Rainscreen Construction Principle (Part III)

Rainscreen Construction Principle

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.

Rainscreen Construction Principle (Part II)

Rainscreen Construction Principle

Rainscreen Construction Principle basic idea is to have an exterior surface or cladding layer that can break the force of sideways, wind load, water movement, resulting in preventing water penetration into the building’s structure. For most of the buildings, from modern to traditional ones, water is the biggest enemy. However, producing a complete watertight cladding system is challenging. Thus, manufacturers started working on the rainscreen construction principle decades ago to provide better protection for the constructions in the city. Rainscreen comes in different styles and types. One of the most popular types is the ACM panels or ACP materials used widely in the modern era. These particular products offer numerous advantages along with their waterproof characteristics.

In the rainscreen construction principle part 1, we discussed the basics of these practical systems and their structure that engineers designed for better watertight characteristics. This article covers essential information about this principle that anyone in the building industry must know.

Rainscreen Construction Principle Types

The rain screen construction principle is based upon two distinct and separate barriers on the building’s cladding. The outer barrier controls most rainwater while the inner leaf performs multiple functions, including moisture and air barrier, insulation, and the structural wall. The outer section allows the water to penetrate through open joinery, and the volume of the penetration depends on the design principle. This is where two distinct types of products come into the picture: the Drained/Back-ventilated and Pressure-equalized/Compartmented systems.

Both rainscreen systems are available in ACM panels cladding materials and different siding for the facade. They use the principle of controlling water leakage without stopping it from penetrating through the exposed outer surface completely. However, the internal design of both systems functions differently based upon the approach. Moreover, the Rainscreen construction principle has been generalized and consolidated into one unified product in specifications combined with both types’ characteristics. For complicating and confusing matters, the water, and air resistance standards from the traditional building cladding systems are applied to these modern designs and specifications of the exterior material’s exposure. Placing the water and air tightness codes on the outer surface of the barrier contradicts the underlying fundamentals of the Rainscreen Construction Principle. Now let’s get to the fundamental of each system.

Pressure-Equalized/ Compartmented Rainscreen

In this article, we focus on the Pressure-equalized rainscreen principle, which is very design intensive. Please read the third part of this article to learn about Drained/Back-ventilated systems for ACM panels.

Pressure-equalized systems are susceptible to design variations and deviations from their design principle. The openings in this system are created uniquely for both static and dynamic pressure equalization allowance across the rainscreen. The essential factor that separates this system from the D/BV principle is the design and the use of the compartmented method within the cavity. The reason behind the compartment is that the pressure equalization can only happen within limited periods and in the case of controlled volume behind the Rainscreen system. This equalization is essential due to the none-uniformity of wind loads, constantly changing across a single cladding of a building.

The vent numbers and their geometry calculation depend on the cavity volume, allowing sufficient airflow in and out of the internal equalized area quickly enough to respond to the ever-changing wind loads. This promotes the pressure differences between the ACM panels or other types of panels used in the system and the internal compartment pressure resulting in equalizing the air pressure on the external cladding and the inner sides of the building facade. If the conditions exist properly, forces causing water movement will decrease; if not, they will be eliminated.

The effective area of the vent holes in this type of rainscreen construction principle depends on three factors which are:

  • The airtightness of the air barrier on the inner section
  • The stiffness of the cladding material and its inner leaf
  • The volume of the compartments that make up the internal air space

The compartments are the essential elements of a proper pressure-equalized rain screen principle. They come with crucial properties, characteristics, and functionalities. Followings are the reasons why these elements play an indispensable role in the PE systems:

  • They control lateral and vertical airflow.
  • They size the volume of the space that the vent openings must be designed for facilitation.
  • The most crucial role of compartments is limiting water infiltration and controlling the water drainage when air-pressure disequilibrium occurs.

The characteristics above show that rainscreens with non-compartmentalized cavities cannot be pressure equalized. However, many of this system’s construction factors and elements are almost similar to the drained/back-ventilated rain screen construction principle. Still, they have several significant and essential differences, which we have discussed in the third part of this article.

Rainscreen Construction Principle (Part I)

Rainscreen Principle

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.

