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Understanding Rainscreens
Difference Between D/BV Systems And Pressure-Equalized System (PERS)
To explain the difference lets turn to Rainscreen Cladding: A Guide to Design Principles and Practices (Anderson, Gill).
“The main point to note about the drained and back-ventilated approach is that claddings are allowed to leak, and no deliberate attempt is made to minimize the effects of wind by means of pressure equalization. Instead, the cavity behind the cladding is drained and positive back ventilation is used to promote the rapid evaporation of any rainwater deposited on the inner leaf. The same process is used to evacuate the water vapour which permeates through the inner leaf and, if present, it’s insulating layer.”
By contrast, Anderson and Gill further offer the following differentiation to PERS:
“The essential defining attribute that differentiates PERS from D/BV is the design and use of compartmentalization within the cavity to allow pressure equalization that accounts for the constantly changing wind pressures across the face of any building. This makes these systems much more design intensive."
D/BV Rainscreen Components
- Series of sheets, cassettes , or tiles in a range of materials (collectively called ‘Cladding’).
- Vertical or horizontal support systems for the cladding.
- A minimum allowable width of air space between the outer cladding and inner leafs to facilitate positive back ventilation
- An air/water barrier at the rear of the cavity, generally on the outer face of the inner leaf. The inner leaf is generally the structural building enclosure wall
- Water resistant insulation can be applied to the exterior side of the moisture barrier and is optional subject to the building’s thermal design requirements
Designing A D/BV Rain Screen
The design of any D/BV rainscreen is usually a collaboration between the architect and either a façade engineer or a supplier of rainscreen support systems [Brackets; profiles; Primary and secondary fasteners and associated components] who also supply a systems package including shop drawings and a structural analysis of a specific façade.
The suppliers of rainscreen systems must ensure that the components used in their systems are certified and are fit for use in any specific environment. In the case of New Zealand this means the products are suited for use in a marine zone. While this is not always the environment it is best to use these systems as they have a high level of corrosion resistance.
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