Vapour Permeable is the right choice behind lightweight cladding
Know the facts: 'Breather' products
Traditional ‘breather’ products are vapour barrier (impermeable) products that have been perforated with tiny holes to allow the transfer of air and water vapour. The process of perforating the membrane also removes the ability of the membrane to withstand air and water penetration, making it unsuitable for use behind most lightweight cladding materials unless specified otherwise by the cladding manufacturer materials which require a combination of low permeability and water barrier properties.
As illustrated below in Figure 1, once condensation (water vapour) exists in the building frame, traditional ‘breather’ products take a very long time to allow wood to dry-out to an acceptable level of moisture. This increases the risk of wood decay and mould growth within the building structure and increases the risk of associated health issues within the home.
Key facts - 'Breather' products
Low permeability in comparison to a truly vapour permeable product – typically hundreds of times less
Unable to prevent water entry – not ‘water barrier high’ (unclassified) – not recommended for lightweight cladding
Allows air transport, therefore may allow the entry of more water vapour from the outside environment
While datasheets clearly illustrate that vapour permeable membranes breathe better than perforated ‘breather’ foil products, the actual drying performance of wood is the key to protecting the building structure and reducing health issues associated with moisture content.
Figure 1: The drying performance of membranes
Drying performance of membranes experiment notes: 1. Experiment conducted by CSR Building Products Ltd. 2. Products tested included CSR Bradford and competitor products – 16 samples plus one control sample were tested over 30 weeks. 3. All samples were weighed at the commencement of the test and weekly to determine the change in moisture content. 4. All samples were exposed to the same ambient weather conditions and all joins were lapped and taped. 5. All results remain the property of CSR Building Products Ltd.
The solution is Enviroseal ProctorWrap
Enviroseal vapour permeable products allow water vapour molecules to easily pass through the film, but prevent the entry of liquid water. The result is a product that is ideal for fibre cement cladding as it allows the transport of many times more water vapour than a ‘breather’ product, prevents the entry of liquid water (rain or condensation) and also has the ability to prevent the transport of air which limits the passage of moisture.
Key facts - 'Vapour Permeable' products
Highly permeable in comparison to ‘breather’ products – typically hundreds of times more
Membrane prevents water entry – ‘water barrier high’ – suitable for use behind lightweight cladding
Prevents air transport, thereby limiting the entry of more water vapour by air from the external environment
Vapour permeable membranes help to manage condensation risk by allowing water vapour to easily escape – reducing the risk of moisture accumulation in the building structure.
*In conjunction with sealed joins and penetrations.
BENEFITS DURING CONSTRUCTION
Protects the frame and roof structure from the elements prior to the application of external cladding.
Improves on-site work flow efficiency by allowing internal trades to commence work before the external cladding is applied.
BENEFITS AFTER CONSTRUCTION
Reduces the risk of moisture and mould related issues compromising the structural integrity and health of the occupants.
Improves air tightness which in turn improves energy efficiency, but still allows vapour to escape without condensing on the inside of the building frame.
Protects the interior of the building from moisture and dust entry from the outside environment.
If in doubt choose vapour permeable
As condensation risk is difficult to predict and the consequences of condensation are not easy to manage after construction is completed, selecting a vapour permeable product is the recommended default solution.
Further advice and project specific condensation prediction advice is available by contacting CSR Bradford on 1800 354 044 or via our enquiry form.