Complete Guide to Installing a Rainscreen

Installing a Rainscreen

Installing a Rainscreen panel is one of the most efficient ways to improve the construction’s envelope’s cladding system. It is a suitable building solution to fit into the modern sustainable, and good-looking architecture trends and provides more accessible installation systems than other cladding materials. Rainscreen systems mainly focus on insulation and moisture resistance properties. They prevent the rainwater from penetrating the facility’s structure, eliminating the risk of condensation-related issues such as mold and dampness. When the water ascertains a way to infiltrate the system, many problems may occur. Damp walls often lose thermal energy and lower the efficiency of the facility. Thus, every building requires a plan for installing a Rainscreen. The most remarkable thing about these materials is that they are practical for refurbishments and new-build projects while being cost-effective and require lower maintenance.

Before Installing a Rainscreen

Installing a Rainscreen requires preliminary steps to ensure if the system is suitable for the particular projects. It is essential to check with architects and local building codes before the procedure starting point. Following all construction codes that apply to the building zone is necessary. Builders should test the material’s sustainability for the projects since various factors and variables can exist during the installation process. Manufacturers always provide instruction for their products for different types of projects which is viral to follow. When the installation instruction differs from the standard codes, it is better to contact the contractor and check if it is still suitable to use Rainscreens for the purpose. Here is the list of before-installation steps that can help individuals in their project management.

  1. The first thing is to calculate the number of requiring cladding materials depending on the net finished dimensions.
  2. The characteristics and properties of the Rainscreen siding must accommodate the local weather conditions and climate.
  3. Using the end seal for covering the ends of existing grains on the new fabricated or cut panels is essential.
  4. The last step depends on the demands of the homeowner. If the homeowner expects permission, it is better to check local building codes and provide a report to ensure the project’s road map.

Steps of Installing a Rainscreen

Installing a Rainscreen whether it is Aluminum composite material or other industrial product, contains standard steps for achieving a better result. If the process is done with precision and by following the steps, the product can be at service for a long time without requiring regular maintenance. Here are the main steps for installing Rainscreen panels for a project that are essential to follow.

  1. The first step is to prevent moisture intrusion with house wrap installation in which following the vapor barrier instruction is essential.
  2. The next step is installing the baseboard, also known as furring strip, using constructional supplements such as stainless screws. During the baseboard installation, it is crucial to ensure the product level.
  3. Along with attaching the furring strips, they need to be aligned vertically on the baseboard’s top with 0.3 meters distance on the center.
  4. This step requires starter clip installation, which includes hidden siding fastener kits on the board. After installing the clips, they should have perfect alignment with the furring strips. Using a chalk line reel for creating a level line can be helpful.
  5. After using a level for ensuring the first board alignment, it is time to install the first Rainscreen Siding board on the clips’ top section.
  6. Designers always recommend placing the hidden siding fasteners into the groove section of the cladding.
  7. Experts drive the stainless-steel screw through the clasp into the strip at a 45-degree angle.
  8. The last step is to use a rubber mallet to align the cladding materials properly, and then builders should set the proceeding siding boards on the top of the fasteners. It is good to have in mind that two pieces of sidings abut against each other, using two pins can be helpful.

Other Factors to Consider During Rainscreen Installation

While installing the buildings on the buildings, some essential factors are considered to provide the panels’ maximum efficiency. Wavering these factors can decrease the system’s quality and can cause further damage to the structure, which will end up in repairing and expenditure increment.

Allowable Shrinkage: Installing a Rainscreen requires installation tightly for each board to leave the minor gaps between the products if shrinkage happens. Mediocre shrinkage needs to be measured. However, this factor varies depending on installation site, method of use, and climate.

Cutting and Drilling: Using special tools such as premium carbide saw blades are recommended for cutting due to the rugged nature of Rainscreen panels. It is better to use point drill bits or foster bits to provide cleaner holes on the boards.

End Sealing: Most manufacturers ship their Rainscreen products with the end grain sealing process with clear wax, perfect for preventing any end checking and conflicting movement.

Finishing: Due to the physical properties of Rainscreens, most of the oil and water-based finishes do not dry appropriately after being applied. It is better to test different product samples on various boards to find the most efficient finish for the demanding project before starting the installation process.

What is a Rainscreen Cladding System?

