Providing Thermal, Moisture, and Fire Barriers In Harsh Conditions

Critical building systems need to hold up to multiple rigors and demands

By Peter J. Arsenault, FAIA, NCARB, LEED AP

All buildings are designed using a combination of materials, products, systems, and components. Each part is selected and specified to do a particular job, serve a particular purpose, or meet specific criteria. Some are driven by design and aesthetic priorities, while others are driven by functional and performance requirements. The most successful designs are those that allow all of these parts and pieces to work together such that the use of one does not compromise the use of another. In fact, the ideal situation is one where products or components can enhance other materials or systems that are part of the larger building.

This premise is particularly true where thermal, moisture, and air barriers are involved. By their nature, buildings create a barrier or separation between indoors and outdoors. That separation involves restricting or eliminating the passage of unwanted air or water and controlling unwanted heat transfer. The types of products and systems used to accomplish that separation will determine the effectiveness of the exterior enclosure of a building. But more importantly, the attention to all of the areas where those barriers have seams, connections, penetrations, or irregularities determines the ultimate performance and effectiveness of truly continuous barriers. This is true not only in building exterior enclosures for thermal and moisture protection, but also within a building, where fire barriers are required to protect human life and safety. Walls, floors, and ceilings may be tested and rated, but if the construction is not truly continuous due to openings, joints, or other features, then the effectiveness of the barrier is compromised.

There is one other concern for the long-term integrity of barriers in buildings, namely the conditions they will face over the life of the building. Most of the manufactured barriers or systems available are tested and rated based on typical, or average, conditions. But, depending on their location and use, buildings may experience more difficult or challenging conditions. Some locations constitute harsh environments due to regular exposure to salt water, high winds, or heat and cold. Others are in active seismic zones that can impose numerous stresses from multiple minor earthquakes over the life of the building. Hence, the long-term safety and durability of these barriers, and the buildings and people that they protect, are directly dependent on their capabilities to hold up and function in all of these conditions.

To illustrate these points, we will look at four types of barriers and the issues related to their performance under normal and harsh conditions. Specifically, we will address exterior cladding, air barriers, moisture barriers, and fire barriers.

Enhanced Exterior Cladding

The first line of air and moisture defense on any exterior wall system is the outermost cladding material. Generically, any type of material can constitute cladding, ranging from masonry, stone, metal, wood, or composites. Its purpose is to provide the visible skin of opaque areas of the building and deflect wind, rain, sun, and heat. As such, it needs to be very durable to hold up over time and retain both its appearance and performance characteristics. Usually, this cladding layer is not considered to be air or water tight. Rather, it is intended to take the brunt of weather and sun exposure and protect the building materials and systems behind, while allowing for the management of air and water to drain away. While most cladding materials are up to the challenge, their useful life and need for maintenance will vary by material. Painted surfaces will need repainting, masonry and stone may need repointing, and applied coatings may need recoating. It is not surprising then that factory-finished metal or composite panel systems have become popular for cladding since they often require less maintenance, can be more durable over time, and are lighter weight than some other alternatives.

When thinking about cladding panels, it is common to think of the industry-standard flat panel installations. These may be appropriate for many situations, but their rigidity and ability to withstand high winds or other forces will be directly dependent on the inherent strength of the panel material. If the panel is surface applied directly to a substrate, that may help, but most are designed to be held away from the substrate, creating an intentional drainage space behind the cladding. In fact, the increasingly popular rainscreen systems are specifically designed to perform based on creating just such a space that anticipates water penetrating the cladding joints and being allowed to drain away harmlessly.

An alternative to flat panels is to use metal or aluminum composite material (ACM) panels in three-dimensional (3-D) panel shapes that easily install on building walls. The 3-D shape helps with the rigidity of the panel and avoids distortion or “oil canning” that can occur on some flat panels. Most, if not all, of these products have been independently tested for conformance with ASTM standards for structural load, water penetration, and air infiltration. The test results confirm that these external cladding systems can provide the rain, salt, and wind protection needed for buildings located in harsh environments. Manufacturers of 3-D panels provide a wide array of ACM product offerings, including convex or concave shapes, allowing architects and designers to work creatively.

