Rainscreen Design Basics

Drained Back-Ventilated Rainscreens

Diagram 1

Minimum amount of water reaches the AWB Barrier.

Cross-section diagram of wind pressure, air circulation, and water drainage in a Drained Back-Ventilated rainscreen system.

Well-designed, tested, drained and back-ventilated systems can stop over 90% of the water that could potentially reach the air and vapor barrier of the building. The remaining less than 10% of water is gradually dissipated through the combined action of gravity (drainage) and air circulation (evaporation).

Pressure-Equalized | Pressure-Moderated Rainscreens

Diagram 2

No water is reaching the AWB Barrier.

Cross-section diagram of wind pressure, air circulation, and water drainage in a Pressure-Equalized / Pressure-Moderated rainscreen system.

Pressure-equalized rainscreen systems completely prevent water from reaching the building’s air and vapor barrier. Pressure equalization is best achieved by compartmentalizing the cavity:

1. 1 Wind enters through the joints of the cladding panels;
2. 2 It instantaneously fills the sealed compartments of the cavity between the cladding and the wall behind it;
3. 3 As a result, the pressure inside each compartment equalizes to the outside pressure.

In pressure equalized rainscreen systems, there are two equal, opposing forces acting on the cladding layer: the outside wind force versus the air pressure of the inside cavity. These opposing forces prevent rainwater from being forced into the cavity.

Note: Because the cladding layer does not block the outside wind pressure (it just transfers it to the compartmentalized cavity), the air and vapor barrier must be designed to absorb the wind load.