Tag Archives: air barrier

Much to Think About with Cavity Walls

slaton patterson sutterlinFAILURES
Deborah Slaton, David S. Patterson, AIA, and Jeffrey N. Sutterlin, PE

In response to greater focus on building envelope energy performance, insulation use in the exterior wall cavity has increased. For all U.S. climate zones, the 2012 International Energy Conservation Code (IECC) requires continuous insulation (ci), which is defined by the American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE) as “insulation that is continuous across all structural members without thermal bridges other than fasteners and service openings.” In cavity wall construction, this is typically accomplished with a continuous plane of rigid or semi-rigid insulation outboard the water (or weather)-resistive barrier/air-vapor barrier (WRB/AVB).

Foam plastics (e.g. extruded polystyrene [XPS]) and semi-rigid mineral wool insulation have been the most commonly used in exterior wall cavities for this purpose. Each has certain advantages and disadvantages. For example, XPS has a slightly higher R-value (nominally 5.0 per inch) as compared to mineral wool (nominally 4.2 per inch), but is considered combustible while mineral wool is not. Use of foam plastic insulation within the exterior wall cavity of Type I to IV construction triggers the need for testing per National Fire Protection Association (NFPA) 285, Standard Fire Test Method for Evaluation of Fire Propagation Characteristics of Exterior Non-load-bearing Wall Assemblies Containing Combustible Components.

In the 2012 International Building Code (IBC), Section 1403.5 also requires combustible WRBs in the exterior wall assembly of buildings greater than 12 m (40 ft) in height comply with NFPA 285 testing of the assembly. The 2015 IBC appears to have recognized the burden this requirement has placed on the construction industry; NFPA 285 testing is no longer required when the WRBs are the only combustible material present, and are covered with non-combustible claddings like brick, terra cotta, concrete, or metal.

High-density closed-cell foam plastic insulations can function as air barriers and Class 2 vapor retarders. However, when improperly detailed or installed, they can retard the drying of moisture that enters the wall assembly and collects against the WRB/AVB. Thus, care must be taken to detail and install the insulation to minimize the passing of bulk water inboard of its exterior face.

Mineral wool insulation, while typically free-draining, can retain moisture and wet the WRB/AVB until the moisture drains through or evaporates. Some mineral wool insulation products are manufactured with enhanced water-resistance, making them more suitable for use in an exterior wall cavity or rainscreen application. No matter which insulation is used, the wall cavity should be designed with sufficient ventilation provisions to allow materials within to dry out.

WRB/AVBs used inboard of the insulation have evolved to include fluid-applied products, which have different properties than traditional sheet barriers. Recognizing the potential for moisture or bulk water that enters the wall cavity to be held against the WRB/AVB by the insulation, the designer must understand the limitations of all products involved in the installation to avoid the failure shown in the photo below.

Moisture collecting on the horizontal surface likely contributed to the failure of this fluid-applied water-resistive barrier/air-vapor barrier (WRB/AVB). Photo courtesy Jeffrey N. Sutterlin

Moisture collecting on the horizontal surface likely contributed to the failure of this fluid-applied water-resistive barrier/air-vapor barrier (WRB/AVB). Photo courtesy Jeffrey N. Sutterlin

The opinions expressed in Failures are based on the authors’ experiences and do not necessarily reflect those of the CSI or The Construction Specifier.

Deborah Slaton is an architectural conservator and principal with Wiss, Janney, Elstner Associates, Inc. (WJE) in Northbrook, Illinois, specializing in historic preservation and materials conservation. She can be reached at dslaton@wje.com.
David S. Patterson, AIA, is an architect and senior principal with WJE’s Princeton, New Jersey, office, specializing in investigation and repair of the building envelope. He can be e-mailed at dpatterson@wje.com.
Jeffrey N. Sutterlin is an architectural engineer and senior associate with WJE’s Princeton office, specializing in investigation and repair of the building envelope. He can be contacted via e-mail at jsutterlin@wje.com.

Using Temperature to Control Condensation in Cold Climates

Photo © BigStockPhoto/Pavel Losevsky

Photo © BigStockPhoto/Pavel Losevsky

by Daniel Tempas

Designers have been concerned about condensation in walls for decades. Since the mid-1970s, the greater amounts of insulation specified in the building envelope has increased the likelihood for condensation somewhere in the assembly. Many articles have been written over the years describing the physics of the problem and, for the vast majority of the time, there has been a laser-like focus on one solution.

Initially, water vapor diffusion was seen as the likely culprit for condensation problems and designers and consultants spent hours running and analyzing wall assemblies using the ‘profile’ (or ‘dewpoint’) method (Figure 1). With such analyses came the concept the wall system should be tuned for maximum condensation resistance by altering or selecting the appropriate permeability of the wall components.

The rule of thumb became to place low-permeability materials/retarders on the wall’s warm side, and higher permeability materials on the cold side (Figure 2). In this fashion, the designer strove to make it difficult for water vapor to enter the wall (lessening water’s ability to condense in the wall) and easy for water vapor to leave the wall (drying out any water that still managed to get inside). Manufacturers began to introduce high-permeability air barriers, water barriers, and sheathings along with ‘smart’ vapor retarders for the warm side of the wall.

This low-perm/high-perm strategy reveals two goals in wall design: the efforts to decrease condensation potential and increase drying potential. Reducing condensation potential is fairly well-understood but increasing drying potential is a less commonly sought after goal. Both are important for robust wall design.

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Problems with permeability
While all this sounds good, it was not necessarily preventing condensation problems. There are some basic facts about permeability designers need to understand to get a better grasp on not only controlling condensation, but general wall design.

Fact 1: If a material’s temperature gets low enough, water vapor will condense on or in it, regardless of how high its permeability.
This is something to keep in mind in cold climates. This author has seen both fiberglass batts and high-perm air barriers with ice encrusted on their surfaces. When a material gets cold, its effective permeability dramatically drops. High permeability is useless at low temperatures. In other words, condensation is a temperature-related phenomenon.

