ARBO ARBOShield Pro Class B W1 Breather Membrane is a high-performance, vapour-permeable wall membrane designed to manage moisture, resist weather ingress, and support fire performance within modern façade systems. It is intended for professional use across light steel frame (SFS), modular, and traditional wall constructions where breathability and compliance are essential.
The membrane achieves Class W1 resistance to water penetration in accordance with EN 13859-1, providing reliable protection against wind-driven rain during both construction and service life. At the same time, it is extremely vapour permeable, with an sd value of approximately 0.07, allowing moisture vapour to escape freely from the wall build-up. This balance helps reduce the risk of interstitial condensation and supports long-term durability of insulation and structural components.
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From a fire performance perspective, ARBOShield Pro Class B W1 carries a Class B-s1, d0 reaction to fire classification. To maintain this performance, the membrane must be installed onto a Class A rated substrate, a critical specification detail that should be confirmed during design and installation. When correctly applied, the membrane helps limit fire spread across the façade with minimal smoke development and no flaming droplets.
Installation should follow recognised good practice. The membrane is fixed directly to sheathing boards or insulation using appropriate mechanical fixings, spaced no more than 600mm horizontally and 500mm vertically. Stainless steel staples are recommended on timber substrates, while SFS systems require fixings with EPDM washers. Vertical laps should be a minimum of 150mm, with horizontal laps of at least 100mm installed shingle-fashion from the base upwards to shed water effectively.
All laps, perimeter edges, and penetrations must be sealed using compatible ARBOShield Pro Class B sealing tapes, particularly where the membrane also functions as the external airtightness layer. The membrane offers high UV resistance, allowing extended exposure during construction without compromising performance.
When specified and installed correctly, ARBOShield Pro Class B W1 Breather Membrane provides a dependable combination of vapour control, weather resistance, and fire-conscious performance for compliant façade systems.
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