The primary point of differentiation between fabricators of ACM panels is the attachment systems that each provide, usually made of aluminum or rigid PVC channels and clips. Some attachment systems are based on panels coming together in a butt-butt joint approach that is designed for interior installations but not for exterior facades. Others are based on a removable panel system that allows an ACM panel to be removed and a new panel installed into the same attachment clips, all in a matter of minutes. This can be very useful when sporadic, severe conditions are anticipated and replacements are needed in case of damage, vandalism, etc.

More sophisticated systems remove the need for routed returns on the panels by using the design of the panel and attachment system to join panels together securely. Such systems secure the panels to the building wall without the need for screws, rivets, or caulk. This means that the fabrication and installation process is radically simplified, reducing the overall cost of the installed system and shortening the lead time for getting the panels onto a building. Such systems can be enhanced with thermal break pads that can isolate the aluminum attachments from the building wall, effectively stopping the thermal transfer of energy through the cladding. The thermal break pads commonly available are made from a material called polyamide and are designed to easily affix to the aluminum attachment systems. Polyamide has been found to be very effective at stopping thermal transfer of energy between interior and exterior surfaces. This heat transfer control can be further enhanced using rigid insulation behind the cladding that is penetrated only with Z-channels or hat channels to secure the cladding in place. The combination of thermal break pads and continuous insulation helps provide high R-values for ACM panel installations.

Pablo M. Ipucha, Associate AIA, a senior project manager with Gene Kaufman Architect PC, has experienced the use of such a system, and here is what he has to say about it: “Incorporating ACM panels into a building envelope has benefited us in drastically reducing the width of the exterior wall, while meeting the R-value requirements. We were able to add 6 inches of usable real estate to the floor plans all around.”

Complete, Coordinated Air and Water Barrier Systems

Behind a cladding system, the rest of a wall assembly needs to be covered with air and water barriers. In some cases, that can be the same material; in others, it is two different products or materials. Generally, conventional wisdom suggests that the fewer the layers the better for simplicity and cost effectiveness. However, there are other considerations. First is the need for a complete, continuous barrier. That means it is not just about the material itself, but the means to attach it, the connections at seams or joints, and the treatment around penetrations, such as piping, wires, or sleeves. Just one small gap can lead to major problems from air and moisture infiltration, and those gaps can occur in a lot of different ways. The drawings and specifications, for example, may not be all encompassing enough to address different design details. On-site construction conditions might leave wide joints that are impossible to seal with a sealant. During occupancy, differential movement of materials can lead to joint failure. All of these situations need to be considered to achieve a truly durable and continuous system.

Second, the transitions of the barrier systems to other types of construction need to be taken into account. While the window-wall transition is where most problems occur, connections at roof to wall, foundation to wall, corners, penetrations, drift joints, and floor deflection joints are also critical connections with the potential for increased performance problems, not to mention professional liability. All of this underscores the need for continuous, compatible product systems that address all of the connections on the building envelope where most failures occur, especially under harsh conditions, such as thermal and seismic movement, hurricane forces, and blast resistance.

Continuous connections and transitions throughout the building envelope are key to the longevity of the structure and its structural components, energy consumption, indoor air quality, and maintenance. Specifications left to “others” for these connections lead to uncertainty, interpretation on the job, and trial and error. Traditional methods may not work, particularly over the long term after continual exposure to thermal or dynamic movement. Depending on the conditions, they may not even work at the outset if existing conditions leave unsupported gaps that cannot be addressed by sealants, foams, or peel-and-stick flashing membranes.

Fortunately, products are available from single-source manufacturers that are complete, coordinated, and effective. Some have created innovative, engineered solutions for critical connections that provide visible assurance of a secure, continuous seal without voids. For example, one system consists of pre-engineered, finished aluminum and silicone materials that are assembled and attached to a window or wall assembly. These assemblies provide a more secure and flexible option for sealing connections, notably improving air and moisture management at critical transitions. This type of solution also allows for greater movement and deflection beyond what sealants or self-adhered membranes can provide, particularly where dissimilar materials, such as curtain wall and various assemblies, connect—all while maintaining water and air tightness. The system’s design absorbs thermal movement and wind-loading stresses. The use of translucent, formed silicone gaskets allows the installer and/or inspector to see through the gasket to verify the recommended amount of sealant is properly applied, while ribs in the gasket ensure a minimum sealant thickness. This type of solution also addresses the problems with compatibility in the connection from the air barrier to the wall system. By using a compatible silicone sealant to serve as an adhesive and wet seal to an air and water barrier system, a turnkey solution can be specified and obtained. It should be required that the manufacturer submits proof that the complete system has been developed and tested for compatibility and long-term air and moisture protection.

