James Hardie RAB Board

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Smart façade design is key when it comes to protecting a building from the elements. Finding a balance between water and condensation management, air-tightness and non-combustibility can be challenging – particularly when it comes to designing taller and more complex façades. This is why a solution that offers protection and peace of mind is the only way to overcome poor building performance and reduced comfort levels for occupants.

What is RAB Board?

Introducing RAB Board, the rigid weather defence barrier by James Hardie. Designed as a high-performance weather barrier, RAB Board is a fibre-cement sheathing installed behind external cladding or rainscreens to improve the durability, performance and comfort of the building.

Water Barrier

RAB™ board is classified as a Water Barrier in accordance with the equivalent water barrier classifications within AS/NZS 4200.1

Condensation Management

RAB™ board is classified as Vapour Permeable when assessed using the Vapour Permeance classifications of AS/NZS 4200.1 based on testing in accordance with ASTM E96, and appraisal from BRANZ.

Fire Safety

RAB™ board is suitable for use where non–combustible materials are required in accordance with C1.9 of the National Construction Code (NCC). James Hardie building products have been tested by CSIRO in accordance with AS/NZS 3837 and are classified as conforming to Group 1 material (highest and best result possible), with an average specific extinction area far lower than the permissible 250m2/kg, as referenced in Specification C1.10a of the National Construction Code (NCC).

Both one and two way fire rated wall systems are available with the RAB™ board when used as part of an external wall system. This will depend on the wall configuration and internal materials used. For more information refer to the James Hardie Fire and Acoustic Rated Walls Application Guide.
When RAB board is installed in conjunction with fire rated plasterboard, the fire rated plasterboard should be installed direct to the stud framing system, and RAB board installed over the top. Increase the length of the specified screw by the thickness of the plasterboard to ensure adequate embedment.

For more information refer to the James Hardie Fire and Acoustic Rated Walls Application Guide.

Energy Efficiency


RAB™ board is classified as an Air barrier in accordance with ISO 9237-1995 and may contribute to achieve energy efficiency requirements, due to reduced air-leakage of conditioned air, which is supplemented with sufficient mechanical ventilation to achieve occupant comfort air-change rates.


When a vented or ventilated cavity system is installed in conjunction (such as vertical top hats with open weep holes, vents or flashings) with RAB™ board, the primary wall structure is physically separated from external heat sources. RAB™ board ensures that the warm air within the cavity does not enter the building, and is instead drawn upwards and out by convection while cool air is drawn.

How does it work?

RAB works by equalising the air pressure within the external wall cavity, making buildings airtight and providing superior weather-tightness, structural bracing and fire protection. This differs to traditional flexible wall underlay, which can struggle to perform in challenging weather conditions.

RAB Board not only provides a rigid air barrier, but due to its patented CoreShield sealer technology, it provides an all-in-one rigid, water-resistant and a vapour permeable membrane, meaning there is no need for additional sarking or treatment.

RAB board or HardieWrap?

But how do you know when to use RAB board versus HardieWrap? Here’s this simple diagram to answer that question for you…

Features and benefits of RAB board

  • Superior weather defence behind ventilated rainscreen cladding
  • Suitable for non-combustible construction
  • Resistant to moisture and the elements
  • Breathable, allowing water vapour to get out
  • Provides 180 days protection during construction
  • Withstands wind pressures up to 7kpa
  • 10 year warranty