Overview
There are two main types of membrane used externally in building façades, each having a different primary function.
• Firstly, there are membranes used to create water and airtight seals around windows and along sheathing board to concrete interfaces. These membranes are commonly referred to as EPDM, a reference to the rubber material from which such membranes have traditionally been made. • Secondly, there are membranes used to provide a vapour-permeable, protective layer when wrapped around buildings behind the cladding. These membranes are usually known as Breather Membranes due to their microporous nature which allows the passage of water vapour to the outside of the building.
These two different types of membrane have been designed for the specific purposes mentioned above, and as such, are different in their material composition, with different performance capabilities.
Although there are differences in the membrane performance requirements of the two applications, fire classification is a crucial consideration for all construction membranes. The Building Regulations and Approved Document B require all components of a façade build-up to have a fire classification. When considering membranes for sealing interfaces around windows, doors, and sheathing board edges, it’s helpful to bear in mind what has traditionally been used – ie. EPDM. EPDM has been used because the material is watertight and airtight, both essential properties for it to effectively perform its primary function. With the introduction of Approved Document B, EPDM is no longer compliant on relevant buildings, due to the combustibility of rubber and its high contribution to the spread of fire.
Consequently, new fire-classified materials have now been developed, which, importantly, still have the water and air-tightness properties required for an effective seal around windows and interfaces.
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