Integrated Water-Intrusion Management Solutions for Multifamily Properties  

Over the past several years, construction of multifamily residential properties has increased to accommodate changing demographics both in cities and suburbs. The combination of Millennials moving into their own dwellings—often now with new families—and Baby Boomers moving from the suburbs to cities has kept the multifamily residential sector going strong.¹ Multifamily construction refers to anything from two-unit duplexes and townhomes to apartment and condominium complexes with hundreds of units. In short, multifamily residential properties are big business, both for architects and builders.

All images courtesy of TAMLYN

Modern multifamily residential projects often include several types of exterior cladding, each of which may have different assembly requirements that can extend project time and cost. Single-source integrated water-intrusion management solutions ensure that cladding and trim all work together to keep the building safe and dry.

When architects are tasked with building multifamily units, water-intrusion management strategies can take significant time and effort in the project. After all, moisture management is increasingly being understood as a critical aspect of building design and construction. When done properly to address the local climate, a good moisture management system can help protect the building structure, extend the life of exterior cladding and paints, and protect the building against everything from mold and rot to insect infestations. When not done properly, the opposite can be true, and the consequences can result in structural damage to the building and health hazards for building occupants, both of which can be dangerous and costly.

Moisture typically gets into a building in three different ways:

1. external sources, such as rain, snow, and ice;
2. internal sources, such as burst pipes; and
3. construction sources, such as damp materials or poor workmanship.

All buildings that are exposed to exterior moisture are at risk of water intrusion. The combination of wind and gravity—and the near certainty of eventual cracks—means that water will find a way to get in. A fault in the actual building design, for example, can inadvertently trap water in a way that directs that moisture back into the building rather than off of and away from the building. Alternatively, building professionals may fail to take into account certain aspects of the site, and that results in water intrusion. A building may get stronger wind exposure than expected, and when it rains, the wind may push water into vulnerable spaces. Internal sources, such as burst water pipes or building occupants who fail to maintain the building or generate moisture from within the property, can also cause moisture damage. Finally, moisture can get in when builders or contractors simply do not secure the building in a way that they are supposed to, either by installing something improperly or through substandard work. Regardless of who is responsible or how it happens, when moisture gets into a building, it is a bad situation. As such, a good moisture management plan and system can help prevent future problems. In this course, we will focus on external moisture management.

For the most part, builders in climates with more predictable rain and snowfall such as the Pacific Northwest or Northeast tend to understand the importance of moisture management systems and know how to incorporate them into projects. Between building codes that require the protection and general experience with wet weather, good moisture management practices are becoming standard in these parts of the country. Builders in hotter and drier areas, however, have not been overly concerned with such practices since they have not had to worry much about them. Local building codes may not require as stringent moisture management for buildings in drier climates; however, changes in weather patterns have meant that buildings in these areas are not protected when they need to be. Across the country, moisture management strategies are increasingly being included in building design, and this includes multifamily residential projects.

Projects with multiple cladding materials, such as the stucco and fiber cement shown here, often require different water-resistive barriers (WRBs) or assemblies between the sheathing and cladding. This can result in increased installation time.

Moisture and water-intrusion management systems include a combination of water-resistant barriers (WRBs) that protect the building assembly, rainscreens that include furring (wood, metal, plastics), exterior facade materials, and some form of exterior trim. WRBs, also known as building wrap, protect the building structure by providing a barrier between outside moisture and the interior structure. When properly installed, the WRB will shed any water that gets through the outer facade materials and let that water drain out of the assembly if rainscreen materials are applied on top of the WRB. Trim, on the other hand, can tie the exterior panels and other facade materials together while adding to the building aesthetic. Moisture management also relies on what are known as the 4 Ds: deflection, drainage, drying, and durability.