Fact 2: Cold water dries slower than warm water, no matter how permeable the shell surrounding it.
Increasing a wall assembly’s drying potential is an important and valuable goal. However, water at lower temperatures will take a long time to dry because the related evaporation rate is slow. Simply put, robust drying potential cannot be achieved in the layers of a wall assembly that are at low temperatures.

For example, one can consider a puddle on a sidewalk (Figure 3). How long does it take that puddle to dry? If the ambient temperature is 32 C (90 F), it will not take long at all, perhaps only several minutes. However, when the ambient temperature is only 4 C (40 F), the puddle might take hours or even days to evaporate. This is an example of the profound effect temperature has on evaporation rate.

Fact 3: Air movement transports far more water vapor than diffusion.
This is something that has been understood by building scientists for quite some time, and has been filtering into the design community for decades. However, the subtle ramifications of this knowledge are just now finding their way into the world at large. The fact air movement is so dominant in water vapor transport (and subsequent condensation) means any vapor retarder must work either as, or in conjunction with, a near perfect air barrier.

Any installation flaw or penetration in the air/vapor barrier on the higher temperature side will result in an amount of air leakage that will overwhelm any planned benefit from that barrier’s diffusion characteristics. This will result in a much greater potential for condensation in or on any layer that is at a low enough temperature for condensation to occur. Additionally, this means diffusion-based analyses of the wall system are rendered moot.

Fact 4: Water vapor does not move from areas of higher temperature to lower temperature.
Thinking this is the only direction water vapor flows is incorrect. Water vapor moves from areas of high concentration to low concentration, regardless of the direction of heat flow. This is an important concept when it comes to understanding drying verses condensation.

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Temperature to the rescue
After considering these four facts regarding water physics, it would seem there is a great deal of confusion and trouble regarding wall design. The manipulation of material water vapor permeabilities in a wall design cannot achieve a truly robust assembly. What can be done?

‘Temperature’ is the common thread running through the facts regarding water vapor condensation in wall assemblies. A wall assembly’s temperature profile plays a critical role in the ability to resist condensation and promote drying. This is not an unknown concept, of course—a quick search of building science literature will yield the occasional article mentioning the importance of the temperature profile. The problem is temperature profile manipulation is far down the list of the wall designer’s methods for creating a more robust wall. It is seen as unimportant when in reality, it is the opposite.

As much of the wall insulation as possible should be placed on the outbound side of the assembly (Figure 3). This is easy to do whether the base wall is metal stud, concrete masonry unit (CMU), or poured concrete. In cold-weather conditions, this will warm the entire interior wall, changing the temperature profile with far-reaching consequences (Figure 4).

For example, designing a wall assembly so more of the components will be in the higher temperature portion of the wall profile significantly reduces the potential for condensation. Not every part of a wall is equally sensitive to exposure to moisture. A standard rainscreen veneer wall assembly (Figure 5) is not sensitive to water, as it must be exposed to the elements on a constant basis. The support elements for the veneer are also not sensitive to water—they are in the drainage space behind the veneer and quite a bit of water reaches that space. As for the insulation layer on which the supports rest, it too must be moisture-resistant for the same reason. If condensation can be forced to happen only around components immune to water, then the wall design is completely robust in its resistance.

Designing a wall assembly so more of the components will be in the higher temperature portion of the wall temperature profile also significantly increases the drying potential for any water that does find its way into the wall. Referring back to the puddle example, higher temperatures means much higher drying rates. Combine the greater drying temperature with the longer drying time and one has a wall with a drying potential increased by an order of magnitude or more.

The importance of temperature modification to improve walls systems can be better understood when considering that both condensation and drying are two-step processes (Figure 6):

  • movement of water vapor to or from the point of condensation or drying; and
  • actual phase change of water from the vapor phase to the liquid phase (condensation), or vice versa (drying).

No matter how rapidly water vapor is transported to a given location in a wall assembly, either by the slow process of diffusion or the rapid process of air infiltration, condensation will not take place if the temperature of that location is high enough. This is also true in the drying process. No matter how easy it is for water vapor to exit a given location in a wall assembly, either by the slow process of diffusion or the rapid process of air infiltration, drying will not take place when the temperature of that location is too low. Again, temperature plays a critical role in the condensation and drying processes in a wall assembly. Altering the temperature profile of a wall assembly through judicious placement of materials is an effective method to control these processes.

The aforementioned Fact 4 about the true nature of the movement of water vapor makes it clear even when the exterior sheathing/insulation is completely impermeable, the drying potential of this wall is much greater than the previous design and the condensation potential is much lower. Since it is at a temperature near to that of the interior, any water in the stud cavity will have a much higher evaporation rate, which means a much higher drying rate. Also, it will easily dry to the building interior.

Proper placement of the right insulation negates the need for a vapor retarder. Why worry about water vapor getting into the wall when most of it is at a temperature far too high for condensation to take place? If the insulation has been well-chosen, any condensation taking place toward the exterior of the building will be minute and meaningless. Besides, the stud cavity needs to dry to the interior, and an interior vapor retarder will only get in the way.

The overall robustness one gains from placing most wall components in the highest temperature part of the temperature profile overwhelms almost every other condensation/drying consideration in the wall design.

Using the temperature profile of a wall as part of the design process leads to a wall that is easier to build. Relying on permeability (to alter water vapor diffusion rates) in the design process for a wall assembly results in a dependency not only on material properties, but also on the quality of installation.

A critical part of any vapor retarder (or air barrier) is its continuity. Any flaw in the installation process of that air/vapor retarder that results in breaches of its continuity heavily compromises its ability to reduce condensation potential. This would include unrepaired construction damage or poorly sealed seams. Even normal penetrations in the wall assembly, like outlets and switches, present opportunities for discontinuity in the air barrier/vapor retarder.

On the other hand, manipulation of the temperature profile of a wall assembly is only about positioning the right amount of insulation in the right location in the wall. A board of insulation is far more robust that film of plastic, making insulation continuity far easier to achieve. Also, the outside of the wall typically has far fewer penetrations, making them far easier to handle.

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Conclusion
Designing wall assemblies by adding or altering the permeabilities of the wall components is an artifact of the limited analysis tools relying on investigation of water vapor movement via diffusion. Such walls gain only mild improvements in condensation resistance and, more importantly, drying potential. To create a truly robust wall system with the greatest condensation resistance and drying potential, designers must look at altering the temperature profile of the wall assembly by moving insulation as far as possible to the wall’s exterior.

