Weathering the storm: Rainscreen systems in retrofits

by tanya_martins | November 16, 2024 11:25 am

By David Hohenstern

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A renovation can be triggered by a wide range of factors: water intrusion issues, delaminating exterior finishes, cold walls, and new fire and energy performance regulations. Often, it is a range of issues happening with increasing frequency that indicate it is time for an update. Regardless of what prompts a renovation, it is an opportunity to build back better, enhance the building’s performance, and ensure good building science is followed.

Give that building a jacket

Exterior wall assemblies are much like multitasking performance jackets—enduring longer lifespans while protecting against changing weather conditions, safeguarding interior environments, and promoting occupant health and well-being.

However, sometimes, a building needs a new jacket, and retrofitting for an aesthetic refresh also provides an opportunity to enhance the wall assembly’s performance. Key components needed include proper continuous air sealing and water-resistive barriers, thermal insulation, and a rainscreen ventilation cavity.  These elements collectively form a high-performance exterior wall assembly.

The perfect jacket for a retrofit: A modern rainscreen system

When retrofitting an old building with a new jacket, air sealing is critically important. A continuous air seal is best achieved with careful detailing of the air barrier, particularly at openings and corners, as well as transitions to the roof and foundation. The addition of a rainscreen system then protects inner walls from weather exposure and prevents water and moisture from penetrating the building envelope. The benefits of a modern rainscreen system include:

• Energy efficiency—Rainscreen cladding improves thermal performance, reducing heating and air conditioning costs by up to 40 percent annually.
• Insulation—When done correctly, an added insulation layer enhances thermal efficiency and limits condensation. If done incorrectly, condensation can occur in areas where it should not, leading to moisture buildup and potential damage. There must not be a gap or pockets between the sheathing and exterior insulation.
• Protection—The cladding protects the building’s exterior from wind, rain, and snow, extending its lifespan and reducing maintenance costs.
• Structural stability—The air cavity in the rainscreen mitigates temperature variations, reducing structural movements and the risk of cracks.
• Acoustic insulation—An additional layer of insulation helps block outside noise, which is beneficial in urban environments.
• Design freedom—With rainscreen systems, an exoskeletal system will support a variety of architectural finishes, such as glass, stone, wood, and brick, as well as finishes that use a variety of colors, textures, and shapes.

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Components of a modern rainscreen system

A rainscreen is made up of several key structural components that work together to manage airflow and moisture effectively; these components usually include:

• Outer cladding material—The cladding is a building’s first line of defense. Depending on the climate zone and local environment, choose the cladding type (e.g. fiber cement, metal panel, HPL, specialized render systems, etc.) based on the hazards present and the level of protection needed.
• Air gap or cavity—A ventilated space behind the cladding that helps manage moisture. A modern rainscreen system incorporates a larger air gap of 20 mm (0.78 in.) or more; as compared to traditional drainscreens used in wall assemblies; to promote drainage and drying of wall assemblies.
• Air and water-resistive barrier (AWRB)—This is attached directly to the building’s frame and is the last line of defense against air leakage and moisture intrusion. Depending on the climate, the AWRB may be permeable or impermeable to water vapor. A good rule of thumb is that in humid climates, a permeable AWRB should be used to allow moisture to escape from the building envelope. In dry, cold climates, an impermeable barrier is better suited to keep moisture out. Always factor in local climate conditions when selecting an AWRB.
• Exterior insulation (a building’s overcoat)—This outer layer of insulation is capable of handling some moisture and drying without degrading or reducing its R-value. This layer may be supplemented depending on the building owner’s thermal requirements and targets. Also, energy codes require different degrees of exterior wall thermal performance.
• Venting profiles—There are several ventilation options available, including venting flashings, perforated profiles, and weepholes, to help direct moisture away from the wall surfaces and to keep out pests.

Straighten walls without moving them

When most buildings are built, neither the building owner, architect, or applicator is worried about straight exterior walls. Their primary focus is on everything from the cladding inward. Therefore, the exterior surface inherited from the initial construction is the wall to work within a retrofit. There is a chance it may be straight, but more than likely, it will not be. One of the benefits of a rainscreen system is adding an exoskeleton to the exterior wall, allowing teams to adjust and square up the wall before adding the new cladding.