Deflection, in this context, refers to designs and materials that keep as much precipitation off of the exterior wall enclosure as possible. Roof slope and eaves designs, for example, can deflect water, but so can external cladding. Drainage is important because any water that pools will eventually find a way into the structure. Drainage helps make sure that it is easy for water to get off of and away from the building. Again, roof design is important, especially with adequate overhangs, but so are gutters and a good WRB system in combination with a rainscreen or drainage plane underneath the cladding. WRBs also play an important role in drying the building, and new WRB designs increasingly focus on this critical element. We will discuss how this works a bit later. Another key to drying is the depth of the rainscreen utilized. Finally, an exterior that is durable enough to withstand the elements helps ensure the durability of interior building components. Once moisture gets into a building, the durability of the enclosure is at risk.²

At times, architects specify water-intrusion management products from different vendors for multifamily residential projects that are designed with a variety of different surface materials. For example, a building exterior may combine sections that are made of stucco with sections of fiber cement panels. In this case, the two different materials would require two different water-resistant barrier types or assemblies to go in between the base sheathing material and the facade material. Using materials from different suppliers can result in longer project times since installation practices may differ between products; however, with new products that can be specified from a single manufacturer and applied to the whole project, regardless of the overlying material, architects and builders can save considerable time on projects. Larger multifamily residential units that require different siding and facade materials often need to be tied together in different areas to ensure a comprehensive water management system. Some of the solutions that are being offered today are integrated rainscreens with WRB wraps and two-part extruded aluminum trim that help drain exterior water. The benefits of these solutions are that they are aesthetically pleasing, simple to specify, and easy to install across many different applications.

Water-Resistant Barriers (WRBs) and Rainscreens in Multifamily Residential Projects

Modern multifamily residential projects are increasing across the country, whether for rental units, condos, assisted-living housing, or even college dormitories. In some urban areas, they are part of densification plans that ease housing shortages and provide more rental units, and as such projects are designed to meet key constraints, including building codes, low cost, and efficient construction. While the exterior styles may differ, the general structural elements tend to be similar and include basic framed block structures covered with fiber cement cladding, metal, stucco, brick, composites, or wood. Many projects combine materials for unique designs, whether that means brightly colored rainscreen panels paired with wood or any other design to help the building fit into its environment. Water-intrusion management strategies for these new multifamily projects rely on rainscreen assemblies in many instances to keep water away from the building’s interior structure.

Rainscreens Basics

A building’s exterior serves as a frontline defense against rain, snow, and ice. But water is tricky because it moves along surfaces and finds its way into cracks. Throughout the year, buildings can be exposed to rain and wind, which pushes water in random directions across the exterior. Snow, ice, and even dense fog can impact the exterior, and when that moisture turns to liquid, it will inevitably find a way to seep into whatever exterior material the building has as cladding.

Building exteriors are not designed to be 100 percent watertight, and even if that is a design consideration, building materials crack over time, others are porous, and many require sealants in between sections. For example, concrete and brick easily absorb water, and in environments with cold winters, the freeze-thaw cycle can mean that these materials will crack—and water will find a way to get into those cracks. Other exterior materials are at risk too. Metal panels, for example, require sealant to form a waterproof surface, but sealants can degrade when exposed to heat, sunlight, and freezing temperatures. Wood panels are also susceptible, whether through cracking, breaches in the sealant, or warping. In short, it is generally understood that no matter what the exterior design or material of a building, some water will likely make it past the first layer. The trick is making sure it does not get to the wall assembly.³

Rainscreen systems, which include exterior panels (cladding), a small drainage gap, and a WRB, prevent water from reaching the building structure. As noted above, while exterior panels provide that first line of defense, they are limited when it comes to being waterproof. Their job is to deal with water that hits the surface and direct it off of the building exterior. Some precipitation may simply bounce off the panel. Some precipitation may move sideways across the cladding surface from wind or downward from gravity. What is important is that moisture be drained off of the surface and directed away from the building.

While siding and rainscreens serve as a first line of defense against water, most builders understand that at some point in the building’s lifetime, some water will make its way past the rainscreen. Different rainscreen systems handle drainage differently, but for many, water that does make it through the cladding is then directed so that it runs along the backside of the cladding and then out through a space at the bottom of the wall. This air gap is critical in that it provides a way for the water to escape, and it also helps the wall dry.

