How can you tell the difference between a Pressure Equalized Rainscreen and a Drained and Back-Ventilated Rainscreen?

Mar 27, 2023Arrowhead, Arrowhead, Blogs, Project Updates, Technical Information, Vitrabond, Vitrabond G2

It is not possible to tell the difference between a drained and back-ventilated rainscreen and a pressure-equalized rainscreen just by looking at the details alone, because test results are the determining factor in deciding which type of rainscreen system it is. In fact, some of the Arrowhead metal cladding rainscreen systems meet both AAMA 508 Pressure Equalized Rainscreen System criteria and AAMA 509 Drained and Back-Ventilated Rainscreen System criteria, underlining that you can’t visually determine which type of rainscreen you are looking at. 

However, there are some key differences between the two systems that can be identified through closer inspection and understanding of the design and installation principles. 

  • A drained and back-ventilated rainscreen system relies on gravity and air pressure differentials to provide ventilation and drainage behind the cladding. This system typically has a continuous ventilation space behind the cladding and includes drainage openings at the bottom of the assembly to allow water to drain out. 
  • On the other hand, a pressure-equalized rainscreen system is designed to equalize the air pressure behind the cladding, which can help to reduce the potential for air infiltration and water penetration. This system typically includes pressure-equalizing chambers or compartments that are designed to balance the air pressure and prevent water from being forced into the assembly. 

To identify the differences between these two systems, it may be necessary to examine the specific design and installation details of the rainscreen assembly, such as the location and size of the ventilation and drainage openings, the use of pressure-equalizing chambers or compartments, and the sealing and flashing details used to prevent water infiltration. 

In the case of metal panel rainscreen systems, sometimes the perimeter extrusions on a Pressure Equalized rainscreen system might have mitered corners to create that compartment. But this doesn’t always hold true, because the Arrowhead Lean rainscreen system does not have mitered corners yet achieves both the AAMA 508 Pressure Equalized ratings and the AAMA 509 Drained and Back Ventilated ratings. 

In summary, the only conclusive way to determine whether a rainscreen system is Pressure Equalized or Drained and Back Ventilated is to review the test data. This will also ensure you are getting a properly tested system, otherwise the performance will just be assumptions. 

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