Durability with rainscreen masonry wall assemblies

An eco-friendly design to reduce energy costs

Rainscreen fits well into the colorful, modern design of contemporary buildings like the Orlando Hospital ER, while providing a protective external layer that manages moisture and weather.

Another benefit of a rainscreen is its ability to lower energy costs by 30 to 40 percent (Consult Exterior Wall Cladding: Design Principles and Material Choices).  The rainscreen’s ventilated cavity achieves this by increasing thermal insulation, lowering the retention of heat, and reducing thermal and cold bridging, which can lead to condensation and mold growth.

Due seasonal temperature variations, a natural convection process commonly known as the ‘chimney effect’ also occurs within the cavity. This results in the warm air rising and then being replaced by cooler air temperatures during the warmer months. The inverse happens during winter when the air inside the cavity is too cool to rise, but warm enough to surround the building’s interior with an insulated layer of mildly heated air. Other energy-efficient benefits of this effect include protecting the façade’s internal thermal insulation, while helping it maintain maximum efficiency through the reduced possibility of excessive air leaks.

Many of today’s modern structures are currently earning Leadership in Energy and Environmental Design (LEED) credits with the latest, high-quality masonry products. On average, concrete masonry units (CMUs) can reduce greenhouse gas emissions by 3 to 5 percent when compared to wood, with lower heating and cooling costs. The highest-performing insulated masonry systems available on the market have been shown to exceed most stringent code requirements by delivering thermal performances rated at R-16.2.

Prolonged building stability

In addition to adding an extra layer of moisture protection to a building’s façade and increasing its energy-efficiency, ventilated rainscreen wall systems have been shown to prolong the life expectancy of new and upgraded facilities. Reducing decay and peeling of paint are just a few of the advantages. The stable temperatures produced within the air cavity can also help to:

  • reduce structural movements that cause cracks and other structural integrity problems;
  • prevent noise pollution through the addition of layers of acoustic insulation. Some systems even offer a sound transmission class (STC) rating of 61 dB as per testing done in accordance with ASTM E90, Standard Test Method for Laboratory Measurement of Airborne Sound Transmission Loss of Building Partitions and Elements, meaning even loud sounds like stereos, lawn mowers, or traffic cannot be heard from within the building;
  • greatly reduce or eliminate maintenance costs since the dense, tight surface structures of the system’s natural stone veneers are easy to clean and resistant to deicing salts and chemical cleaners;
  • enhance the life expectancy of the building’s façade, which is shielded from moisture and other extreme weather conditions; and
  • withstand wind speeds up to 225 km/h (140 mph) depending on building parameters and the materials used in accordance with ASTM E330, Standard Test Method for Structural Performance of Exterior Windows, Doors, Skylights, and Curtain Walls by Uniform Static Air Pressure Difference.

Creating effective air barriers

Rainscreen wall systems also help eliminate air leaks which enable humid air to deposit moisture on cold surfaces creating mold, decay, and bulk water risks. Therefore, the wall’s air barriers are among the most critical components of a rainscreen’s assembly as they provide an important  critical line of defense against water infiltration.

Without the barrier, air can easily migrate through the system to deposit large quantities of vapor within its walls and then condense to create severe water-related issues. Air barriers stop the flow of air in the wall assembly, no matter if caused by wind or pressure differentials between the building’s interior climate and outside weather conditions. They achieve this by directing the air and water that bypasses the external cladding toward the bottom of the system, where it can drain and then evaporate into the surrounding environment.

Sun protection

Almost all forms of concrete and masonry suffer the harmful effects of the sun unless properly designed and treated. Over time, the constant barrage of ultraviolet (UV) rays and heat can combine to break down the material’s polymers and other bond chains. This can result in the production of a fine dust or powder on the masonry surface, not to mention fading of inferior products.

Made from cement, aggregates, and water, CMUs are versatile, strong and durable, as well as ideal for shielding building faces from problems while remaining lightfast for decades. In fact, some manufacturers even cure and heat treat their units with a thermoset glazing compound permanently molded onto the product’s surface with a gas-fired tunnel kiln to further secure their masonry from the sun.

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