Underneath the rainscreen and on the other side of the air gap, a WRB provides the next physical layer of protection against moisture and helps keep moisture away from the wall assembly. For buildings that have sheathing, the WRB is installed between the siding (rainscreen) and the sheathing; if there is no sheathing, it is installed between the siding and the studs.

Shown is an example of a rainscreen system, including the cladding, air gap, and water-resistant barrier (WRB).

Rainscreens as Part of a Moisture Management Strategy for Multifamily Residential Projects

When we talk about rainscreens and moisture management systems for multifamily projects, one of the more challenging issues arises in projects with multiple exterior cladding styles that need to be seamlessly integrated. While the exterior aesthetic is one side of the story, the other is that these different exterior styles often require different cladding assemblies. So, while the WRB base layer typically stays consistent across the project, cladding assemblies can change, and that means additional steps during installation and opportunities for error.

A good example of this is an exterior that includes both fiber cement lap siding and fiber cement panels. Fiber cement lap siding can attach directly to the WRB, but fiber cement panels need to have a furring system under it. Often, both materials are used on the same multifamily project, and that means that the project requires labor, time, and material costs to install the furring system for the fiber cement panels. In addition, the furring means that assembly thickness will vary, and that impacts detailing between the different materials. This, in turn, can make moisture management even more difficult to address. We will talk more about this later when we discuss the role of exterior trim in water-intrusion management systems.

WRBs come in a wide assortment of materials and designs, and each manufacturer has its own take on the product. For example, the material may be a type of building paper, plastic, asphalt felt, rigid foam insulation, or any number of other options. Most WRBs are vapor permeable, which means that they allow the wall assemblies to dry when necessary.

Each exterior rainscreen cladding material and interior WRB tends to have its own set of challenges, whether in terms of how well it repels and drains water, how the exterior panels are attached to the building, or how well the WRB works at attachment and penetration points. Whatever the case, installers need to be familiar with the product and know how to keep it watertight.

Detailing is impacted when a single project has different material thicknesses.

Integrated Rainscreens with Permeable WRBs: Versatility for Siding/Facade Applications

The building industry has come a long way with improving water-intrusion management for different projects, and multifamily buildings are no exception. Many new designs routinely incorporate a combination of rainscreen cladding on the exterior and WRBs to protect the structure. But moisture is still a problem that needs to be taken very seriously to avoid structural damage, shortened life of paints and cladding, and the potential health hazards that stem from rot and mold. As noted earlier, one of the more common reasons that structures suffer from water intrusion is a mismatch between rainscreen materials and WRBs, and the complex task of making sure specified products work together in a project. A few manufacturers have started to address this challenge with integrated systems that allow builders to specify rainscreen and WRB materials that have been designed together as one material.

While integrated systems will vary between manufacturer, the common goal is to provide a moisture management system with building wraps and accessories (e.g., sealant, tapes) and an attached rainscreen system. Essentially, an integrated system provides builders one-stop shopping from a trusted supplier.

New integrated moisture management systems tackle water intrusion in a variety of ways. Some suppliers have focused on finding ways for building wrap to drain water from the surface more quickly, or through better seam sealants and application techniques.

New designs in drainable building wraps have two key layers: a water-resistant layer and a drainage gap that helps water quickly drain from behind the cladding. The combination of these layers is considerably more effective at removing water than traditional wraps, which are designed more so to keep the water out of the structure but not to specifically drain it.

Another change in moisture management systems involves the building wrap seams, which need to be taped properly to prevent water intrusion. Building wraps, and especially drainable wraps, need to be applied in a shingle style, starting at the base and working upwards. This layering style helps ensure that water does not get into the seams as it runs down the wrap. Drainable wrap, however, presents a challenge when it comes to securing a tight seal because of the drainage gap. If the wrap is not applied properly, taping gaps can form, and eventually water and debris can get caught in the gaps. If this happens, the tape can fail, and the wrap will be more prone to detach from the building structure.

