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.