This does not mean one should no longer think about, or design with, the permeability of materials in mind, of course. Rather, it means the water permeability analysis/profile part of design efforts should be relegated to the proper place in the design consideration hierarchy: behind the wall temperature profile design effort.

Daniel Tempas is a building envelope technical service representative for Dow Building Solutions; he has held technical and engineering positions at the Dow Chemical Company for almost 30 years. Tempas is a (HERS) rater, a Leadership in Energy and Environmental Design (LEED) Green Associate, and a member of the RESNET Training Committee. He has also been a member of ASTM, Exterior Insulation and Finishing Systems Industry Members Association (EIMA), and Building Thermal Envelope Coordinating Council (BTECC). Tempas can be reached atdtemp@dow.com.

Wind Load and Air Barrier Performance Levels

Photo courtesy DuPont Building Knowledge Center

Photo courtesy DuPont Building Knowledge Center

by Maria Spinu, PhD, LEED AP, Ben Meyer, RA, LEED AP, and Andrew Miles

Continuous air barriers have become mandatory for the building envelope, with energy codes recognizing the importance of air leakage control. However, simple inclusion of an air barrier requirement does not guarantee the desired performance in the field. These systems must be properly installed, meet the building envelope structural wind loads, and maintain their function over time.

There are two accepted performance levels for commercial air barrier systems, determined by the structural design parameters for the building envelope:

  • ASTM E1677, Standard Specification for Air Barrier Material or System for Low-rise Framed Building Walls, applicable to envelope design specifications of up to 105-km/h (65-mph) equivalent structural loads; and
  • ASTM 2357, Standard Test Method for Determining Air Leakage of Air Barrier Assemblies, for buildings designed to withstand structural loads beyond that level.

This article describes the air barrier performance requirements for the desired wind load design specifications. The performance level is not determined by the type of air barrier material, but by the installation details. Examples of how these details can impact the performance level for a given air barrier system will be provided, with special emphasis on mechanically fastened air barriers.

Summary comparison between ASTM E1677 and ASTM E2357 wall assembly testing.

Summary comparison between ASTM E1677 and ASTM E2357 wall assembly testing.

Air leakage control and air barrier materials
Air leakage control is achieved through a continuous air barrier. Any material with an air permeance less than 0.02 L/(s • m2) @ 75 Pa pressure differential (0.004 cfm/sf @ 0.3 in. w.c. or 1.56 psf pressure differential), when tested in accordance with ASTM E 2178, Standard Test Method for Air Permeance of Building Materials, qualifies as an air barrier. Even though many common building products are air barrier materials (e.g. metal sheets, glass, oriented strandboard [OSB], and gypsum board), a continuous air barrier requires many compatible components to achieve a plane of airtightness. In practice, most air barrier materials are specifically designed membranes effectively integrated into a continuous air barrier system.

Testing of walls with mechanically fastened air barrier systems. Image courtesy DuPont and ATICommon air barrier materials include mechanically fastened (i.e. building wraps), fluid-applied, and self-adhered membranes. The choice depends on many factors, such as the substrate, desired performance level, installed cost, personal preference, local practices, and regional availability.

For example, in framed construction where air barriers are applied over exterior sheathing, building wraps are the most cost-effective. For masonry or concrete backup walls, fluid-applied membranes are the common choice. Self-adhered membranes can be used with either substrate, but most are vapor-impermeable and their use should be limited to specific climates and wall design options.

In the case of vapor-impermeable air barriers, the membrane plays a dual role: air and vapor barrier. While air barriers could be installed anywhere in the building envelope, vapor barrier location and use is climate- and design-specific. For example, vapor barriers are required only in cold climates, and must be installed at the ‘warm in winter’ side of the envelope. In warm-humid climates, a vapor barrier could still be acceptable to the outside of the envelope (where the air barrier is generally installed) when design options for drying pathways are available—such as when vapor-permeable materials must be used at least in one direction (in this example, everything to the inboard from vapor barrier must be vapor-permeable). Exulation wall design (i.e. exterior insulation only, no insulation in the stud cavity) can also use vapor-impermeable air barriers. Building physics must always be considered when an unintended vapor barrier is used in a wall assembly.

There are four essential performance requirements for air barriers:

  • air infiltration resistance;
  • continuity;
  • structural integrity; and
  • durability.1

Another critical property is vapor permeability, which could impact moisture management in wall assemblies. However, the codes do not specify the air barriers’ vapor permeance—the decision is left to the building envelope designer.2

CS_July_2014.inddAir infiltration resistance is an inherent material property for air barrier materials. Other requirements depend not only on material properties, but also on the performance of the installed system determined by the integration of air barrier components into a continuous system, as well as the durability under use conditions. In addition to the primary air barrier membrane, an air barrier system includes installation and continuity accessories, such as primers, mechanical fasteners, seam tapes, flashing, adhesives, and sealants.

This article mainly focuses on structural integrity requirement, which is the ability of an air barrier system to withstand wind loads experienced during the building’s use after construction is complete. There are two accepted performance levels based on building envelope design parameters with regard to wind loads and wind-driven rain. To establish the performance level of an installed air barrier system, air barrier wall assemblies must be tested in accordance with the respective ASTM standards.

Installed air barrier performance and wall assembly testing
Testing is essential for demonstrating performance of installed air barrier assemblies. This process is critical for developing robust installation guidelines for achieving air barrier performance levels consistent with structural design specifications.

As mentioned, ASTM E1677-11 applies to air barrier performance levels for building envelope design requiring up to 105-km/h (65-mph) equivalent structural loads, and up to 24-km/h (15-mph) equivalent wind-driven rain water infiltration resistance. This level is generally adequate for buildings of up to four or five stories, but higher performance is typically required on some low-rise structures like medical facilities and military buildings. ASTM E2357-11, on the other hand, applies to air barrier performance levels for building envelope design structural loads beyond this—such a performance level is generally necessary for buildings taller than five stories.

