second-layer acoustic underlay to meet the same target — which adds cost, install time, and floor buildup.

Where the difference lands in real projects

The Waterman, Farringdon Lane. Three London design practices (Ambit Moat, Fathom Architects, Fettle Design) specified Classic Cork Original Shell across all offices, meeting rooms and circulation. Cork’s IIC 71 was central to delivering a calm acoustic profile across the open-plan workplace floor without specifying additional underlay or a floating-floor system.

Sybarite, Sloane Square. The architecture practice runs Original Natural cork across their own materials library and open-plan studio. The IIC 71 means the team can hold meetings, take calls and draft to the soft tap of cork rather than the hard click of solid timber — a real working-day difference.

Klay London apartment. Artform + Scene Smith specified Cork Styles Original Shell for a residential interior with an IIC 73 acoustic brief from the developer. The cork delivered the brief in a single material specification, eliminating the need for a separate impact-isolation layer between the floor and the underlying joist structure.

Specifier read-throughs

For the cork ranges that drove the analysis: Classic Cork Collection (7mm) and Cork Styles Collection (11mm). For the workplace acoustic application: Cork Flooring for Offices. For project-specific BREEAM contribution evidence: Architect Resources Hub. For the London-specific specifier guide: Sustainable Flooring London.

Acoustic figures cited are typical lab-test values per range. Project-specific IIC depends on the substrate assembly — joist construction, screed, ceiling buildup. Confirm against the project-specific acoustic survey + range TDS.