The cost of a rainscreen system

The budget is always the elephant in the room. A rainscreen system may increase upfront costs, but such investments will reward building occupants and owners with a range of benefits. Among these benefits are:

• Long-term performance—All the components of a rainscreen system work together to ensure optimal performance over the building’s lifespan.
• Durability—These components are also built to last and with an eye toward future adaptability, reducing maintenance and repair costs over the structure’s lifetime.
• Enhanced comfort—A sophisticated exterior designed to deliver thermal efficiency protects the building and the rainscreen from severe weather, making for a more comfortable interior. Improved thermal efficiency offers a payback on the investment via reduced energy costs and consumption, which also benefits the environment.

There is always a delicate balance between performance and cost; however, it is important to consider the savings year-over-year that will be realized with a rainscreen system. The right one can completely transform an old building, making it more thermally efficient and aesthetically pleasing, allowing it to compete with newer construction and design.

According to the National Renewable Energy Laboratory (NREL), deep energy retrofits achieve at least 50 percent reduction in energy usage and usually include building envelope upgrades, building electrification, and energy conservation measures that enhance building performance and occupant value. NREL further states energy lost through opaque envelopes alone is responsible for 25 percent of building energy use in the United States.

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Is the manufacturer important?

In the 20 or so years since rainscreen systems were introduced, the number of manufacturers offering rainscreen products has grown. Several excellent solutions are on the market today, but choosing the right manufacturer is critically important. When considering which product to invest in, consider these questions:

• Does the manufacturer offer a complete system? The fewer manufacturers to deal with, the easier the project will be. One manufacturer that provides everything from the sheathing out is ideal because one warranty will cover the entire system. The last thing specifiers want is to stitch together a piecemeal system and hope the subcontractors have successfully installed them to create a properly sealed envelope.
• Has the system undergone extensive testing? Specifiers will want a widely used, trusted, and, most importantly, thoroughly tested system. One of the most recognized tests for rainscreen systems is the AAMA 509. It was the first North American testing standard for drained and back-ventilated (DBV) rainscreen cladding. It was developed to create a benchmark in DBV rainscreen performance and provides specific ventilation and moisture control criteria. Ensure the rainscreen selected meets this standard.
• Does the manufacturer offer on-the-ground service support? The right company will have project service managers who deeply understand building science and can help dial in the needed systems. They will provide thermal modeling to balance the thermal target with the structural loading and work with the general contractor to ensure the project progresses smoothly.
• Is there a need for a manufacturer with expertise in a particular area? This depends on the specifics of a project. If there is significant water intrusion into the interior of the building, for example, consider a company with expertise in subconstruction. Or, if dealing with extreme weather conditions taking a toll on the cladding, consider a company with more cladding expertise. However, all larger manufacturers have the knowledge and experience to solve virtually any problem. They have seen it all and have the expertise to design a rainscreen system that meets specific needs and ensures moisture does not end up in areas where it can do more harm than good.
• Does the manufacturer offer a wide variety of design options? This is very important. Here is why. If the rainscreen system has limited design options, the architect will be restricted in meeting the aesthetic goals of the project. So, by default, the system’s functionality is being prioritized over the appearance of the building. Also, buildings need to be refreshed every so often. By installing a system with endless design possibilities today, there is the option of updating only the cladding later instead of replacing the entire rainscreen to achieve a specific look. The right product and manufacturer will offer various design options so the client can achieve the look and feel they desire now and in the future.
• Is the system eco-friendly? This is becoming more important with every passing year. Specifiers need a system built for the future that offers lightweight solutions, recycled materials, and incorporates sustainable components. Building codes are getting stricter, and the expectation is that building owners will do their part to be mindful of the environment in new construction and retrofits.

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The importance of project managers

At the risk of overstating this, project managers are incredibly important with a massive undertaking such as a rainscreen installation. Pertaining to project management from a manufacturer and not a third-party vendor, an experienced project manager will facilitate the project from start to finish—from proper cost estimations at the beginning of the project to determining how many parts and pieces are needed for the system, and along the way, coordinating with engineers and other experts in these systems to provide specifications to ensure solutions are tailored to the project needs. They will ensure the project meets energy requirements, address structural requirements, and help stay on schedule and budget.