CS_July_2014.inddBoth test methods are performed on 2.4 x 2.4-m (8 x 8-ft) wall assemblies. ASTM E1677 requires testing of a single, opaque wall assembly (i.e. no penetrations except for the fasteners), while ASTM E2357 involves two specimen—an opaque wall and a penetrated wall that includes standard penetrations such as window openings, external junction boxes, and galvanized duct.

Both test methods require pressurization and depressurization testing, but use different pressure loads and schedules. The major differences between the two test methods are summarized in Figure 1, and consist of the pressure loads, schedule, and requirement for water infiltration resistance testing.

As shown, ASTM E1677 requires five test pressures:

  • ± 75-Pa pressure differential (1.56 psf, 25 mph);
  • two pressures below 75 Pa; and
  • two pressures above 75 Pa.
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Examples of window flashing for ASTM E2357 performance level.

The pressure loading schedule includes sustained loads of up to ±500 Pa (10.4 psf, 65 mph). This standard requires testing for water infiltration resistance per ASTM E331, Standard Test Method for Water Penetration of Exterior Windows, Skylights, Doors, and Curtain Walls by Uniform Static Air Pressure Difference. Air barriers or air retarders (as they are referred to in ASTM E 331) are classified as either Type I or Type II. Type I air barriers, which can also perform as water-resistive barriers (WRBs), must exhibit no water penetration when tested at 27 Pa (11 in. water pressure difference)—equivalent wind speed of approximately 24 km/h (15 mph)—during a 15-minute test period. Type II air barriers are not required to be tested in accordance with ASTM E 331.

ASTM E2357 requires a minimum of seven test pressures, from ±25 Pa (0.56 psf, 15 mph) to ±300 Pa (6.24 psf, 50 mph). The pressure loading schedule includes sustained, cyclic, and gust winds up to ±160-km/h (100-mph) equivalent wind speed. This standard does not require ASTM E331 testing for water infiltration resistance, which is a significant limitation since many air barriers are commonly required to also perform the WRB function and are exposed to pressure loads above 105-km/h (65-mph) wind.3

A building wrap air and water barrier system is installed over the exterior sheathing, prior to the installation of metal panels. Proper installation is critical for meeting the building envelope structural wind loads and maintaining the air barrier continuity over time.

A building wrap air and water barrier system is installed over the exterior sheathing, prior to the installation of metal panels. Proper installation is critical for meeting the building envelope structural wind loads and maintaining the air barrier continuity over time.

Air leakage results are reported at 75 Pa for both methods. Current codes require the average air leakage rate for air barrier assemblies must not exceed 0.2 L/(s•m2) @ 75 Pa pressure differential (0.04 cfm/sf under a pressure differential of 0.3 in. w.g. or 1.57 psf) when tested in accordance with ASTM E2357 or ASTM E1677.

Since a continuous air barrier experiences both positive and negative pressures during its use, it is important assemblies be tested under both positive and negative pressures. The negative load (under suction) is typically the most severe, as it tries to pull the air barrier off the wall. Different air barrier types have different susceptibility to negative pressure loads.4

For fluid-applied air barriers, wind loads are transferred to the substrate underneath. When the substrate is masonry or concrete, a fully adhered fluid-applied air barrier has excellent structural performance under suction, as the pressure it typically takes to separate it from the substrate far exceeds the actual pressure it must withstand.

However, for framed wall construction, the structural performance of fully adhered fluid-applied air barriers under negative wind loads depends on how well the sheathing is fastened to the building structure. When the exterior sheathing is not installed to withstand the design wind loads, this could reduce the air barrier system’s structural performance. In this case, the typical mode of failure for fluid-applied air barrier is the sheathing pulling over the screws.

CS_July_2014.inddIn comparison, when building wraps are installed over exterior sheathing, the air barrier membrane is supporting the entire load. Consequently, this type of air barrier is more susceptible to wind. The suction forces are transferred through the air barrier membrane to the mechanical fasteners, and then back to the structural supports (i.e. steel or wood studs). As a result, for a mechanically fastened air barrier, the wind load performance is determined by the type of fasteners and the fastener schedule.

The photos in Figure 2 show an example of high-pressure performance testing of commercial building wraps and exemplify the extreme forces experienced by the air barrier wall assemblies under negative pressure loads. The steel studs actually buckle under the pressure differentials used for high performance testing of building wraps (left), but a properly fastened building wrap withstands this pressure and maintains the system’s structural integrity (right).5

These pictures demonstrate the importance of proper fastening of building wraps to withstand high suction loads and maintain the air barrier structural integrity during use. A common mistake with building wraps installation is use of staples for fastening the building wrap into the exterior sheathing (a practice often employed for WRBs in residential construction), rather than employing recommended screws with washers to fasten the membrane into the structural members (wood or steel studs).

Building wrap manufacturers usually provide guidelines on the type of fasteners and the fastening schedule recommended for meeting the desired performance level. Figure 3 provides an example of fastening type and schedule guidelines and the maximum wind loads allowable.

Alternate fasteners are also allowed, when applicable. Examples include standard brick tie base plates and metal plates, metal channels, horizontal z-girts, and wood furring strips mounted vertically. They can be used in conjunction with the manufacturer-recommended fasteners to meet and/or satisfy the desired design performance.

In addition to fastener selection and spacing, other installation details are critical when designing for a specific performance level. Some building wrap manufacturers provide different installation details for ASTM E1677 and ASTM E2357. These include details on sealing of penetrations, transitions, and interfaces. For example, no additional fastener sealing is necessary for building envelope design requiring up to 105-km/h (65-mph) equivalent structural loads (i.e. ASTM E1677), when recommended fasteners and schedules are used. However, if higher air infiltration resistance is desired (i.e. ASTM E2357), self-adhered flashing must be used under the fasteners.

Figure 4 shows examples of alternate fasteners, as well as the use of self-adhered flashing under the fasteners for ASTM E2357 performance level. The same recommendations are also for fluid-applied membrane fasteners.

A mechanically-fastened air and water barrier system is installed over the exterior sheathing. Fluid applied air barrier was also used for concrete masonry unit (CMU) portions of this project (not visible in the picture). Proper integration between the two air barriers used for CMU and gypsum-covered metal stud walls was critical for continuity and structural integrity.

