Rigid Air Barriers

Rigid air barriers, also known as external sheathing boards, are key components in rainscreen and open façade systems. Positioned behind the outer cladding and ventilation cavity, they form a durable, continuous layer over the insulation and internal lining, offering a high-performance alternative to flexible membranes. While particularly suited to mid- and high-rise buildings facing harsh environmental conditions, they are equally effective in low-rise applications.

Key Features

Condensation Management

Rigid air barriers are vapour permeable, performing similarly to Class 4 vapour permeable membranes. This allows internal moisture to escape through the building envelope, reducing the risk of interstitial condensation and improving long-term wall health.

Durability

When joints are taped and the system is fully sealed, the barrier forms a secondary weathertight layer. This makes it suitable for exposure during construction, protecting internal elements and maintaining envelope integrity even before the final cladding is installed.

Material Composition

Typically made from fibre cement or similar rigid, durable materials, rigid air barriers outperform pliable membranes in terms of:

• Wind resistance

• Structural rigidity

• Fire safety (some are classified as non-combustible)

Additional Protection Options

In more demanding conditions, an additional membrane layer can be applied over the rigid air barrier to enhance airtightness and moisture resistance.

Thermal Performance Contribution

While rigid air barriers do not provide significant standalone thermal resistance (typical thickness: 13–16 mm), they support thermal performance indirectly by:

• Promoting dry wall assemblies

• Preventing thermal bridging from wet insulation

• Improving real-world R-values through moisture management

Applications and Benefits

Rigid air barriers are a staple in modern building envelope design, offering high durability, excellent weather protection, and robust support for energy and condensation management strategies. Their versatility and reliability make them a preferred solution for both commercial and residential projects, particularly where long-term performance and construction resilience are essential.