Rainscreens for Retrofitting
Updating Existing Structures for Optimal Performance
By David Hohenstern, Technical Manager, Rainscreen, Sto Corp.
(Editor’s note: David Hohenstern is a Technical Manager for Rainscreen® at Sto® Corp. With more than a decade of experience in rainscreen cladding systems, he has designed and executed numerous code compliance testing projects for wind and fire resistance, rainscreen performance, and overall durability and managed third-party code compliance certifications and approvals.)
There is a wide range of factors for why a building needs a renovation. It could be water intrusion issues, delaminating exterior finishes, cold walls, and new fire and energy performance regulations. Many times, it is many issues all at once. No matter what the reasons, a renovation is an opportunity to enhance the building’s performance and ensure the building science is accurate.
Older buildings lack the thermal efficiency of newer buildings, so your retrofit could probably use a new jacket. Just like humans adapt their clothing to environmental conditions, exterior wall assemblies need to adapt as well to endure longer lifespans while protecting against changing weather conditions, safeguarding interior environments, and promoting occupant health and well-being.
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.
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% annually.
• Insulation: an added insulation layer enhances thermal efficiency and limits condensation.
• 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 a rainscreen system, you get an exoskeletal system that supports a variety of architectural finishes, such as glass, stone, wood, and brick, as well as beautiful finishes that allow you to use a variety of colors, textures, and shapes.
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 your building’s first line of defense. Depending on the climate zone and local environment of the building, you’ll want to choose the cladding type 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 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.
• Exterior Insulation: this outer layer of insulation is capable of handling some moisture and drying without degrading or reducing its R-value. Depending on the building owner’s thermal requirements and targets, this layer may be supplemented. Also, energy codes require different degrees of exterior wall thermal performance.
• Venting Profiles: there are several ventilation options available to help direct moisture away from the wall surfaces and to keep out pests.
Over the last 20 years, the number of manufacturers offering rainscreen products has grown. Today, there are several excellent solutions on the market. But choosing the right manufacturer is critically important. Think about if the manufacturer offers a complete system, if the system has undergone extensive testing, if the manufacturer offers on-the-ground service support, and if they have expertise in a particular area you need.
The fewer manufacturers you have to deal with, the better. Ideally, you’ll have one manufacturer that offers all the components required for your rainscreen system. Often, one manufacturer is hired for the aesthetics, another for the air moisture barrier, and another for sub-construction. If something goes wrong, all the manufacturers will point at each other, and you’ll be stuck in the middle. Keep it simple. Find one manufacturer that can provide you with a total solution from the sheathing out because that way, there’s no question who needs to help you address whatever issues may arise.
Not only do you need to look at the manufacturer, you also need to look at the project manager, as project managers are incredibly important with a massive undertaking like a rainscreen installation. They can make your life a lot easier. They can even make you the project hero. 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 your solutions are tailored to the project needs. They’ll ensure you meet all your energy requirements, address structural requirements, and can help you stay on schedule and on budget.
When sourced and installed properly, a rainscreen system functions beautifully, saving you money starting on day one. But what does a modern rainscreen system look like? Something that functional must look functional, right? Quite the opposite. The right rainscreen system gives your architect the freedom to achieve virtually any look.
On your next retrofit, consider proposing a modern, proven rainscreen system. The right one can transform even the oldest building into a modern, thermally efficient work of art.