A mechanically-fastened air and water barrier system is installed over the exterior sheathing. Fluid applied air barrier was also used for  concrete masonry unit (CMU) portions of this
project (not visible in the picture). Proper integration between the two air barriers used for
CMU and gypsum-covered metal stud walls was critical for continuity and structural integrity.

Among the most critical details determining the air barrier structural performance level are windows and doors integration into the continuous system. Most manufacturers provide step-by-step window installation guidelines. Changes in the provider’s detailing and sequencing could change the performance level (i.e. ASTM E1677 or ASTM E2357). Figures 5 and 6 show examples of specific details for achieving the desired wind load design specifications.

The detail in Figure 5 shows how the window rough openings are treated with self-adhered flashing, for the high-performance level required by ASTM E2357. For example, when the building has non-flanged, storefront, and/or curtain wall windows, the air barrier membrane is typically cut flush with the edge or the rough opening. Then, the self-adhered flashing is installed to protect the rough opening and provide a positive termination of the air barrier membrane. The pictures on the right show examples of high-performance flashing for non-flanged and/or curtain wall windows that may be bumped out from the wall plane.

Figure 6 shows an example of window flashing for ASTM E1677 performance level. The picture captures the alternate head detail, which is generally allowed for building structures with building envelope design requirements not exceeding ASTM E1677. After the air and water barrier is wrapped into the window rough opening, a top hat is created with sealant to divert water away from the window opening (if the air barrier is also intended to serve as the WRB). WRB cut pieces are then installed (I) by wrapping in and around the studs at the jamb and the head, and stapling to inside framing to secure (A). The next steps include (II): (A) apply a continuous sealant bead along jambs and head, (B) install flanged window, (C) install jamb flashing, and (D) install head flashing.

A properly installed building wrap air and water barrier system is the most cost-effective option for this building with sheathing substrate and multi-story curtain wall consisting of brick and solid-surface cladding panels.

A properly installed building wrap air and water barrier system is the most cost-effective
option for this building with sheathing substrate and multi-story curtain wall consisting
of brick and solid-surface cladding panels.

The recommended installation guidelines are based on many wall assembly tests, and changing the installation details in the field could affect the performance level for the installed air barrier assembly. Engaging the air barrier manufacturers in early design stages is critical to understanding the installation details requirement and the optimal installation sequence to achieve the desired performance level. Additionally, it helps avoid unnecessary delays during the construction phase.

The difference between the two performance levels for air barriers is not always understood by industry professionals and installers, and not clearly stated by codes. For example, American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE) 90.1-2013, Energy Standard for Buildings Except Low-rise Residential Buildings, Section 5.4.3.1.3.b, defines code-compliant air barrier assemblies as:

Assemblies of materials and components (sealants, tapes, etc.) that have an average air leakage not to exceed 0.04 cfm/sf under a pressure differential of 0.3 in. w.g. (1.57 psf) when tested in accordance with ASTME 2357, ASTM E1677.

As evident from this article, performance levels for ASTM E1677 and ASTM E2357 are not equivalent—nevertheless, ASHRAE 90.1-2013 provides the two options as equals. It is little wonder there is confusion in the industry, and the potential impact of changes to the manufacturer’s installation guidelines is not always appreciated.

A building wrap air and water barrier system is installed over the exterior sheathing, exterior insulation is installed over the air barrier, and exterior cladding (brick, metal panels, and solid surfacing) are installed to the outside.

A building wrap air and water barrier system is installed over the exterior sheathing, exterior insulation is installed over the air barrier, and exterior cladding (brick, metal panels, and solid surfacing) are installed to the outside.

Fortunately, Air Barrier Association of America (ABAA) recently introduced an evaluation process for air barriers, in order to apply consistent standards across the industry. On its website, the group lists the air barriers that have been evaluated and demonstrated to meet ASTM E2357 performance level. (For more, see “ABAA-evaluated Air Barrier Assemblies.”)

Current limitations of air barrier standards
Code requirements on air leakage control have led to a large increase in the number of materials claiming to perform as air barriers. The challenge with some airtight materials is in achieving a continuous and durable air barrier system. For example, many materials designed to perform other functions (e.g. thermal insulation or exterior sheathing) that are also resistant to air infiltration have been promoted as air barriers. While such products are adequate air barrier ‘materials,’ the long term continuity and durability of these air barriers as ‘systems’ is still an open question.

Some such materials have passed the current air infiltration resistance requirements for ‘as-installed’ air barrier assemblies per ASTM E2357 and are listed at the ABAA website. However, these systems may fall short of long-term durability under the use conditions. Additional testing, such as thermal cycling and water resistance, would be necessary to assess the long-term durability of these systems. This discussion is beyond the scope of this paper, but it should be of concern to the industry.

Conclusion
Building energy codes mandate a continuous air barrier for leakage control. The air barrier system must withstand the conditions a building is exposed to during its use. There are two acceptable performance levels for air barrier wall assemblies—ASTM E1677 and ASTM E2357—that are determined by the structural design parameters for the building envelope. Some air barrier manufacturers have developed two-tier installation guidelines for the desired level, and altering the guidelines could change the performance.

A fl uid-applied air and water barrier system is ideal for this building, which consists of multiple substrates and exterior claddings. The air barrier was installed over CMUs and gypsum board sheathing substrates; the multi-story curtain wall consisted of cut limestone on the fi rst fl oor, brick veneer on the upper fl oors, cast stone trim work, and perforated metal panels.

A fluid-applied air and water barrier system is ideal for this building, which consists of multiple substrates and exterior claddings. The air barrier was installed over CMUs and gypsum board sheathing substrates; the multi-story curtain wall consisted of cut limestone on the first floor, brick veneer on the upper floors, cast stone trim work, and perforated metal panels.

A major limitation of ASTM E2357 is the lack of water infiltration resistance requirement. Very few manufacturers integrate testing for ASTM E2357 air infiltration resistance with ASTM E331 water infiltration resistance of installed wall assemblies.