With an integrated system, the manufacturer will provide a tape that is designed to seamlessly and securely seal the wrap. For example, a tape may be double sided to ensure the best adhesion and avoid potential tape gaps.

Benefits of an Integrated System for Multifamily Residential Projects

Integrated systems have numerous benefits for multifamily projects, namely in terms of the time and cost savings that come from using a single solution for multiple material applications and from specifying from a single source. Let’s take a closer look at some of the other advantages of using an integrated moisture management system.

• A single solution for multiple material applications means that builders can avoid the problems that come from different cladding assembly attachment requirements. For example, rather than needing both a WRB and furring strips, which results in uneven assembly thicknesses, integrated solutions allow for a single WRB that works with all cladding options from the same supplier.
• Single-source specification removes any uncertainty about how materials will fit together and eliminates project delays that frequently happen with multiple suppliers that have different delivery timelines. This in turn can save on overall project costs and help ensure that project components are installed on schedule.
• Integrated moisture management systems are easy to install. With one-stop shopping, all required components are guaranteed to work together, which can make installation both quicker and easier.
• New permeable WRBs are designed to optimize drying time. This adds to their versatility when used with associated rainscreen applications.
• Finally, permeable WRBs are proving to be high-quality, durable products that protect the building structure better and longer than traditional materials.

For multifamily residential projects, especially larger-scale projects, each of the above points can help with cost savings when compared to projects that use older materials sourced from multiple suppliers.

Extruded Aluminum Trim, Building Exteriors, and Moisture Management

Extruded aluminum trim is typically used by architects to add clean details to a project’s interior and exterior and complement a moisture management system. For exteriors, extruded aluminum trim can help provide aesthetic variety and cohesion for exterior panels and other facade materials. Some manufacturers also supply moisture management solutions that complement their trim lines and help meet code requirements.

As discussed earlier, builders of multifamily projects are increasingly including moisture management systems as a way of protecting the building assembly, increasing the lifetime of the building in general, and improving the health and well-being of the building occupants. Keeping water and moisture out of a building is a high priority, especially in regions where rain, wind, and snow are common, but also in areas where weather patterns have been shifting and precipitation is increasing. Exterior cladding, such as rainscreens facades that serve as a first line of defense against moisture, combined with a properly installed WRB that protects the building assembly and allows any moisture that gets through the cladding drain out of the building system, helps keep a building dry. But an often-overlooked aspect of the water management system is the trim.

Trim is an important aesthetic aspect of any building, but it can also complement moisture management, either by deflecting water to more protected parts of the building’s siding or aiding in water drainage off of the building. Extruded aluminum trim is a popular choice for many different projects, from single-family and multifamily residential to light commercial. It is sustainable, relatively inexpensive, generally easy to install, durable, and delivers a clean, modern aesthetic when used in conjunction with certain exterior cladding. Moreover, it is usually designed to work with siding from a wide range of manufacturers, and it can be used in many different ways depending on the project.

On multifamily residential projects, extruded aluminum trim offers modern aesthetics, durability, and sustainability, all while adding to the building’s moisture management system. It also has the benefit of easier and faster installation, which is a welcome feature for any project but especially for larger-scale buildings.

Modern trim is often used on multifamily residential projects to provide clean lines as well as assist with water drainage.

Aluminum Trim Properties

Before we dig into how extruded aluminum trim complements a water intrusion strategy, it helps to understand some of the basics about why extruded aluminum is a popular material for architectural projects. There are several reasons, which range from it being readily available in both raw and recycled forms to its overall versatility. Aluminum is derived from mined bauxite and processed into billets that can eventually be heated and rolled, extruded, or formed into a wide range of shapes for any number of different functions. Older aluminum can also be melted down and reused, which adds to the overall sustainability.

