Achieve Excellent Acoustic and Fire Performance with Dimond's Composite Steel Flooring Systems

Designing medium-density intertenancy floors requires careful consideration across a number of priorities including balancing structural depth, acoustic isolation, and fire compliance without compromising construction speed and cost. Dimond Structural composite flooring range solves this by using roll-formed galvanised steel profiles as permanent formwork, eliminating the slow curing timelines of traditional precast concrete.

For designers, the challenge is not only meeting performance requirements under the New Zealand Building Code (NZBC), but doing so in a way that is practical for design, detailing, and construction.

For flexibility, designers can select from three distinct Dimond profiles:

Dimond Flatdeck: Delivers a clean, flat-soffit aesthetic that can be left exposed for a modern, industrial interior look.
Dimond Hibond 55: Offers a classic, highly efficient trapezoidal profile optimised for standard residential footprints.
Dimond Hibond 80: Features a deep cross-section (150mm to 230mm slabs) engineered for exceptionally long, unpropped spans. This clears the lower floor area for immediate trade access and reduces construction and cost.

Acoustic compliance under NZBC Clause G6 is built into these systems

Acoustic separation remains a critical consideration for intertenancy floors under NZBC Clause G6. Dimond Structural flooring systems are supported by testing from the University of Auckland and analysis by Marshall Day Acoustics, providing validated performance data.

Representative results include:

140mm Flatdeck slab: 52dB STC (bare)
140mm Hibond 55 slab: 44dB STC (bare)
150mm Hibond 80 slab: 47dB STC (bare)

When combined with a suspended ceiling and 75mm cavity absorber, performance increases to:

67dB STC (Flatdeck)
61dB STC (Hibond 55)
68dB STC (Hibond 80)

These configurations exceed typical intertenancy requirements, with acoustic performance improving further as slab thickness increases — reaching up to 57dB STC bare for a 200mm Flatdeck.

As with all acoustic systems, detailing remains critical. Service penetrations such as lighting and mechanical systems must be carefully considered to avoid compromising overall performance.

Fire resistance and compliance pathways

Fire design for intertenancy floors is addressed in accordance with NZBC Clauses C3 and C4, supported by HERA slab panel methods (R4-82 and R4-131).

Hibond 80 achieves a 60-minute Fire Resistance Rating (FRR) as a base condition (tested to EN 1365-2), with the ability to extend to 120 minutes through additional reinforcement.
Hibond 55 can achieve a 30-minute FRR for spans under 4.0 metres without reinforcement.

These established design pathways support efficient compliance documentation and coordination across disciplines.

Serviceability and in-use performance

In addition to strength and compliance, serviceability is a key consideration for occupant comfort. Dimond Structural flooring systems are designed with vibration control in mind, with span tables targeting a natural frequency limit of 5.0Hz for foot traffic.

Project-specific engineering assessment remains important to evaluate the behaviour of the full structural system, including primary supports.

Supporting intertenancy design in practice

Intertenancy floor systems must ultimately deliver consistent, real-world performance — not just in isolation, but as part of a coordinated building solution.

Dimond Structural’s composite flooring systems bring together structural efficiency, acoustic separation, and fire compliance within a system that is practical to document and construct. By offering flexibility in profile selection alongside validated performance data, the system supports clearer design decisions and better outcomes on site.

For specifiers working across increasingly complex residential and mixed-use developments, this alignment between design intent and buildability is an important part of delivering compliant, durable, and comfortable intertenancy environments.

Hibond 80 Composite Steel Flooring System

Dimond Structural

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Hibond 80 is a composite steel flooring system with the deepest flooring profile allowing longer un-propped spans, minimising beam layout.

NZ Made

NZ-Owned Business

Dimond Structural Flooring Systems use a roll-formed profiled galvanised steel sheet as a component in reinforced concrete floor systems
The steel decking sheet provides both permanent formwork and positive tensile reinforcement in one way reinforced composite floor slab construction over concrete block walls, poured concrete beams, steel beams or timber beams, subject to the environmental limitations referenced to the appropriate grade of the material selected
It is critical to product performance that the loads applied, spans, formwork material thickness and overall composite floor slab thickness are designed within the appropriate Limit State Loads and limitations published in Flooring Systems Design Manual
Before commencing a project using a Dimond Structural Flooring System, the user must refer to the information within the manual and all sections as appropriate, ensuring relevant information is available to the end-user. Failure to observe this information may result in a significant reduction in product performance
Dimond Structural accepts no liability whatsoever for products which are used otherwise than in accordance with these recommendations.

Past history of use of Dimond Structural Flooring Systems indicate that provided the system design, product use and maintenance is in line with the guidelines of Flooring Systems Design Manual, Dimond Structural Flooring Systems can reasonably be expected to meet the performance criteria in Clause B1 Structure and B2 Durability of the New Zealand Building Code for a period of not less than 50 years, provided they are kept free from moisture.