Current test methods are effective in measuring performance of newly installed air barrier assemblies under pressure differentials experienced by above-grade exterior walls and represent a huge step forward from relying solely on materials properties. However, current standards do not provide information about the long-term performance under field use conditions experienced by the buildings, which include seasonal and daily temperature variations.

The air barrier system performance is only as good as the weakest link, and differential expansion and contraction of multicomponent air barrier systems can compromise its continuity. Integration of rigorous structural integrity testing of air barrier wall assemblies with thermal cycling and water infiltration resistance will provide valuable information on the long-term durability of these systems.

Notes
1 These requirements have been described in various articles, including 2006’s “Air Barriers: Walls Meet Roofs,” by Wagdy Anis and William Waterston (www.shepleybulfinch.com/pdf/Air_Barriers_wall_meets_roof_final.pdf) and 2004’s “Air Barriers, Research Report,” by Joseph Lstiburek (www.buildingscience.com/documents/reports/rr-0403-air-barriers). Additional references can be found at the Air Barrier Association of America (ABAA) web site at www.airbarrier.org. (back to top)
2 The impact of air barriers’ vapor permeance on moisture management has been discussed by co-author Spinu in two other articles that were published in The Construction Specifier: April 2007’s “To Be or Not to Be Vapor-Permeable,” and November 2012’s “Designing without Compromise: Balancing Durability and Energy Efficiency in Buildings.” (back to top)
3 The wind loads and schedule considered in these tests have been developed by the ASTM standard committee. While the authors are not part of this committee, it is possible one of the reasons for developing multiple pressure loads is to extrapolate the data at low pressures through linear regression. At low pressure loads, the errors are larger than at high pressures, so it is important to have multiple data points. (back to top)
4 The standards assume the air barrier plane will take the full wind loads (even though this would only be true for pressure-equalized façades). (back to top)
5 The air barrier structural loading is based on the assumption the air barrier plane: (1) takes the full wind loads (even though this only occurs for pressure-equalized façade systems), (2) experiences thousands of cycles of high positive and negative pressure loads during its service life, and (3) experiences two severe storms in the first 15 years of service. The steel studs shown buckling in the picture are at the very high end of the pressure loads. The point is when proper fasteners and spacing are used, air barriers can perform under wind gust conditions. These tests are quite stringent, but air barriers must perform for the life of the building envelope and such conditions could be occasionally experienced. (back to top)

Maria Spinu, PhD, LEED AP, is a building scientist with DuPont Building Knowledge Center, where she has led global building science and sustainability initiatives for the commercial market for the past decade. She is the author of 16 patents and has been a speaker at many regional, national, and international conferences on building science and sustainability topics. Spinu can be contacted via e-mail at maria.spinu-1@dupont.com.

Benjamin Meyer, RA, LEED AP, is a building science architect with DuPont Building Knowledge Center, where he works with customers and industry associations to answer questions on commercial building envelope design. Meyer is on the board of the Air Barrier Association of America (ABAA), a member of the Materials and Resources Technical Advisory Group of LEED, and also a consultant of the ASHRAE 90.1 Envelope Subcommittee. He can be reached benjamin.meyer@dupont.com.

Andrew Miles is a forensics engineer, providing technical support as part of the DuPont Tyvek Specialist network. His responsibilities include mock wall testing and field investigations related to use, performance, and customer concerns. Miles can be e-mailed at andrew.s.miles@dupont.com.

Importance of Qualified SPF Installers

Peter Davis 2013HORIZONS
Peter Davis

Builders, architects, and specifiers have always demanded excellence in themselves, their materials, contractors, and subcontractors. Design professionals find success through various ways, from word of mouth to programs such as EnergyStar or Green Globes, or by seeking professionals certified in their given fields.

The growing sprayed polyurethane foam (SPF) installation industry is a good example of designers reaching out to certified professionals. Popular in both residential and commercial construction, the material seals cracks and gaps in the building envelope, while also providing enhanced air sealing. In the field, installers apply SPF using specialized equipment to mix two liquids. Three main types of SPF exist, each with slightly different characteristics; different products allow for a customized application. In all cases, these liquids chemically react, forming foam that is sprayed on a wall, ceiling, or floor assembly. This spray-applied plastic foam adheres tightly to the framing members of a structure and provides insulating and all-sealing properties. (For more information on the basics of SPF, see Peter Davis’ article, “Making Sense of Sprayed Polyurethane Foam,” in the March 2014 issue of The Construction Specifier.)

Spray polyurethane foam is a spray-applied material widely used to insulate buildings. Photo courtesy Spray Foam Coalition

Sprayed polyurethane foam (SPF) is a spray-applied material widely used to insulate buildings.
Photos courtesy Spray Foam Coalition

As with any material, it is important to consult a qualified contractor when specifying SPF. Qualified contractors and installers are trained—and in some cases, professionally certified—on the proper procedures to use to help keep fellow contractors, installers, and building occupants safe during SPF installation. Training programs offer courses for contractors, while certification programs require participants to demonstrate knowledge through testing of skills and abilities in field exams and/or on-the-job experience, similar to the demarcation of Certified Construction Specifier (CCS) for those who have completed that exam.

Several organizations offer such certification and training programs specifically for SPF installation. For example, the Spray Polyurethane Foam Alliance’s (SPFA’s)Professional Certification Program is for individuals who install and apply insulation and roofing. Certification is earned at the assistant, installer, master installer, and project manager levels. Currently, SPFA’s certification is the only industry-specific certification program developed, designed, and operated in compliance with internationally recognized International Organization for Standardization (ISO) 17024, Conformity Assessment—General Requirements for Bodies Operating Certification of Persons.

SPF’s monolithic nature allows for a seamless, self-flashing roofing application to protect against moisture.

SPF’s monolithic nature allows for a seamless, self-flashing roofing application to protect against moisture.

At the same time, the Air Barrier Association of America (ABAA) provides a three-day onsite training and certification on SPF for air barrier installers at specific locations across the United States. As well, the Center for the Polyurethanes Industry (CPI) offers an online SPF Chemical Health and Safety Training Program for those working with high- and low-pressure, two-component SPF. A certificate of completion is available and can be verified online for the individuals who have successfully completed the course.