Aluminum’s qualities of being lightweight, durable, and recyclable all contribute to a project’s sustainability goals. Lightweight aluminum products have lower shipping costs than other heavier materials, and this can lower project costs overall. Aluminum is also highly resistant to rust, especially when coated properly, so when an aluminum product is used on a project, it is understood that it will last a long time.

Aluminum production is fairly straightforward, with heated aluminum billets that are then extruded through specially shaped dies to form architectural components such as trim. Typically, these extruded trim products are made from one of two different methods, each of which may be used for different aspects of an architectural project. Type 6063, for example, is an alloy of magnesium and silicon, where as Type 6063-T5 is a special architectural alloy that is significantly stronger thanks to an artificial aging process and heat treatment. Architecturally, alloy is useful because it can easily be finished in a way that best suits the project in which it is being used, whether that means painted, color coated, or anodized.

Benefits of Using Extruded Aluminum Trim

6063-T aluminum is a great choice for extruded aluminum trim profiles and a good fit for multifamily residential projects for several reasons. First, the material itself is lightweight, strong, and durable. Second, aluminum trim can easily accept finishes that enhance the material’s durability, all while adding to the aesthetic of the project. Extruded aluminum trim is typically available with finishes that meet most project budgets and styles, with standard pre-colored finishes, primed and ready-to-paint options for custom colors, and anodized finishes for a more metallic look. Regardless of the finish, extruded aluminum trim profiles easily add to the overall aesthetic and performance of the building.

In addition to its durability and aesthetics, aluminum is good for architectural products because it is weather tolerant, rust resistant, and noncombustible. In comparison to other materials that may not even offer these benefits, aluminum is also fairly inexpensive. All of these characteristics are desirable for buildings in general, and they add to the goals of multifamily residential properties that need to be designed for longevity and long-term sustainability, energy efficiency, and moisture management.

Extruded aluminum trim profiles are typically available in a range of different profiles that can address different design styles and exterior panel materials. Profiles will include both vertical and horizontal options, as well as inside and outside corners.

Extruded Aluminum Trim as Part of an Integrated Moisture Management System in Multifamily Residential Projects

While extruded aluminum trim profiles function as a key design aesthetic to provide clean lines and corners, they can also play a role in an overall water-intrusion management system in multifamily units and other larger projects. Extruded aluminum trim can include vertical drain channels on vertical profiles and shingle-style design for horizontal profiles. These profiles, along with two-piece systems, can provide an important piece of a water management system. Some manufacturers are now providing trim profiles that are designed to be easily integrated with their rainscreen systems.

These new systems:

• make installation quicker and easier for builders;
• reduce overall project costs;
• provide a a one-stop shop from a single manufacturer;
• allow architects to design aesthetically clean exteriors that also help protect the building structure; and
• meet building code requirements for water-intrusion management.

To recap, managing water intrusion is a challenge for most buildings, and multifamily projects are no exception. In fact, some multifamily designs make moisture management from external sources more challenging than for single-family homes or other projects. Whether larger, apartment-style buildings or townhouses, structures built with appropriate moisture management systems that include rainscreens and properly installed WRBs that enhance drainage tend to have fewer moisture-related problems and last longer than buildings that ignore this critical aspect of design. Moreover, projects that take advantage of integrated systems from a single supplier benefit from knowing that components are designed to work together, which tends to mean no surprises during installation and thus overall quicker installation. Extruded aluminum trim fits into the integrated water-intrusion management system as well.

Extruded aluminum trim is available in a wide range of profiles and finishes, and it can be used as a design feature that breaks up the monotony of exterior cladding and as a moisture management feature for a variety of different siding styles. Most often, multifamily projects have fiber cement panels as their siding, but some projects include stucco, metal, composites, wood, or brick. Out of these materials, extruded aluminum trim can be used with all except for brick. Most manufacturers have developed extruded aluminum profiles to work with fiber cement, but the profiles can be paired with other materials as well.