Beware of the Frankenstein system

As noted above, the fewer manufacturers to deal with, the better. Ideally, one manufacturer will offer all the components required for a rainscreen system. After all, a rainscreen system is a system, not a kit of parts. A Frankenstein system is the total opposite of that. Often, one manufacturer is hired for the aesthetics, another for the air moisture barrier, and another for sub-construction. A Frankenstein system is a setup for failure in the long term. If something goes wrong, all the manufacturers will point at each other while the specifier is stuck in the middle. Keep it simple. Find one manufacturer that can provide a total solution from the sheathing out; that way, there is no question about who needs to help address whatever issues may arise.

Seeing is believing

When sourced and installed properly, a rainscreen system functions beautifully, saving money starting on day one. What does a modern rainscreen system look like? Something that functional must look functional, right? Quite the opposite. The right rainscreen system gives the architect freedom to achieve virtually any look. Here are three real-world examples of the possibilities. Keep in mind that these examples are retrofits.

Cafesjian Art Trust

The retrofit project for the Cafesjian Art Trust was driven by the need to transform an outdated building, originally constructed in 1977, as a warehouse and office space. The plan was to turn the space into a visually compelling museum that could effectively display modern art. The existing facade lacked the aesthetic appeal and functionality required for a museum setting, prompting the decision to upgrade the exterior to better align with the institution’s mission. The solution involved installing an open-joint, drained/back-ventilated opaque glass rainscreen system, which provided a vibrant, customizable facade using shades of blue that mirrored the art within. The colors are fused to the back surface of the glass, making them resistant to fading and unreachable to scratch or abrade. This system allowed for a non-invasive retrofit by using a sub-construction system attached to the existing substrate with bracket connections, enabling the glass panels to connect to a flat plate while maintaining the integrity of the building’s exterior and creating a striking and recognizable appearance. The sub-construction was custom-engineered to support the glass panels and manage project-specific wind load design criteria. Using glass panels enhanced the building’s visual appeal and ensured durability and performance.

Bell Bank

The retrofit project for Bell Bank’s headquarters in Fargo, N. Dak., was driven by the desire to preserve a historic building while modernizing its facade to reflect its prominence. Rather than demolition, Bell Bank transformed an old, underutilized concrete structure into its headquarters. The solution came in the form of a glass back-ventilated rainscreen system that consists of thermal insulation (76 mm [3 in.] mineral wool), with adjustability that came in handy with the existing building’s variable planarity, a continuous (fluid-applied) AWRB, and durable, opaque glass-faced panels, which provided a thermally efficient and visually striking facade matching the corporate colors. This system allowed the architects to re-clad the building, integrating the new design with the existing structure and a newly added adjacent building. The result is a contemporary and elegant addition to the Fargo skyline. 

Innovation Outpost

The retrofit project for the Innovation Outpost at Amarillo College was motivated by the need to preserve the historical significance of the former Amarillo High School building while transforming it into a modern hub for innovation and collaboration. The challenge was to create a structure that would serve the functional needs of a cutting-edge innovation center and reflect the site’s rich history. The solution came in the form of the glass rainscreen system with a mirrored glass finish, which provided the desired modern aesthetic while allowing the building to echo its surroundings visually. This system offered a high-performance, thermally efficient facade that met the project’s design goals and delivered long-term durability. The result is a standout building that fosters creativity and collaboration.

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Conclusion

Consider proposing a modern, proven rainscreen system for the next retrofit project. As heard and seen, the right one can transform even the oldest building into a modern, thermally efficient work of art. Plus, it will perform and save money for the building owner well into the future.

Author

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David Hohenstern is a research and development manager for rainscreen at Sto Corp. He joined Sto in May 2022. He is a voting member of the C17 committee at ASTM, which owns and manages the fiber cement standards used in the Americas; E05, the committee on Fire Standards; and E06, the committee on Performance of Buildings. Hohenstern is a two-time graduate of the Georgia Institute of Technology.

Key Takeaways

Exterior wall assemblies, such as multitasking performance jackets, protect buildings from changing weather, ensuring interior comfort and occupant wellbeing. Just as a person may need a new jacket, buildings sometimes require retrofitting for an aesthetic refresh as well as enhanced performance. Continuous air sealing, water-resistive barriers, thermal insulation, and a rainscreen ventilation cavity can transform a building’s exterior into a high-performing “jacket.” While these upgrades may increase upfront costs in buildings, they offer long-term benefits in durability, reduced maintenance, and enhanced occupant comfort.

 

Source URL: https://www.constructionspecifier.com/weathering-the-storm-rainscreen-systems-in-retrofits/

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