Dimond Structural Flooring Systems designed using the Fire Design Sections 3.3.4, 3.4.6 and 3.5.6 of this manual and will meet the performance criteria in Clauses C3 and C4 of the New Zealand Building Code (section 3.3.4 is based on testing to EN 1365-2 and sections 3.4.6 and 3.5.6 are based on HERA reports R4-82 and R4-131).

Using the Flooring Acoustic Performance sections 3.3.5, 3.4.7 and 3.5.7, Dimond Structural Flooring Systems can be designed using this manual for guidance to achieve Sound Transmission Class (STC) and Impact Insulation Class (IIC) of 55 meet the requirements of the current New Zealand Building Code Clause G6, airborne and impact sound.

Where products used in Dimond Structural Flooring Systems are manufactured by other suppliers, compliance to the New Zealand Building Code should be checked with that product's manufacturer.

Hibond 55 Composite Steel Flooring System

Dimond Structural

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Hibond 55 is a composite steel flooring system that has been successfully used in a wide variety of commercial and residential applications for over thirty years.

NZ Made

NZ-Owned Business

Dimond Structural Flooring Systems use a roll-formed profiled galvanised steel sheet as a component in reinforced concrete floor systems
The steel decking sheet provides both permanent formwork and positive tensile reinforcement in one way reinforced composite floor slab construction over concrete block walls, poured concrete beams, steel beams or timber beams, subject to the environmental limitations referenced to the appropriate grade of the material selected
It is critical to product performance that the loads applied, spans, formwork material thickness and overall composite floor slab thickness are designed within the appropriate Limit State Loads and limitations published in the Flooring Systems Design Manual
Before commencing a project using a Dimond Structural Flooring System, the user must refer to the information within this manual and all sections as appropriate, ensuring relevant information is available to the end-user. Failure to observe this information may result in a significant reduction in product performance
Dimond Structural accepts no liability whatsoever for products which are used otherwise than in accordance with these recommendations

Past history of use of Dimond Flooring Systems indicate that provided the product use and maintenance is in line with the guidelines of the Flooring Systems Design Manual Dimond Flooring Systems can reasonably be expected to meet the performance criteria in Clause B1 Structure and B2 Durability of the New Zealand Building Code (NZBC) for a period of not less than 50 years, provided they are kept free from moisture.

Dimond Flatdeck Composite Steel Flooring System

Dimond Structural

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Flatdeck is a versatile, lightweight composite steel flooring system that makes full use of the combined structural properties of both steel and concrete.

NZ Made

NZ-Owned Business

Dimond Structural Flooring Systems use a roll-formed profiled galvanised steel sheet as a component in reinforced concrete floor systems
The steel decking sheet provides both permanent formwork and positive tensile reinforcement in one way reinforced composite floor slab construction over concrete block walls, poured concrete beams, steel beams or timber beams, subject to the environmental limitations referenced to the appropriate grade of the material selected
It is critical to product performance that the loads applied, spans, formwork material thickness and overall composite floor slab thickness are designed within the appropriate Limit State Loads and limitations published in the Flooring Systems Design Manual
Before commencing a project using a Dimond Structural Flooring System, the user must refer to the information within the manual and all sections as appropriate, ensuring relevant information is available to the end-user. Failure to observe this information may result in a significant reduction in product performance
Dimond Structural accepts no liability whatsoever for products which are used otherwise than in accordance with these recommendations

Past history of use of Dimond Structural Flooring Systems indicate that provided the system design, product use and maintenance is in line with the guidelines of the Flooring Systems Design Manual, Dimond Structural Flooring Systems can reasonably be expected to meet the performance criteria in Clause B1 Structure and B2 Durability of the New Zealand Building Code for a period of not less than 50 years, provided they are kept free from moisture.

Dimond Structural Flooring Systems designed using the Fire Design Sections 3.3.4, 3.4.6 and 3.5.6 of the manual and will meet the performance criteria in Clauses C3 and C4 of the New Zealand Building Code (section 3.3.4 is based on testing to EN 1365-2 and sections 3.4.6 and 3.5.6 are based on HERA reports R4-82 and R4-131).

Using the Flooring Acoustic Performance sections 3.3.5, 3.4.7 and 3.5.7, Dimond Structural Flooring Systems can be designed using the manual for guidance to achieve Sound Transmission Class (STC) and Impact Insulation Class (IIC) of 55 meet the requirements of the current New Zealand Building Code Clause G6, airborne and impact sound.

Where products used in Dimond Structural Flooring Systems are manufactured by other suppliers, compliance to the New Zealand Building Code should be checked with that product’s manufacturer.

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