Rainscreen principle is an industrial product that is used widely in residential and commercial facilities for various purposes. This product utilizes the open rainscreen principle and is a subset of the screened-drained classification of wall designs. It incorporates all essential characteristics that the building industry requires. Additionally, the authentication of the open rain screen is its capability of equalizing air pressure and ventilation allowance.
What is The Rainscreen Principle?
The rainscreen product and principle, as today’s industry knows, owes much of its development to such men as Birkland and Garden. However, the terms open rain screen principle, and rain screen appeared in the 1960s. These respectful men examined five primary forces that cause rainwater infiltration in a wall. They also looked at the existing wall designs and materials that used cavities and interior drainage to control water departure. Thus, they found that if all of the five forces behind the water infiltration through a cladding can be eliminated or controlled, then the rainwater or the water present on the wall will not penetrate the building.
It is essential to note that it is not conceivable that architects or building designers can prevent the exterior section of the facility from getting wet nor guarantee that no openings will develop to permit the entrance of the water. However, researchers prove that incorporating an air chamber into the wall or joints where the air pressure is equal to that on the exterior can prevent rainwater infiltration. In essence, the external layer is an open rain screen that damages the wetting of the facility’s primary wall or air barrier.
Engineers have reasoned that the air pressure difference existing between the exterior and the interior of the wall system results in air currents that carry the moisture or water into the building’s Cladding. Unfortunately, at the first stage of rainscreen development, manufacturers could not produce products to provide a strategy to relieve air pressure differences that the Cladding was experiencing. If any building designer created a moderate pressure, it was incidental. Air pressure was the cause of water infiltration that many had not considered at the time. However, years of research and studies have shown that this force is the dominant contributor to water leakage.
Structure of a Rainscreen
As told, rainscreen provide air ventilation due to their unique structure. This product features three primary components:
- A screen or outer layer.
- A pressure equalization chamber with a perfect sealing system on all sides except at the vent.
- A vent or opening that connects the air chamber to the exterior.
More specifically, for countering other forces that can cause air infiltration, a rain screen has other practical features. Therefore, manufacturers create products that have a more comprehensive design to develop the rainscreen principle fully. The structure of a fully developed main screen contains:
- Screen or Cladding- the screen is a durable material that is exceptionally non-porous and is generally in the form of a panel. This section of a rain screen allows the water to run off both sides of the product.
- Open Joints or Air Vents- this section of a rain screen includes gaps for ventilation. The product features a labyrinth type of interlocking dry joints for controlling momentum, surface tension, gravity, and capillary action forces. For better sealing and more efficient protection, it is possible to use wet seals such as caulk behind the Cladding.
- Air Flow Toward and Out of PECs (Pressure Equalized Chamber)- the primary wall of the rainscreen products is divided into much smaller self-contained chambers. Each PEC size is determined precisely and as airtight as possible. The more profound and more extensive the section is, the more air intake is required. Thus, bigger vents will be needed.
- Chamber Baffles- these are the sidewalls of the pressure equalized chambers that should resist the pressure and wind loads inside the section. Thus, they need to be relatively airtight. Chamber baffles can be any divider such as a structural connector or clips that support the Cladding.
- Air and Moisture Barrier- these barriers create an airtight blockade between the chambers and the inside of the facility. They must be strong adequate to handle the exterior loads from wind and pressure. Some materials can double the air and water barrier for better sealing characteristics.
- Drip Edges, Flashing, and Drainage Channels- drip edges and flashes funnel water out of the pressure equalized chambers and run away from the facility. In addition, rainscreen panels may have feature channels that evacuate liquids that drain along the surface or the back sides of the cladding material such as ACM panels.
- Waterproof insulation- This particular section is optional, and many manufacturers do not utilize them for creating and installing buildings rainscreen panels.
- Inner Wall Structure
If you want to know more about Rain screen principle, you should read the Rainscreen Construction Principle (Part II) article.