Rainscreen construction principle has become an essential part of the buildings industry over the years. With the growth of technology and engineering, manufacturers managed to produce modern and efficient cladding materials such as ACM panels considered rainscreen systems for the building’s exterior. This principle’s primary purpose is to protect the facility’s structure from damaging elements such as wind loads and water infiltration.
In the first part, we provided the basics of the system, which every customer or specialist in the building industry must know. These practical systems are available in two types: Drained/Back-ventilated, which rely on the ventilation cavity, and pressure-equalized methods, which employ drainable compartmentalization for water penetration limitation. PERS method is functional during pressure disequilibrium and facilitates fast pressure equalization. It also minimizes and under certain weather conditions to eliminate water in the product’s cavity. However, you should read the second part of the article for more information about the pressure-equalized system in the rainscreen construction principle. Moreover, in this article, we will discuss mainly the D/BV and its functionality.
Drained/Back-Ventilated Rainscreen Construction Principle
Drain/Back-Ventilated rainscreen construction principle is a practical method of protecting the facility’s exterior, which is utilized in many cladding materials such as aluminum composite panels or ACM panels with various properties, advantages, and functionalities. This system employs a series of boards, sheet metals, or planks called claddings fixed to vertical support channels or rails. The supports are the outer exposed barriers or leaves.
Joints in the external claddings are open but have a unique design to obstruct water infiltration by wind force or kinetic energy. It is essential to note that engineers create these systems to minimize the infiltration, not eliminating it thoroughly. Water leakage occurred from variable air pressure due to the wind is inevitable. Thus, a considerable amount of water can infiltrate the outer leaf through its open joints. However, the system permits the water to run down the interior surface of the outer barrier with a particular control system by the ACM panels designs including vertical channels or rails combined with water head leaves in a horizontal jointing system which directs the liquid flow to the vertical components. Little wetting in the inner barrier surface can happen, which is acceptable and will cause no issues.
The series of vertical channels have a design to collect the infiltrating water and drain it through gravity action. Additionally, they cross-direct at penetrations to the lower level and external section of the outer barrier. The system penetration should have continuous flashing and detailing to collect and direct water to the external obstacles or redirect it into the vertical drainage channels.
The minimum allowable width of air space known as a cavity between the outer and inner barriers is essential to facilitate positive back-ventilation in the ACM panels. This can promote rapid evaporation of any rainwater deposited in the surfaces of the inner surface of the aluminum composite panels or any other rainscreens. However, cavity depth should be considered to be in addition to the center of cladding applied to the building’s facade not to restrict the ventilation flow.
The internal leaf is typically the structural building close wall. Thus it can accept various construction methods. However, the water-resistant insulation should be applied to the exterior side of the cladding material and is an optional term to the thermal design requirements. The use of insulation is to maximize useable building space and rule out condensation and cold bridging to the interior surface of the inner barrier. Since the Dried/Back-Ventilated rainscreen construction principle is not a pressure equalized system, the aluminum composite materials or aluminum sidings considered building claddings must have a precise design to withstand 100% of the wind load.
Difference Between the Two Types of Rainscreens
D/BV rainscreen construction principle and PERS are both designed to increase the efficiency of the building. However, like any other industrial system, they have their differences.
The most notable thing about drained and back-ventilated systems is that leakage for claddings is allowed, and there is no deliberate attempt to minimize the effects of wind loads. Instead, the cavity behind the cladding material is drained, and positive back-ventilation usage promotes the evaporation speed of any rainwater on the inner barrier.
On the other hand, the main point about the pressure-equalized rainscreen construction principle is that without relying on sealants or gaskets in the installation process, every effort is made to minimize or eliminate the leakage through the joints. However, there could be some minor leakage into the cavity, and a drainage mechanism is essential. Additionally, positive back ventilation is utilized to increase the evaporation rate of water which permeated through the inner barrier of the ACM panels.