One of the main benefits of two-piece extruded aluminum trim is that it is easy to use for different applications and claddings, which makes it a good choice for multifamily residential projects, especially when moisture management is a big concern. Two-piece extruded aluminum systems make on-site installation easy, even when there are different sidings being used. The simple process of installing the base trim component and being able to easily insert the second piece speeds up the installation time and reduces errors.

Two-piece aluminum trim works to protect vertical joints in siding and provides a clean, smooth seam. Two-piece trim is also easy to install.

Two-Piece Extruded Aluminum Trim in Action

Let’s look at two different situations where a two-piece aluminum trim situation would be beneficial. On the smaller building scale, a garden-style building provides a good case of where aluminum trim can play an important role in a moisture management system. Garden-style buildings are often used for condominiums and rental apartments and designed in a townhouse style. Most importantly, they usually are complemented with basement units. Garden-style buildings may have units connected or built very close together; either way, water runoff tends to be a problem. If, for example, the roof is connected, there is a possibility of water pooling in between units, and eventually that water will get into the building. Alternatively, adjacent buildings may suffer from water runoff from neighboring buildings splashing against siding or not being properly drained away. An integrated moisture management system that includes a vapor-permeable, quick-drying WRB and exterior cladding detailed with extruded aluminum trim designed to prevent pooling and direct water runoff away from the building can help preserve the overall life of the building. In doing so, it also helps prevent basement units from water intrusion.

Garden-style buildings benefit greatly from thoughtful moisture management systems that include quick-drying WRBs and exterior cladding with extruded aluminum trim.

A larger-scale building such as a midsize or high-rise condominium development may have different priorities. A building with a large exposed surface, clad in rainscreen panels, has two issues. One is that panel and trim installation will take up a considerable amount of build time if products end up being incompatible or if trim installation requires different techniques for different parts of the building. If a two-part aluminum trim is used—specified from the same manufacturer that supplied the rainscreen system—the risk of delays is likely to be reduced. Second, some water will inevitably be pushed off of the building face and into the gaps between rainscreen panels. If the water is not properly channeled off, it can make its way into vulnerable areas between the rainscreen and the WRB, where it may pool and eventually cause problems. Corner and vertical extruded aluminum trim profiles, however, are designed to complement the rainscreen system by channeling water down and out of the building structure. These two systems can work together to help keep the building dry.

Conclusion

When it comes to buildings, water intrusion is a huge challenge to manage. Multifamily residential projects present their own set of challenges, with designs that include a variety of different cladding materials. When different cladding materials are used, there can be a mismatch between WRB requirements (e.g., furring or not), which can cause problems with water intrusion. Several manufacturers have addressed this problem by creating integrated rainscreen and WRB systems that do not require furring. This means that the basis of the wall assembly will be consistent across the project—and that translates into improved moisture management.

Extruded aluminum trim can work into this integrated system as well. Trim provides design aesthetics to multifamily projects, all while enhancing the moisture management system by strategically draining water from the exterior down to the ground. Where the integrated rainscreen and WRB system can give architects the option to do one-stop shopping to protect the building assembly, extruded aluminum trim provides one-stop shopping for all of the details needed for the siding and facade materials. The trim can be used for each component on its own and for transitions (vertical, horizontal, or corners) between the components.

Advances in both integrated rainscreen and extruded aluminum trim systems offer architects and buildings increased confidence that all components of their moisture management system will work together, thus saving time and costs.

END NOTES

¹Hanamura, Deborah. “Multifamily real estate trends for 2019 and beyond.” Building Design + Construction. 17 April 2019. Web. January 2020.

²Kesik, Ted J. “Moisture Management Strategies.” Whole Building Design Guide. 16 August 2016. Web. January 2020.

³Barger, Cary. “Understanding rainscreen wall systems.” Building Design + Construction. 13 December 2016. Web. January 2020.

Rebecca A. Pinkus, MTPW, MA, is a Toronto-based communication consultant, writer, editor, and historian of technology. She has been writing for the green build industry for several years and has contributed to more than 40 continuing education courses and publications through Confluence Communications.