Although these programs vary in focus, the shared goal is to provide individuals installing SPF with the information to enhance the professional knowledge, skills, and abilities to install SPF

safely.

Specific topics often covered in training and certification programs can include:
● recommended areas where SPF can be installed;
● which SPF type is best suited for the job at hand;
● how to designate the SPF installation area to address site safety;
● how to confirm the necessary safety precautions and technical specifications are in place;
● what contractors, building owners, and occupants can expect during each stage of installation; and
● how to take advantage of local or federal energy efficiency tax credits or rebates related to SPF.

For example, installers who have been through a certification program will be taught how to obtain and use the proper personal protective equipment (PPE), as well as how long to keep others out of the space during and after installation, since re-entry times can vary depending on the application type and SPF applied.

These types of training programs not only arm contractors with the best available information, but they also enable them to demonstrate their expertise, and help educate specifiers, architects, and builders on the best available practices for SPF installation. They can inform the rest of the project team on SPF applications, the installation process, ventilation needs, and the best safety practices. When contractors demonstrate knowledge in these key areas by successfully completing a professional certification or training program, they can have a profound impact on the rest of the project team.

SPF’s monolithic installation allows it to be used around irregular shapes and penetrations.

SPF’s monolithic installation allows it to be used around irregular shapes and penetrations.

Peter Davis is chairman and CEO of Gaco Western, and chairs the Spray Foam Coalition at the Center for the Polyurethanes Industry of

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the American Chemistry Council. He also serves on the executive committee of the Spray Polyurethane Foam Alliance (SPFA). Davis can be reached via e-mail at pdavis@gaco.com.

Making Sense of Sprayed Polyurethane Foam

All photos courtesy Spray Foam Coalition

All photos courtesy Spray Foam Coalition

 

by Peter Davis

For decades, the U.S. design and construction industry has turned to sprayed polyurethane foam (SPF) to insulate and air seal buildings. SPF can help provide temperature control in various climates, reduce sounds transmitted through the air, and lower construction costs.

When employed as a roofing material, SPF’s monolithic nature allows for a seamless, self-flashing application that can keep out water. It can also improve energy efficiency through its superior insulating and air barrier qualities, helping building owners and general contractors comply with energy codes and meet performance requirements for green building programs and certifications.

As the use of SPF grows, the industry is working to provide answers so architects, engineers, and construction professionals can be confident when specifying SPF insulation or roofing to achieve energy-saving or sound-dampening.

Types of SPF
SPF insulation can be categorized into three main types:

  • low-density, open-cell;
  • medium-density, closed-cell; and
  • high-density, closed-cell.

The molecular structure of the polyurethane cells in the foam produced determines whether SPF is classified as open- or closed-cell. Each type has certain characteristics determining the applications for which it is most appropriate.

Open-cell SPF
Also known as 1/2-pound SPF, which refers to the density of one cubic foot of the product, open-cell SPF is best suited for applications such as ceilings, interior walls, floors, and the underside of roof decks. As a low-density product, this type uses water as the blowing agent. When the foam forms, the water reacts with other chemicals to produce carbon dioxide (CO2), which expands the cells to form semi-rigid porous polymer foam. The CO2 leaves the cells and is replaced with air, hardening the foam.

Spray polyurethane foam (SPF) is a spray-applied material widely used to insulate buildings.

Spray polyurethane foam (SPF) is widely used to insulate buildings.

Closed-cell SPF
Closed-cell SPF, also known as 2-pound foam, is formed by using a blowing agent instead of water. The agent is retained in the closed cells, making the foam rigid and providing exceptional compressive strength. Closed-cell SPF can be further classified into two types: medium- and high-density. The former can be used to insulate:

  • exterior and interior walls;
  • ceilings;
  • floors;
  • slabs and foundation; and
  • the underside of roof decks.

High-density foam is used primarily in flat or low-slope roofing applications, since its density and rigidity lends itself best to this purpose.

Quality installation
One of the most important considerations for architects and builders is selecting a professional contractor to install SPF. Each manufacturer has its own model specification to help architects and specifiers choose the proper product. A contractor should be able to educate architects and builders about the product, its applications, and installation process, including any mechanical ventilation needs during the installation and afterwards.

Qualified contractors can also explain best safety practices, such as the type of protective equipment workers wear and how they keep others out of the space during installation and curing. The latter is especially important, because other trades and building occupants should not be in the area when SPF is being applied and curing. Re-entry time can vary depending on air temperature, humidity level, and the type of SPF applied. Once the product cures, it is considered to be essentially inert, according to the U.S. Environmental Protection Agency (EPA), meaning the chemicals have stopped reacting. (The SPF contractor can advise when it is safe to re-enter the space.)

General contractors and specifiers should consider using an SPF company that employs individuals who have completed the Center for the Polyurethane Industry’s (CPI’s) SPF Chemical Health and Safety Training, and who have been certified by the Spray Polyurethane Foam Alliance’s (SPFA’s) new Professional Certification Program for SPF applicators. The comprehensive certification program, developed in compliance with American National Standards Institute/International Organization for Standardization (ANSI/ISO) 17024, Accreditation Program for Personnel Certification Bodies, focuses on safety, quality installation, and professionalism.

Air, sound, and vapor barrier

SPF’s monolithic installation allows it to be used around irregular shapes and penetrations.

SPF’s monolithic installation allows it to be used around irregular shapes and penetrations.

A reliable air barrier and a continuous seal are essential elements in creating an energy-efficient, comfortable space. Both types of SPF meet the requirements of an air barrier material at a typically installed thickness of 25 mm (1 in.). When installed with other materials in a building assembly, SPF can provide an effective continuous air barrier.

By acting as both insulation and an air barrier, it could even help lower construction costs, because less air sealing materials would be required to meet local and state building energy codes for air leakage mandates.

Since SPF adheres to the substrate, it allows for easy monolithic installation around irregular shapes and penetrations. The material is applied as a liquid and then expands into foam in any nook and cranny in the enclosure to provide a seal. This offers energy performance and occupant comfort.