Architects and others who seek to work with an air and water barrier company during design may be pleased to discover that some offer significant assistance related to the most successful ways to use their integrated systems. These companies are as interested as the design team is in mitigating risk by working to prevent barrier failures during construction or occupancy. Such design assistance may include a full review of the building enclosure system, suggestions for integrated product and connectivity solutions, and even project-specific 3-D CAD details with installation instructions. During construction, they can assist with mock-ups to document performance, quality assurance through preconstruction coordination, applicator training, plus inspection and on-site testing, if desired. In some cases, they can even assist with full building enclosure commissioning in addition to providing full-system performance warranties.

Appropriate Levels of Waterproofing

Some portions of a building need more than air and moisture protection—they need full waterproofing protection. This is true in low-slope roofing systems, but it can also be true in more severe conditions both above grade and below grade. Anywhere the potential exists for bulk water to collect or build up against a wall or floor system, then waterproofing is needed to protect it. There are, of course, multiple ways to achieve such waterproofing, and sometimes the choices can be confounding in terms of determining what is best for a particular project. Further, it is not always appropriate to assume that a standard solution that worked well for one building is appropriate for another.

One approach to determining the most appropriate solution is based on a concept called “redundant field-fabricated composite design,” which is the integration of multiple waterproofing types into one organized system. This concept allows architects and designers to customize the system, protecting their structure based upon the site conditions, performance expectations, and budget considerations of the project team. It also allows for an assessment of the severity of the waterproofing needs and allows for a system to be selected based on that need. Essentially, the approach is to be sure that the products and system used will keep building structures dry and safe, but to use the appropriate level of protection needed—not overdue it unnecessarily, nor come up short on meeting the true waterproofing need.

Some manufacturers recognize this approach to waterproofing and have made it easier to understand the differences between different layers or types of protection using their commercial waterproofing products. Essentially, they provide a “good, better, best” approach to waterproof protection through different system configurations that are suitable to protect below-grade foundations and exposed decks. Such field-installed composite waterproofing systems are defined by multiple layers. The first layer is a spray fluid-applied membrane that covers concrete or masonry. Commonly, this is a water-based polymer modified asphalt (PMA) membrane. The second layer is a reinforcing fabric commonly made from polyester to take up any undue stresses from movement. An additional layer can be specified that allows for some added thickness to absorb and drain water away. This layer is commonly made of bentonite or a similar water absorbing and draining material. The final outer layer protects the drainage medium as well as the primary membrane. Such outer layers can be a composite made up of a high-density polyethylene (HDPE) core and nonwoven polypropylene fabric drainage or a polypropylene core and polypropylene fabric.

The goal of this holistic approach to waterproofing is to create a series of barriers, drainage channels, and reinforcing protection over a concrete or masonry wall, slab on grade, or other structure. Each of these layers can be specified or selected based on the particular needs of the project with properties that suit the harshness of the building site or the degree of protection required. By working with one manufacturer that provides a complete system with the multiple choices, the design can be simplified and the performance maximized. At least one manufacturer provides such a system that truly combines all types of waterproofing into one coordinated system.

In addition to the actual system, it is important to understand how the edges of these systems are detailed. On vertical or sloped walls, a continuous metal termination strip across the top of a hybrid membrane allows for the transition between the area above and below the waterproofed area, but it also holds the drainage barrier in place. The bottom needs to account for the footing condition and allow the vertical drainage to be picked up, channeled, and moved away from the wall. That may mean adding some products specifically designed to be compatible with the rest of the waterproofing system that can be integrated as a horizontal or sloped drainage medium. Finally, the collected water must be able to drain away from the wall altogether either through drain tiles or piping or through the use of backfill materials that will allow for water dispersion.

Horizontal conditions, such as concrete floor slabs on grade, can be equally demanding, particularly if the groundwater level is high or the soil around and under the slab becomes saturated due to heavy rains. In order to prevent water infiltration, the waterproofing system needs to be continuous under the floor slab and connect with the wall edges to form a continuous barrier to drain and stop the water. This need can be exacerbated if freezing conditions are encountered near the building or if seismic activity is prevalent. In these cases, the waterproofing membrane system is subject to additional stresses and pressures beyond the normal hydrostatic concerns. Hybrid or composite systems that incorporate the multiple attributes of membrane, reinforcing, drainage, and protection into one coordinated system are most likely to perform well under these conditions compared to less complete or less coordinated approaches from multiple manufacturers.

