Specifying Oak Flooring for Multi-Storey and Commercial Projects

On a house, flooring is a design decision. On an apartment building, a hotel, a care facility or any inter-tenancy work, it is a consent decision, and the wrong specification surfaces late and expensively.

Two requirements govern almost every multi-storey timber floor in New Zealand: fire performance and acoustic performance. Here is what each one actually asks for.

Fire: Critical Radiant Flux under ISO 9239-1

The Building Code requires floor coverings to be tested under ISO 9239-1 to establish Critical Radiant Flux, which measures how the covering behaves when exposed to heat and flame.

Minimum values vary by space type, from 1.2 kW/m² in standard occupied rooms up to 4.5 kW/m² for the most demanding care and detention facilities.

Independent testing puts Marchand engineered oak at a CRF of 5.0 kW/m². That clears every threshold in the code:

• Above the 1.2 kW/m² threshold for general occupied areas
• Above the 2.2 kW/m² requirement for exitways and unsprinklered commercial firecells with more than 50 occupants
• Above the strictest 4.5 kW/m² benchmark for sleeping areas and exitways in care homes and detention facilities

The full result is published as the Reaction to Fire Test, AS ISO 9239.1.

Fire separation: the 20mm threshold in C/AS2

CRF is only half of it. For fire-separating floors, Acceptable Solution C/AS2 Part 4, paragraph 4.17.5, recognises that timber flooring over a separation floor contributes to fire load, and therefore requires either:

• a flooring layer at least 20mm thick, or
• a full floor assembly tested to achieve an FRR of −/30/30.

This is where thinner boards become a problem. A 12, 14 or 16mm board pushes responsibility back onto the designer to prove the assembly achieves the FRR, which generally means paying for testing or introducing an additional fire-rated build-up. Both cost money and both arrive late in the consent process.

Our boards are 20mm as standard, so the thickness route is satisfied automatically. No assembly testing, no special detailing, no redesign. We cover the broader case for the dimension in why 20mm is the New Zealand standard.

Acoustics: impact sound between tenancies

Footfall noise is the complaint that dominates apartment living, and it is an inter-tenancy compliance issue rather than a comfort preference.

Our acoustic underlay is a 3mm mat made from a blend of chip rubber, tested to ISO 10140-3 for impact sound reduction in a reverberation chamber. The results:

• Weighted impact sound reduction ΔLw = 11 dB, measured on the 20mm flooring laid over the 3mm rubber underlay rather than on the board alone
• Spectrum adaptation terms CI,Δ = 8 dB, CI,r = −3 dB

The full result is published as the Acoustic Underlay Test Report. The mat is supplied in 3mm only, which suits standard installation build-ups, and it conforms to minor substrate irregularity without telegraphing. It is part of the specified system rather than a shelf item. It is not sold through the online store, and it is arranged with us alongside the flooring for the project.

Installing the acoustic underlay

The mat is straightforward but unforgiving of shortcuts. The following is the guidance we give rather than a published specification, so confirm it against the adhesive and underlay data sheets for your project:

• Not compatible with underfloor heating. Where a project has both, the underlay is not the right product and the specification needs revisiting.
• Lay perpendicular to the flooring planks for optimal performance.
• Prepare the substrate so it is smooth, level and free of debris.
• Acclimatise the underlay in the installation area for at least two hours before cutting or adhering.
• Adhesive: the tested build-up used Bona Silane. Confirm the adhesive with us before the build-up is finalised.
• Complete all trimming and gluing in one day so bonding is consistent.
• Roll with a stand-up roller after laying, then again after 30 minutes, to ensure adhesive transfer.
• Cure for 12 to 24 hours before laying the flooring.
• Protect from foot traffic and other trades until the floor goes down.

The flooring build-up above it follows the Installation Instructions.

What this means at consent stage

A 20mm board with a 5.0 kW/m² CRF and a tested acoustic mat removes three of the most common late-stage flooring problems on a multi-storey project: an FRR test nobody budgeted for, a CRF value that limits which spaces the floor can go in, and an acoustic report that comes back short.

The reaction to fire test, the acoustic underlay test report, the technical specifications and the installation instructions all sit in Resources. Completed commercial and multi-unit work is documented under Projects.

For a project in consent now, book a design consultation and we will work through the specification with you.