Open-cell SPF, typically associated with residential applications, is commonly used to fill cavities in interior spaces or to insulate unvented attics. This type is moisture vapor-permeable, and usually requires a properly designed and installed vapor retarder. Generally, open-cell foam has an R-value between R-3 and R-4 per 25 mm (1 in.) of thickness.

Open-cell SPF has also been used on the underside of roof decks in multiple climate zones for years. As with the usage of all building products, the building science of the structure needs to be understood. Potentially, a vapor barrier may be needed with open-cell SPF. Open-cell is vapor permeable, so depending on the structure, design, and climate zone, a determination of whether a vapor barrier needs to be added should be made. If a roof leaks when open-cell SPF is used on the underside of the roof deck, the water will likely gradually move its way through the open-cell SPF. Since it is an open-cellular matrix, the water, in a relatively short period of time if in sufficient quantity, will pass through the foam, and the leak can be identified and then repaired.

Closed-cell is the dominant SPF material for commercial construction, especially when used as an air barrier and thermal insulation system applied on the building’s exterior, or as foundation and slab insulation. This type of SPF has a higher R-value than open-cell—typically between R-6 and R-7 per 25 mm of thickness. Its relatively low moisture permeability means it rarely requires an additional vapor retarder. An exception may apply in areas, such as bathrooms, with high relative humidity (RH).

Regardless of the project type, understanding SPF and its influence on a building’s energy performance is critical. During the design process, architects and general contractors need to take these impacts into account so they can take advantage of SPF’s energy-saving properties. For example, buildings using SPF as the insulation of choice typically require the use of smaller HVAC systems because less air escapes the building, reducing the heating and cooling loads.

SPF insulation seals gaps to reduce air leaks.

SPF insulation seals gaps to reduce air leaks.

SPF benefits
While SPF is most often associated with energy-saving properties, it has numerous other benefits, including soundproofing. In commercial and residential buildings, open-cell foam is typically used in interior partitions for sound control. Since SPF seals the cracks and crevices in a building, and adds another layer between the interior and exterior, it helps dampen noises that travel through the air, such as the sound of an airplane overhead or a phone conversation in the adjoining office.

Given SPF’s ability to air seal, it is necessary to design proper air distribution systems to control moisture and air flow within the finished building. While a continuous seal is desired, interior spaces require a certain amount of outside ventilation to maintain air quality. Similarly, moisture created by cooking and bathing must be able to dissipate safely within the building.

Structural integrity
Ultimately, all construction projects are judged on their integrity—how long they can withstand the tests of the elements and time. SPF, especially closed-cell foam, enhances a building’s strength and stability because of its rigid structure.

Many of the properties making SPF effective as a stabilizer also make it attractive for flat roofing applications. SPF roofing, a high-density closed-cell foam, can form a continuous insulation (ci) barrier on the top of a roof deck. Since SPF roofing has no seams or joints and is rigid, it forms an impermeable surface. Since it is fully adhered to the substrate, the rigid foam provides exceptional uplift resistance during severe storms producing high winds.

About 10 months after Hurricane Katrina, the National Institute of Standards and Technology (NIST) issued, “Performance of Physical Structures in Hurricane Katrina and Hurricane Rita: A Reconnaissance Report”1 on damage to buildings in the Pascagoula, Mississippi area. It found all but one of the buildings with SPF roofs made it through the storm “extremely well without blow-off of the SPF or damage to flashings.” For the building that was the lone exception—just one percent of its roof area had failed.

An SPF roof properly maintained with regular recoats of the exterior membrane can last for decades. According to SPFA, some SPF roofs have lasted for more than 30 years. Closed-cell SPF also enhances a structure’s resistance to water damage. By acting as a barrier to water and condensation in the building envelope, SPF can help a building resist the growth of mold and mildew. Its ability to adhere to and around surfaces ensures every nook and cranny is filled, so there are no spots for these to grow. Its water-proofing abilities extend to increased floodwater protection as well.

Closed-cell SPF is a material that meets Federal Emergency Management Agency (FEMA) requirements for a Class 5 flood-resistant material—the highest class of materials that can resist damage from floods, according to a FEMA technical bulletin, “Flood Damage-resistant Materials Requirements for Buildings Located in Special Flood Hazard Areas in accordance with the National Flood Insurance Program.” This class of material can submerged for 72 hours, and can easily be dried and cleaned following a flood.

SPF’s monolithic nature allows for a seamless, self-flashing roofing application to protect against moisture.

SPF’s monolithic nature allows for a seamless, self-flashing roofing application to protect against moisture.

Green building benefits
As green building practice and techniques become the norm, many building owners, designers, and general contractors want to reduce the environmental impact of buildings. Due to its superior insulating qualities, SPF allows the building community to achieve a balance between energy efficiency, building durability, and comfort. It can also help them meet the requirements of programs such as EnergyStar and the Leadership in Energy and Environmental Design (LEED) rating program. Additionally, a study by SPFA, “Life Cycle Assessment of Spray Polyurethane Foam Insulation for Residential & Commercial Building Applications,” found energy and environmental benefits of using SPF for retrofits of non-residential roofs and residential applications outweigh the amount of energy and environmental impacts associated across the product’s lifecycle.2

Conclusion
With several types of SPF available and numerous application possibilities, it is worthwhile for architects, specifiers, and builders to gain a deeper understanding of this product. SPF allows for more creative design, filling in cavities and covering surfaces that could otherwise pose challenges. It helps reduce air infiltration, eliminating intrusions from dust and pollen and making buildings more comfortable. As a roofing material and exterior insulator, SPF can strengthen a structure by increasing its water resistance and durability.

Notes
1 To read this report, visit www.nist.gov/customcf/get_pdf.cfm?pub_id=908281. (back to top)
2 The “Life Cycle Assessment of Spray Polyurethane Foam Insulation for Residential & Commercial Building Applications” report can be viewed at www.sprayfoam.org/files/docs/SPFA%20LCA%20Long%20Summary%20New.pdf. (back to top)

Peter Davis is chairman and CEO of Gaco Western, chairman of the Spray Foam Coalition at the Center for the Polyurethanes Industry, and serves on the executive committee of the Spray Polyurethane Foam Alliance (SPFA). He can be reached via e-mail at pdavis@gaco.com.