Rainscreen Cladding System

Rainscreen cladding system is one of the most efficient cladding products in the modern era for construction projects purposes. The system is suitable and fits into the current trendy and sustainable architecture designs and consists of an easy installation system compared to many other cladding materials. Thus, knowing the advantages and functionality of Rainscreen products is essential for creating an appropriate exterior for a building. An inappropriate facade cladding insulation system can entail considerable energy loss in commercial buildings and private homes. In contrast with many inadequate cladding systems, Rainscreens products can favor energy saving due to its air cavity on the facility’s exterior section. With the combination of Rainscreen techniques with a proper facade insulation method, it is possible to provide the building with numerous benefits and advantages, such as increasing the sound and thermal insulation and other significant properties

How Does the Rainscreen Cladding System Work?

The Rainscreen cladding system contains a bearing wall, insulation surface with a layer with sufficient substance, and a fixed cladding material on the building, which utilizes a supporting structure. Due to this system’s perfect design, air cavity presence between the cladding material and the load-bearing wall allows the facade to have continuous ventilation. Depending on the projects, it is common to find an insulation layer between the cladding and the load-bearing wall. In some cases, the load-bearing wall itself can insulate the system, and in others, it is possible to place the insulating material inside the facility.

  • Load-bearing Wall: The cause of using a load-bearing wall is to ensure the stability of the facility. The design must create enough strength to support the cladding system’s weight and the wind load that transmits through the structure. The load-bearing wall can contain concrete, wood, or brick, among other practical materials. The essential factor is to ensure the wall supports can overcome the cladding material’s weight per square meter.
  • Air Cavity: The air cavity, which has an opening on the bottom and the top section of the exterior system, allows air’s constant circulation. Protecting the gaps must be precise and correct to prevent water infiltrations since water can decrease the insulating product’s efficiency. A ventilated flashing involves the facade’s lower opening to allow ventilation and avoid small insects’ entry. In contrast with the lower section, the top flashing or the upper beginning includes metal profile installation to prevent water infiltration while leaving the requiring space for continuous ventilation. For ensuring the air cavity efficiency, it is essential to create at least 2cm width in the cladding’s tightest part. Additionally, the minimal surface of ventilation can vary depending on the latitude of the facility.
  • Insulation Layer: The insulation layer can be both inside and outside of the building. However, it is better to install it on the exterior section of the load-bearing wall to ensure more efficient structural movements performance. When installing the insulation layer inside the facility, the surface is no longer part of the Rainscreen cladding system, and it will not benefit from the ventilation properties. Regarding the insulating material for this system, there are several options available. Designers choose the thickness of the material depending on the insulating capacity and the application requirements.
  • Cladding Material: Many materials are suitable for cladding, such as ceramic, wood, metal claddings, or even natural slate. The most crucial thing for choosing the cladding material is its resistant, durability and quality that completes the efficiency of Rainscreens.

Advantages

After defining and knowing the structure and functionality of Rainscreen cladding systems, it is essential to know the main advantages that these products provide for the buildings. Followings are some of the most noticeable benefits of these systems.

  • Avoiding Condensation and Humidity: The Rainscreen cladding system is perfect for reducing condensation and humidity both from the facility’s interior and exterior sections. The system’s air circulation is ideal for creating an extra protection layer and removing the possible water infiltration that can find a way through the joints.
  • Extending Lifetime of the Facade: The system that provides air cavity improves the cladding durability since it protects the products from humidity.
  • Reducing Structural Movements: The air cavity maintains the stability of temperature in the construction envelope and prevents the risk of cracks and other issues. Since the system is resistant to temperature changes, it is less liable to experience colossal expansion and contraction movements.
  • Thermal and Sound Insulation: With the combination of the insulation layer and the cladding system, the thermal and sound insulation improves significantly. Acoustic and thermal insulation has a significant impact on health since it decreases environmental pollution.
  • Energy Efficiency: The Rainscreen systems make the cooling and heating process much more manageable in warm and cold seasons and play an essential role in saving energy. Thus, the energy expenditure can decrease about 30% to 40%.
  • Low Maintenance: One of the considerable advantages of the Rainscreen cladding system is that it requires almost zero maintenance, especially when the designer chooses a material to withstand harsh weather conditions.
  • Adding Value to the Facility: The durability, energy efficiency, and low maintenance of the Rainscreen systems can recover the building’s initial investment. Thus, these systems are the perfect choice for new constructions and renovation projects in residential and commercial facilities.