There are two types of rainscreen systems: drained and back-ventilated (DBV), and pressure-equalized. Each serves distinct purposes and performs differently, especially in various building types and conditions.
Both of these systems include applying housewrap directly onto the sheathing and then installing a cladding system, creating a drainage space in between. But they do different things with that space.
Pressure-Equalized Rainscreen Systems
Pressure-equalized rainscreen systems are commonly used in commercial high-rise buildings. These systems involve a more complex design compared to DBV systems. The core principle of a pressure-equalized rainscreen is to create specific, calculated chambers within the rainscreen cavity. These chambers are designed to equalize air pressure between the exterior and interior of the chamber.
In this system, the top of the rainscreen cavity is not vented. Vertical cavities are intentionally sealed to allow the chambers to fill with air when exposed to high winds. As the wind fills these chambers, the air pressure inside equalizes with the outside pressure, preventing water from being driven up through the cavity.
Due to their complex nature, pressure-equalized rainscreen systems are often used in high-rise buildings where wind and air pressure vary across different floors. The design must ensure that the air inside the cavities remains balanced, which necessitates a perfectly airtight cladding system. For example, cedar shingles would not be suitable because they are not airtight and could allow air to escape, disrupting the pressure balance.
These systems are ideal for high-wind areas, such as regions prone to hurricanes and tornadoes. Proper installation is crucial to ensure the system can withstand the designed wind loads. Even though these systems are designed to handle wind and pressure, they still include a drainage space to manage any inadvertent water ingress. This drainage space is typically created using a clip system or a combination of clips and rails with foam and sealant that boxes it off in a certain way.
Drained and Back-Ventilated (DBV)
Drained and back-ventilated (DBV) rainscreen systems are more common in residential buildings and are known for their simplicity and effectiveness. All of Benjamin Obdyke’s rainscreen systems fit into this category.
For example, in an open joint cladding system — where you are letting water in and air in, and it can move around in that space and naturally drain down. In a DBV system, the cladding is designed to allow water and air to enter the cavity and move around freely, providing an opportunity to dry out the space and creating a path for moisture.
The biggest advantage of this system is the natural convective airflow it provides. The top of the wall is vented and the bottom is open, promoting air circulation and allowing water to drain down effectively.
This principle remains the same even if the cladding system isn’t open-joint. For example, with plank siding, air and water can still circulate between the laps of the siding, allowing any infiltrated water to drain and dry out.
Drained and back-ventilated (DBV) can be further broken down into two categories:
Vented vs. Ventilated Systems
A vented DBV system features an open bottom with no ventilation at the top, allowing air to move horizontally, vertically, and around corners. This design is often chosen when a fully ventilated system cannot be achieved.
In contrast, a ventilated DBV system includes both an open bottom and top, facilitating better airflow and drainage compared to a vented system. The increased airflow helps manage moisture more effectively, making ventilated systems more efficient in maintaining the integrity of the building envelope.
Choosing the Right System
The choice of a drained and back-ventilated (DBV) or pressure-equalized rainscreen system largely depends on the type of cladding you’re using and the specific conditions of your building site. For instance, open cladding systems, traditional plank siding, and cedar shingles are generally not compatible with pressure-equalized rainscreen systems because pressure-equalized systems require perfectly airtight cladding to function effectively.
Pressure-equalized systems involve detailed calculations and engineering to determine the appropriate air space and design specifics, which can increase costs. The system must be executed precisely to ensure its performance, as any imperfection can compromise its effectiveness.
On the other hand, DBV systems offer more flexibility in terms of materials and installation practices. DBV systems are designed to handle water infiltration more resiliently. They accommodate water behind the siding and utilize capillary breaks to prevent moisture from passing through the weather-resistive barrier (WRB). Additionally, DBV systems allow for effective drying of the assembly after water exposure, which enhances their overall durability.
Ultimately, the choice between rainscreen systems will come down to the cladding type and specific project requirements. While a pressure-equalized rainscreen system can be implemented in residential settings, its advantages are more relevant in high-rise buildings due to the unique environmental pressures and wind loads involved.
If you’re looking for help or a more in-depth look at your rainscreen assemblies, contact us today or request a sample of our rainscreen product!