Overall, hybrid, composite waterproofing systems leverage the attributes of multiple waterproofing technologies into a coordinated system. This enables building owners to receive a better overall value by receiving the appropriate level of protection, provided the architect selects the best mix of products and barriers to do the job efficiently. Further, by combining and leveraging the benefits of each waterproofing component, installation times can be decreased while overall protection increases compared to other types of waterproofing systems.

Keeping the Fire Barriers Uninterrupted

Fire separations are required in buildings for good reasons—there are too many tragic examples of preventable death and injury from fire and smoke in buildings. While a common reaction is to require fire sprinklers as an “active” means of fire safety, architects are well aware of the “passive” approach of using compartmentalized spaces that are enclosed on all horizontal and vertical sides with fire-rated construction. As in all barrier systems, the main body of the barrier is fairly well understood—in this case, noncombustible construction using protected steel, concrete, or gypsum board. The issue becomes addressing the seams or joints in this construction. In particular, large buildings require expansion joints that are often located in fire-rated construction that separates occupied spaces from each other, from vertical shaft ways, or from adjacent tenancies. The apparent paradox of providing an intentional break in the structure to allow for normal expansion and contraction while still maintaining a fire rating is addressed by providing an expansion joint fire barrier.

There are three common types of fire barrier expansion joint systems, and the suitability of each will depend on the size of the joint or gap as well as the conditions that the joints are subjected to.

• Compression systems are typically for 4-inch and smaller expansion gap widths. These products are commonly comprised of mineral wool strips held in place through compression. These are topped with fire caulk sealant to secure the barrier in place and protect from water infiltration. Fire lab testing of compression systems is typically done for both concrete and drywall conditions.
• Fire-rated foams are suitable for 6-inch and smaller gaps and conditions where abuse is not likely. These systems are comprised of open-cell polyurethane foam impregnated with a fire-retardant material. These foams can be faced with colored silicone to match a desired décor or design aesthetic. Foams can also provide acoustic and insulation properties. Fire-rated foams are usually lab tested in concrete and cement-board wall conditions (not drywall).
• Fire blankets are the most versatile systems, suitable for expansion joint gaps of 2 to 32 inches and able to withstand high rates of movement. Fire blanket systems come in two forms—either ceramic cloths with intumescent layering or graphite sheet goods encasing insulating blankets. In seismic conditions, they allow for approximately 50 percent of joint compression and expansion movement. Some models are able to retain their rating throughout lateral shear movement testing, while others cannot. Fire blankets are tested in concrete, but alternate substrate conditions may also be acceptable.

In all cases, the continuous, uninterrupted installation of the fire barrier is critical for life safety. This is especially true when using fire blankets since they need to be fully and carefully connected to the adjacent concrete surfaces and form a continuous barrier where vertical and horizontal conditions meet. At least one manufacturer has addressed this concern through the use of a modular system that allows separate sections to nest together creating tight, continuous protection. Further, the edges of the blanket are pre-attached to metal flanges, assuring that the proper seal is obtained instead of relying on field installation to create an uncertain seal. These pre-attached flanges drastically reduce labor costs and ensure a uniform installation for a more reliably continuous seal.

Fire blankets can be specified either to withstand water or not. Those that cannot withstand water exposure and become wet are often rendered useless against smoke, fire, and heat, and even after re-drying carry diminished fire resistance. Products that are rated and tested for water exposure during or after construction or for open structures, such as parking facilities and stadiums, provide fire protection even if they become wet. It is important then to select and specify the appropriate material for the water conditions anticipated in the building.

Conclusion

Barriers of multiple types are needed in buildings to protect not only the building but the people inside. In all cases, the continuity and integrity of those barriers are critical to their performance. This is compounded by the fact that different conditions ranging from moderate to harsh will impact the ability of the barriers to perform as intended. Architects and designers who understand the range of options and the suitability of those options to different conditions can design and specify buildings that are safe, durable, and sustainable over the long run.

Peter J. Arsenault, FAIA, NCARB, LEED AP, is a practicing architect, sustainable building consultant, continuing education presenter, and prolific author engaged nationwide in advancing better building performance through design. www.linkedin.com/in/pjaarch